I. Short answer type questions:
1. Name the acid present in lemon juice.
Ans. Citric acid.
2. Name the acid present in ant sting.
2. Name the acid present in ant sting.
Ans. Formic acid.
3. Name the acid presents in our stomach.
3. Name the acid presents in our stomach.
Ans. Hydrochloric acid.
4. What is common to both acid and base?
Ans. Both acids, as well as bases, produce salts when reacts with metal oxides.
5. Write the name of a compound known as Lewis acid & one as Lewis base.
Ans. Lewis acid that gives H+ ions electron-pair acceptor and Lewis base that gives -OH ions when reacts with water respectively.
Ans. Lewis acid that gives H+ ions electron-pair acceptor and Lewis base that gives -OH ions when reacts with water respectively.
6. How zinc metal reacts with conc. caustic soda? Write the chemical equation.
Ans. When granulated zinc metal reacts with the solution of sodium hydroxide (caustic soda-NaOH)it produces sodium zincate.
2NaOH + Zn→ Na2 ZnO2 + H 2
(Sodium zincate )
Ans. When granulated zinc metal reacts with the solution of sodium hydroxide (caustic soda-NaOH)it produces sodium zincate.
2NaOH + Zn→ Na2 ZnO2 + H 2
(Sodium zincate )
7. What is the alternate name of the term negative log [H+]?
Ans. pH is the negative logarithm of the hydrogen ion concentration.
pH = - log[H+]
Ans. pH is the negative logarithm of the hydrogen ion concentration.
pH = - log[H+]
8. Name the plant which on rubbing gives relief to the skin affected by stinging nettles(methanoic acid).
Ans. The leaf of the dock plant which on rubbing gives relief to the skin affected by stinging nettles (methanoic acid-CH3COOH), which often grows beside the nettle in the wild.
Ans. The leaf of the dock plant which on rubbing gives relief to the skin affected by stinging nettles (methanoic acid-CH3COOH), which often grows beside the nettle in the wild.
9. If H+ concentration of a solution is 1 x 10-2 Mol/L, what will be its pH value?
Ans. We have pH = - log[1 x 10-2]
= -(-2log10)
= 2. [ log10=1]
pH value = 2
Ans. We have pH = - log[1 x 10-2]
= -(-2log10)
= 2. [ log10=1]
pH value = 2
10. Give one example of each of the basic oxide and acidic oxide.
Ans. CaO is basic oxide and CO2 is an acidic oxide.
Ans. CaO is basic oxide and CO2 is an acidic oxide.
11. Give an example of a natural indicator and synthetic indicator.
Ans. A natural indicator is a litmus solution and a synthetic indicator is methyl orange.
Ans. A natural indicator is a litmus solution and a synthetic indicator is methyl orange.
12. Write the name of a highly water-soluble base and strong acid with the molecular formula.
Ans. A highly water-soluble base is sodium hydroxide - NaOH
and a strong acid is H2SO4.
13. Name the gases evolved at anode and cathode by the electrolysis of brine?
Ans. By the electrolysis of brine (NaCl), chlorine gas is evolved at the anode and hydrogen gas is evolved at the cathode.
Ans. By the electrolysis of brine (NaCl), chlorine gas is evolved at the anode and hydrogen gas is evolved at the cathode.
14. Amongst dry HCl and HCl solution, which can show the acidic property?
Ans. HCl solution forms hydronium ions which are responsible for an acidic character in the presence of water so HCl solution can show the acidic property.
Ans. HCl solution forms hydronium ions which are responsible for an acidic character in the presence of water so HCl solution can show the acidic property.
15. A chemical substance is used to set the fractured bones in the right position. Give the chemical name and formula of this substance.
Ans. Plaster of Paris.
Ans. Plaster of Paris.
Semi hydrated calcium sulphate ( CaSO 4 . 1/2 H 2O ).
16. What is the salt of sulphuric acid, nitric acid, and hydrochloric acid?
Ans. Salt of sulphuric acid is sulphate salt. Ex- CaSO4
Salt of nitric acid is nitrate salt. Ex - Na2NO3
Salt of hydrochloric acid is chloride salt. Ex - NaCl
Ans. Salt of sulphuric acid is sulphate salt. Ex- CaSO4
Salt of nitric acid is nitrate salt. Ex - Na2NO3
Salt of hydrochloric acid is chloride salt. Ex - NaCl
17. Write three strong acids and three weak acids.
Ans. Three strong acids are Sulphuric acid (H2SO4), Nitric acids (HNO3) and Hydrochloric acids (HCl).
Three weak acids are Formic acid(HCOOH), Acetic acid (CH3COOH)) and carbonic acid (H2CO3).
Ans. Three strong acids are Sulphuric acid (H2SO4), Nitric acids (HNO3) and Hydrochloric acids (HCl).
Three weak acids are Formic acid(HCOOH), Acetic acid (CH3COOH)) and carbonic acid (H2CO3).
18. What is the ideal pH of the soil for the healthy growth of a plant?
Ans. The optimal pH range of the soil for the healthy growth of a plant is between 5.5 and 7.0
Ans. The optimal pH range of the soil for the healthy growth of a plant is between 5.5 and 7.0
19. What is the difference between baking powder and washing soda?
Ans. Sodium bicarbonate NaHCO3 is a baking powder used for baking cakes, bread, etc. Hydrated sodium carbonate Na2CO3.10H2O is a washing soda that contains used for washing clothes.
Ans. Sodium bicarbonate NaHCO3 is a baking powder used for baking cakes, bread, etc. Hydrated sodium carbonate Na2CO3.10H2O is a washing soda that contains used for washing clothes.
20. Which gas is usually liberated when an acid reacts with a metal?
Ans. Hydrogen gas is liberated when an acid reacts with metal.
Ans. Hydrogen gas is liberated when an acid reacts with metal.
21. Which is a stronger acid with pH = 5 or with pH = 2 ?
Ans. With pH = 2 is stronger acid.
Ans. With pH = 2 is stronger acid.
22. What is the effect of dilution on the H+ ion concentration of an acid?
Ans. Mixing an acid with water results in a decrease in the concentration of ions H+ per unit volume.
Ans. Mixing an acid with water results in a decrease in the concentration of ions H+ per unit volume.
23. A compound that is formed due to the recrystallization of sodium carbonate. Identify the compound and write its chemical formula.
Ans. Washing soda is formed due to the recrystallization of sodium carbonate. Na2CO3 + 10H2O → Na2CO3.10H2O
(Sodium carbonate)
Ans. Washing soda is formed due to the recrystallization of sodium carbonate. Na2CO3 + 10H2O → Na2CO3.10H2O
(Sodium carbonate)
24. What do you understand by the term water of crystallization?
Ans. The water of crystallization is the fixed number of water molecules chemically attached to each formula unit of salt in its crystalline form.
Ans. The water of crystallization is the fixed number of water molecules chemically attached to each formula unit of salt in its crystalline form.
25. Name a salt which does not contain water of crystallization.
Ans. Bleaching powder- CaOCl2 which does not contain water of crystallization.
Ans. Bleaching powder- CaOCl2 which does not contain water of crystallization.
26. ith a gas such as nitrogen.
Ans. Nitrogen gas is less reactive and it protects chips from rancid.
Ans. Nitrogen gas is less reactive and it protects chips from rancid.
27. Fresh milk has a pH of 6. When it changes into curd will its pH value increase or decrease? Why?
Ans. Fresh milk contains lactose and has a pH value 6. Due to the fermentation of lactose by lactic bacteria lactose changes into lactic acids and milk changes into curd hence its pH value decrease.
Ans. Fresh milk contains lactose and has a pH value 6. Due to the fermentation of lactose by lactic bacteria lactose changes into lactic acids and milk changes into curd hence its pH value decrease.
28. What would be the colour of litmus in a solution of sodium carbonate?
Ans. Sodium carbonate is basic in nature and the red colour of litmus changes into blue and blue litmus does not change.
Ans. Sodium carbonate is basic in nature and the red colour of litmus changes into blue and blue litmus does not change.
29. Why does tooth decay start when the pH value of the mouth is lower than 5.5?
Ans. Tooth enamel made up of calcium phosphate is the hardest substance in the body is corroded when the pH in the mouth is below 5.5 and tooth decay starts.
Ans. Tooth enamel made up of calcium phosphate is the hardest substance in the body is corroded when the pH in the mouth is below 5.5 and tooth decay starts.
30. How does the use of toothpaste help in preventing tooth decay caused due to eating chocolate and sweets?
Ans. Toothpaste is generally basic and neutralizes excess acid formed due to eating chocolate and sweets and prevent tooth decay.
Ans. Toothpaste is generally basic and neutralizes excess acid formed due to eating chocolate and sweets and prevent tooth decay.
31. What effect does an increase in the concentration of H+ in a solution have on the pH of the solution?
Ans. Increase in H+ ion concentration, its pH starts decreasing and it makes the solution more acidic than before.
Ans. Increase in H+ ion concentration, its pH starts decreasing and it makes the solution more acidic than before.
32. Which one of these has a higher concentration of H+ ions? 1M HCl or 1M CH3COOH.
Ans. 1M HCl has a higher H+ ions because of it completely ionized and formes more hydrogen ion than CH3COOH.
Ans. 1M HCl has a higher H+ ions because of it completely ionized and formes more hydrogen ion than CH3COOH.
33. During the summer season, a milkman usually adds a very small amount of baking soda to fresh milk. Give one reason.
Ans. During the summer season, a milkman usually adds a very small amount of baking soda which is alkaline, it neutralizes excess acid in the milk and keeps the milk from becoming sour for a long time.
Ans. During the summer season, a milkman usually adds a very small amount of baking soda which is alkaline, it neutralizes excess acid in the milk and keeps the milk from becoming sour for a long time.
34. How does the change in pH value of milk when it changes to curd. Explain.
Ans. pH value of milk is decreased when it changes into curd because the curd contains lactic acids.
Ans. pH value of milk is decreased when it changes into curd because the curd contains lactic acids.
35. Write the reactions which take place when baking soda is heated during cooking.
Ans. The following reaction takes place when it is heated during cooking –
2NaHCO3 + Heat→ Na2CO3 +H2O+CO2
(Sodium hydrogen carbonate) (Sodium carbonate)
Sodium hydrogen carbonate has got various uses in the household.
Ans. The following reaction takes place when it is heated during cooking –
2NaHCO3 + Heat→ Na2CO3 +H2O+CO2
(Sodium hydrogen carbonate) (Sodium carbonate)
Sodium hydrogen carbonate has got various uses in the household.
36. Write an equation to show the reaction between the plaster of Paris and water.
Ans. When the white powder Plaster of Paris reacts with water, it changes to gypsum and forms a hard solid mass.
CaSO4 .1/2 H2O + 1 1/2 H 2O → CaSO4 .2H 2O
(Plaster of Paris) (Gypsum)
37. Name a substance that on treatment with chlorine yields bleaching powder.
Ans. Dry slaked lime [Ca(OH)2] is a substance that on treatment with chlorine to produce bleaching powder-CaOCl2.
Ans. When the white powder Plaster of Paris reacts with water, it changes to gypsum and forms a hard solid mass.
CaSO4 .1/2 H2O + 1 1/2 H 2O → CaSO4 .2H 2O
(Plaster of Paris) (Gypsum)
37. Name a substance that on treatment with chlorine yields bleaching powder.
Ans. Dry slaked lime [Ca(OH)2] is a substance that on treatment with chlorine to produce bleaching powder-CaOCl2.
38. Name the sodium compound which is used for softening hard water.
Ans. Na2CO3.10H2O (washing soda) is used for softening hard water.
2. A piece of zinc metal is dropped in a dilute solution of hydrochloric acid.
(a) Which gas is liberated when a metal reacts with an acid?
(b) How will you test the presence of this gas?
(c) Is it lighter or heavier than air?
(d) How will you collect the above gas?
25. Explain and write the chemical formula of baking soda. How is baking soda prepared?
Ans. The chemical name of the baking soda is sodium hydrogen carbonate (NaHCO3). It is produced by the using of sodium chloride as one of the raw materials.
NaCl + H2O + CO2 + NH3 →NH4Cl + NaHCO3
(Sodium chloride) (Ammonium hydrogen carbonate)
III. Long answer type questions:
3. Comment on the following :
(i) An acid reacts with substance X produces a gas that burns with a pop sound. What is the nature of X?
(ii) An acid when reacting with Z produces CO2 gas. What can be Z?
(iii) CaO and SO2 are two oxides. Name the oxide which will base?
(iv) A sodium compound is used for removing the permanent hardness of the water. Name the compound.
(v) A substance on treatment with chlorine gas yields bleaching powder. Name the substance.
6. A metal carbonate X on reacting with acid gives a gas which when passed through a solution Y gives the carbonate back. On the other hand, a gas G that is obtained at the anode during electrolysis of brine is passed on dry Y, it gives a compound Z, used for disinfecting drinking water. Identify X, Y, G, and Z .
7. For the baking cake, baking powder is taken. If at home you have backing soda instead of baking powder:
(i) How will it affect the test of the cake?
(ii) How can baking soda be converted into baking powder?
(iii) What is the role of tartaric acid added to baking soda?
Ans. (I) Baking powder is a base and bitter in the test so the test of cake becomes slightly bitter.
(ii) Baking soda can be converted into baking powder by adding mild edible acid such as tartaric acid. Tartaric acid is present in tamarind which reduces the bitter test of the baking soda.
(iii) Tartaric acid reduces the bitterness of cake baking soda is a base and bitter in the test so tartaric acid reacts with baking soda and neutralise the bitter test.
8. What is bleaching powder? How is it prepared? list two uses of bleaching powder.
Or
[Do your self: (a) Write the common name of CaOCl2 How is it prepared. Write the chemical equation of the reaction involved in the process. Give any two uses of it.
(b) Write the chemical name of washing soda. How is it prepared? Give the relevant chemical equation.]
Ans. Bleaching powder is a salt, calcium oxychloride ( CaOCl2,).
Preparation of CaOCl2: chlorine is produced by the electrolysis of aqueous sodium chloride (brine). This chlorine gas is used or the manufacture of bleaching powder. Bleaching powder is produced by the action of chlorine on dry slaked lime Ca(OH)2.
Ca(OH)2 + Cl2 → CaOCl2 + H2O
(i) It is used for disinfecting drinking water to make it free of germs.
(ii) It is used for bleaching cotton, linen, wood pulp, washed clothes in the laundry and
(ii) It is used as an oxidising agent in many chemical industries.
9. (a) What would be the colour of the solution when copper oxide and dilute hydrochloric acid are mixed?
(b) Write a chemical equation that represents that the effect of a base is nullified by an acid and vice versa.
Ans. (a) The colour of the solution becomes blue-green when copper oxide and dilute hydrochloric acid are mixed.
When copper oxide reacts with hydrochloric acid to produces copper chloride and water.
CuO + HCl → CuCl2 + H2O
(blue green)
(b) When hydrochloric acid reacts with base sodium hydroxide it formes a neutral salt and water. This reaction is known as neutralisation reaction. In this reaction both acid and base netralises each other.
NaOH + HCl → NaCl + H2O
10. A dry pellet of a common base B, when kept in open absorbs moisture and turns sticky. The compound is also a by-product of Chlor- alkali process Identify B. What type of reactions occurs when B is treated with an acidic oxide.
Ans. A dry pellet of a common base B is sodium hydroxide NaOH, when kept in open absorbs moisture and turns sticky. NaOH is a by-product of chlor- alkali process.
Chlor-alkali process:
NaCl + H2O → NaOH + Cl2 + H2
When sodium hydroxide which is a base reacts with acidic oxide solution like CO2 which is acidic in nature, produces salt and water and this type of reaction is called neutralisation reaction.
NaOH + CO2 → NaCO3+ H2O
11. Write the chemical formula of the following salt and obtained from which acid or base:
(i) Ammonium chloride. ( ii) Copper Sulphate
(iii) Sodium chloride (iv) Magnesium Nitrate
(v) Potassium Sulphate. (vi) Calcium nitrate.
Ans. (i) Ammonium Chloride - NH4Cl
Acid - HCl, Base - NH4OH
(ii) Copper Sulphate - CuSO4.
Acid - H2SO4, Base - Cu(OH)2.
(iii) Sodium Chloride - NaCl
Acid - HCl, Base - NaOH
(iv) Magnesium Nitrate - Mg(NO3)2
Acid - HNO3, Base - Mg(OH)2
(v) Potassium Sulphate - K2SO4
Acid - H2SO4, Base - KOH
(vi) Calcium Nitrate- Ca(NO3)2
Acid - HNO3, Base Ca(OH)2.
12. While constructing a house a builder select marble flooring and marble tabletop for the kitchen where vinegar, juices of lemon, and tamarind, etc. are more often used for cooking. Will you agree to this selection and why?
Ans. Vinegar, juices of lemon, and tamarind, etc. are contain acetic acids, citric acid and tarteric acid. These acids can react with marble which is calcium carbonate. So when accidentally these acids fall on the floor of the marble, marble rapidly reacts with these acids and causes a chemical reaction and marble can be damaged.
So I will not agree with this selection.
13. A white powder A is the mild non-corrosive base and is used in the preparation of cakes. When the powder A is heated it gives another powder B.The powder B is recrystallized to get a substance C that has detergent properties. Identify A, B, and C and also write balanced chemical equations for the conversions of A to B and then B to C.
Ans. NaHCO3 is the mild non-corrosive base and is used in the preparation of cakes. When NaHCO3 is heated it gives powder of Na2CO3 and when this powder is recrystallised to get Na2CO3.10H2O that has detergent properties.
Therefore A is sodium bicarbonate NaHCO3, B is sodium carbonate Na2CO3, and C is hydrated sodium carbonate Na2CO3.10H2O.
2NaHCO3 + Heat → Na2CO3 + H2O + CO3
(Sodium (Sodium carbonate)
hydrogen carbonate)
Na2CO3 + 10H2 O → Na2CO3.10H2O
( Washing soda)
14. A substance is used as an antacid reacts with hydrochloric acid to produce a gas Y which is used in extinguishing the fire.
(a) Name the substance X and gas Y.
(b) Write a balanced chemical equation of the reaction between X and hydrochloric acid.
Ans. Sodium bicarbonate NaHCO3 is an antacid reacts with hydrochloric acid HCl to produce a gas CO2 which is used in extinguishing the fire.
(a) X is NaHCO3 and Y is CO2 gas.
(b) A balanced chemical equation of the reaction between NaHCO3 and hydrochloric acid :
When sodium bicarbonate reacts with hydrochloric acid to produce sodium chloride water and carbondioxide gas.
2NaHCO3 + HCl → NaCl + H2O + CO3
15.(a) Write the name given to bases that are highly soluble in water. Give an example.
(b) How is tooth decay related to pH? How can it be prevented?
(c) Why does bee-sting cause pain and irritation? Rubbing of baking soda on the sting area gives relief. How?
Ans. (a) Sodium hydroxide, potassium hydroxide calcium hydroxide. etc are highly soluble in water.
(b) Tooth decay starts when the pH of the mouth is lower than 5.5. Tooth enamel does not dissolve in water but is corroded when the pH in the mouth is below 5.5. Bacteria present in the mouth produce acids by the degradation of sugar and food particles remaining in the mouth after eating.
The best way to prevent this is to clean the mouth after eating food. Using toothpaste, which is generally basic, for cleaning the teeth can neutralize the excess acid and prevent tooth decay.
(c) Bee-sting leaves an acid which causes pain and irritation. The use of a mild base like baking soda on the stung area gives relief.
16. I. Differentiate between strong and weak acids. Identify the strong and weak acids from the following list of acids: hydrochloric acid, acetic acid, formic acid, nitric acid.
II. What is meant by the term hydrated salt? Give two examples of hydrated salt which are white and state their chemical formula.
Ans. I. The strength of acids depends on the number of H+ ions produced.
Strong acids are acids that are completely dissociated and give rise to more H+ ions and weak acids are acids that do not completely dissociate or partially dissociate and gives to rise less H + ions.
Nitric acid and hydrochloric acid are strong acids.
Formic acid is a weak acid.
II. Hydrated salt is the salt that contains water of crystallisation which is the fixed number of water molecules in one formula unit of salt.
Example two hydrated salts are:
i. Plaster of Paris that is hemihydrate calcium sulphate which contains half molecules of water- CaSO4 .1/2 H2O
ii. Washing soda that is hydrated sodium carbonate which contains ten molecules of water - Na2CO3.10H2O.
17. A compound which is prepared from gypsum has the property of hardening when mixed with the right quantity of water.
(a) Identify the compound and write its chemical formula.
(b) Write the chemical equation for its preparation.
(c) List any two uses of the above compound.
Ans. (a) The plaster of Paris is prepared from gypsum and it becomes hard when mixed with the proper quantity of water.
(b) At 373 K, on heating gypsum, it loses water molecules and becomes hemihydrate calcium sulphate (CaSO4 .1/2 H2O) which is known as Plaster of Paris.
2CaSO4.2H2O + Heat → 2CaSO4.1/2H2O + 3H2O
(c) i. It is used by doctors as plaster for supporting fractured bones in the right position.
ii. It is used as decorative in buildings.
18. A student dropped a few pieces of marble in dilute hydrochloric acid contained in a test tube the evolved gas was then passed through lime water, what change would be observed in lime water? What will happen if excess of gas is passed through lime water?
Ans. When a student drops a few pieces of marble in dilute hydrochloric acid contained in a test tube the carbon dioxide gas evolved. When CO2 gas passed through lime water, lime water turns milky due formation of white precipitate CaCO3.
On passing the carbon dioxide gas evolved through lime water:
Ca(OH)2 (aq)+ CO2 (g)⟶ CaCO3(s) + H2O(l)
(Lime water) (White precipitate)
If an excess of gas is passed through the lime water then colourless soluble calcium bicarbonate is formed.
CaCO3(s) + H2O(l) + CO2 (g) → C(HCO3)2(aq)
19. I. You are given two solutions A and B. The pH of solution A is 6 and pH of solution B is 8
(a) Identify the acidic and basic solutions.
(b) Which solution has more H+ ion concentration? Give reasons for your answer.
II Why is HCl a stronger acid than acetic acid? Explain.
Ans. I. (a) pH value of A is less than 7 so it is an acidic solution and pH value of B is more than 7 so it is a basic solution.
(b) Solution A has more H+ ion concentration.
Reason: When pH value is 6 means the power of hydrogen is 6.
And the concentration of H+ ion is equal to 10^-6 Mol/L
For B pH is 8 and the concentration of H+ ion is equal to 10^-8 Mol/L
10^-8 < 10^-6
Therefore B has less H+ ion concentration.
II. Hydrochloric acids give more H+ ions by completely dissociation so they are said to be strong acids, and acetic acids give less H+ ions by partial dissociation so they are said to be weak acids.
[Note: To find the concentration of H+ : If pH = 7 = 7 x 1 = 7log10=log10^7 = log 1/10^-7 [log10 = 1]....1
And pH= log10 1/[H+]....2
Given pH=7
From eq. 1 & 2 we get
-log[H+] = log10^-7
H+ = 10^-7]
20. When a concentrated aqueous solution of substance X is electrolyzed, then NaOH, Cl2 and H2 are produced.
(a) Name the substance X
(b) What is the special name of this process and why is it so-called?
(c) Which gas is liberated at the anode? List one uses of this process.
Ans. (a) X is sodium chloride (NaCl) called brine.
When a concentrated aqueous solution of NaCl is electrolyzed, then NaOH, Cl2 and H2 are produced.
2NaCl + 2H2O → 2NaOH + Cl2 + H2
(b) This process is known as Chlor-alkali process because of the products formed– chlor for chlorine and alkali for sodium hydroxide.
(c) Chlorine Cl2 is liberated at the anode. This process is used for the manufacture of bleaching powder.
21. What is the chloralkali process? Why is it so-called? Write the equation for the reaction.
Name the three products of the chlor-alkali process. Write one commercially or industrially important material is that can be prepared from each of these products.
Ans. When electricity is passed through an aqueous solution of sodium chloride (called brine), it decomposes to form sodium hydroxide. This process is called the chlor-alkali process.
This process is called the chlor-alkali process because of the products formed– chlor for chlorine and alkali for sodium hydroxide.
22. "Sodium hydrogen carbonate is a basic salt "Justify the statement. How is it converted into washing soda? Explain.
Ans. : Basic salt is a salt produced by the reaction between a strong acid and a weak base. Sodium hydrogen carbonate produced by the reaction between a strong base (NaOH) and a weak acid (H2CO3), so it is a basic salt.
NaOH + H2CO3 → NaHCO3 + H2O
Sodium hydrogen carbonate is heated strongly to produce sodium carbonate.
NaHCO3 + Heat → Na2CO3 + H2O + CO2
Na2CO3 + 10H2O → Na2CO3.10H2O.
(Sodium carbonate)
23. There are three test tubes A, B, C. Test tube A has an acidic solution, test tube B has a basic solution and test tube C has distilled water. Identify the contents of each test tube with the help of litmus paper.
Ans. Test tube A has an acidic solution. Therefore the colour of blue litmus paper changes to red and the colour of red litmus paper does not bring out any change in the solution.
Test tube B has a basic solution. Therefore the colour of red litmus paper changes to blue in the solution and the colour of blue litmus paper does not bring out any change in the solution.
Test tube C has distilled water. Hence the solution is neutral so it does not bring out any change in the colour of litmus paper.
24. A liquid has a pH of less than 7 which is represented as an acidic solution.
(a) State the nature of the solution if its pH increases from 7 to 14.
(b) Mention the ion concentration increases with an increase in pH value.
(c) Suggest a method that is generally used for measuring PH value.
Ans. (a) As the pH value increases from 7 to 14, that is an increase in the strength of alkali.
(b) As the pH value increases, it represents an increase in (OH–) ion concentration and decreases in H+ ion concentration in the solution.
(c) The method that is generally used for measuring PH value is:
pH= - log10 [H+]
25. A few crystals of copper Sulphate is heated in a dry boiling tube:
(a) What is the colour before and after heating?
(b) What is the reason for the colour change?
(c) Can its original colour be restored? How?
Ans. (a) The colour of copper Sulphate before heating is blue due to the presence of crystal of water molecules.
(b) When we heat the crystals of hydrated copper sulphate, its water turns into water vapour and hydrated copper sulphate converted into anhydrous copper sulphate. so the colour of the crystals turns blue to white-grey in colour .
CuSO4.5H2O + Heat → CuSO4 + 5.H2O
(c) yes, its original colour can be restored by cooling and adding water.
Anhydrous copper sulphate converted into hydrated copper sulphate which is blue in colour.
CuSO4 + 5.H2O → CuSO4.5H2O
26. I.Giving reasons for each state which of the following will conduct electricity and which will not :
(a) A solution of glucose
(b) Dilute hydrochloric acid?
II.(a) If acetic acid and hydrochloric acid of the same concentration are taken, which of the two is stronger acid and why?
(b) How is the strength of an acid affected when some water is added to it?
Ans. (a) A solution of glucose does not conduct electricity because the electric current is carried through the solution by ions and glucose does not contain ions in solution.
(b) Dilute hydrochloric acid conduct electricity because it contains cation H+ which is responsible for conduct electricity.
II. (a) Hydrochloric acid is stronger than acetic acid of the same concentration because it completely dissociates into ions but acetic acid does not.
(b) When some water is added to an acid, results in a decrease in the concentration of ions (H3O+) per unit volume and the acid is said to be diluted. Hence the strength of an acid is decreased.
27. I. While eating food, you happen to spill some curry on your white shirt. You immediately scrub with soap. What happens to its yellow colour? What happens to this stain when the shirt is washed with plenty of water?
II. (a) Write the chemical formula of plaster of Paris and Gypsum.
(b) How can plaster of Paris be converted into gypsum?
(c) List anyone uses of plaster of Paris.
Ans. I. Curry contains turmeric which is yellow in colour and is a natural indicator for the base. When the shirt is scrubbed with soap which is a base, react with the turmeric present in the curry to form a reddish colour substance in the shirt, so the colour of yellow on the shirt becomes red.
When the shirt is washed with plenty of water its reddish colour substance removed and the colour of the stain becomes yellow.
II. (a) The chemical formula of plaster is Hemi hydrated calcium sulphate. CaSO4.1/2H2O
(b) When plaster of Paris mixed with the proper amount of water is converted into a hard mass of gypsum CaSO4.2H2O.
CaSO4.1/2H2O + CaSO4.2H2O.
(c) It is used by doctors as plaster for supporting fractured bones in the right position.
28. Rahul has been stung by the honey bee and is in great pain.
(a) What could be the reason for this burning pain? State the type of chemical compound that can be applied to the affected area to give relief to Rahul.
(b) Write the name and formula of each of the following:
(i) an acidic salt (ii) a basic salt (iii) a neutral salt.
Ans. (a) Honey bee-sting leaves an acid which causes a great pain and irritation. The use of a base like baking soda on the stung area gives relief to Rahul.
(b) (i) An acidic salt is formed by the reaction between a strong acid and a weak base. Ex -Ammonium chloride NH4Cl.
NH4Cl is formed by the reaction of weak base NH4OH and strong acid HCl.
NH4OH + HCl → NH4Cl + H2O
(ii) A basic salt is formed by the reaction between a strong base and a weak acid. Ex -Sodium acetate - CH3COONa.
CH3COONa is formed by the reaction of strong base sodium hydroxide NaOH and weak acid acetic acid CH3COOH.
CH3COOH + NaOH → CH3COONa + H2O
(iii) A neutral salt is formed by the reaction between a strong acid and a strong base. Ex -Ammonium chloride NaCl.
NaCl is formed by the reaction of strong base NaOH and strong acid HCl.
NaOH + HCl → NaCl + H2O
29. I. A local musician was showing magic in a village street. He took eggshells and poured a solution over it. As a result, if an effervescence were formed. When he took a burning matchstick over it, went off:
(a) Identify the solution poured and a substance present in eggs.
(b) What is the reason behind the effervescence?
(c) Write its balanced chemical equation.
(d) Give the common name of the substance present in eggshell.
Ans. I. (a) The solution poured is acid and a substance present in eggs is calcium carbonate CaCO3.
(b) When an acid reacts with calcium carbonate present in the eggshell to produce carbon dioxide gas which is the reason behind the effervescence.
(c) Chemical reaction is :CaCO3 + H2SO4 → CaSO4 + CO2 + H2O.
(d) Calcium carbonate is resent in eggshell.
30. (a) Acids as well as bases ionized in water. Name the ions produced by each in water.
(b) If we have hydrochloric acid and acetic acid of equal concentration, which will be a strong acid and why?
(c) How will the concentration of hydrogen ion get effected if acid is diluted?
Ans. (a) Acids as well as bases ionized in water. Acid produces hydronium ions in water.
HCl → H+ + Cl-
H+ + H2O → H3O+
(hydronium ions)
(b) Hydrochloric acid is stronger than acetic acid of the same concentration because it completely dissociates into ions but acetic acid does not.
(c) Dilution of acid by mixing water results in a decrease in the concentration of ions (H3O+) per unit volume.
31. (a) Identify the acid and base whose combination forms the common salt that you use in your food. Write the formula and chemical name of this salt. Name the source from where it is obtained.
(b)What is rock salt? Mention its colour and the reason due to which it has this colour.
(c) What happens when electricity is passed through brine? Write the chemical formula for it.
Ans. (a) The acid HCl and the base NaOH whose combination forms the common salt NaCl that we use in your food. The main source of common salt is seawater.
(b) Seawater contains many salts dissolved in it. Sodium chloride is separated from these salts. Deposits of solid salt are also found in several parts of the world. These large crystals are often brown due to impurities. This is called rock salt.
(c) When electricity is passed through an aqueous solution of sodium chloride called brine, it decomposes to form sodium hydroxide.
2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2(g) + H2(g)
Chlorine gas is given off at the anode, and hydrogen gas at the cathode. A sodium hydroxide solution is formed near the cathode.
32. (a) Write the chemical name and chemical formula of washing soda.
(b) How it is obtained from sodium chloride? Give equations of the reaction?
(c) Why is it called a basic salt? Give its anyone uses?
Ans. (a) The chemical name of washing soda is hydrated sodium carbonate and the formula is Na.CO3.10H2O.
(b) NaHCO3 is produced by using sodium chloride as one of the raw materials.
NaCl + H2O + CO2 + NH3 → NH4Cl + NaHCO3
(Sodium chloride) (Ammonium hydrogen carbonate)
When sodium hydrogen carbonate is heated to produce sodium carbonate.
2NaHCO3 + Heat → Na2CO3 + H2O + CO2.
The recrystallization of this sodium carbonate gives washing soda.
Na2CO3 + 10H2O → Na2CO3.10H2O.
33. (a) Name the gas which is liberated when an acid reacts with metal. How will you test the presence of this gas?
(b) Write the chemical equation for the reaction of Zinc metal with.
(i) Hydrochloric acid and (ii) With Sodium hydroxide. Write the chemical name of salt obtained in each case.
(b)Identify the acid and base for Ammonium chloride salt. What would be the nature of the salt? Mention the pH range of the salt.
Ans. (a) Hydrogen gas is liberated when an acid reacts with the metal.
Burning of hydrogen gas with pop sound is the test of hydrogen gas.
(b) (i) Zn metal reacts with HCl to produce ZnCl2 and H2 gas.
Zn + HCl → ZnCl2 + H2
(ii) Zn metal reacts with NaOH to produce sodium zincate NaZnO2 and hydrogen gas. Zn + NaOH → NaZnO2 + H2
(b) Ammonium chloride is formed by the reaction between the strong acid HCl and weak base NH4OH.
Hence ammonium chloride is acidic salt.
pH range of the salt is 4.6 to 6.0.
34. Write a chemical name of Na2CO3.10H2O and Na2CO3. Write the significance of 10H2O. Mention the term used for water molecules attached with a salt. With the help of the chemical equation, explain the method of preparation of both Na2CO3.10H2O and Na2CO3. Also, list two uses of Na2CO3.10H2O.
Ans. Na2CO3.10H2O is washing soda and its chemical name is hydrated sodium carbonate.
Na2CO3 is anhydrous sodium carbonate.
10H2O is the water of crystallisation is the fixed number of water molecules.
When NaHCO3 is heated it gives powder of Na2CO3 and when this powder is recrystallised to get Na2CO3.10H2O that has detergent properties.
NaHCO3 + Heat → Na2CO3 + H2O + CO2
Na2CO3 + 10H2O → Na2CO3.10H2O.
(Sodium carbonate)
Two uses of washing soda (Na2CO3.10H2O) are
i. It is used by doctors as plaster for supporting fractured bones in the right position.
ii. It is used as decorative in buildings.
35. (a) Mention the pH ranges within which our body works. Explain how antacid give relief from acidity? Write the name of one such antacid.
(b) Mention the nature of toothpaste.
Ans. (a) Our body works within the pH range of 7.0 to 7.8.
During indigestion, the stomach produces too much acid and this causes pain and irritation. To get relief from this pain, people use antacids which neutralise the excess acid. Magnesium hydroxide (Milk of magnesia), a mild base is an antacid.
(b) Toothpaste is generally basic. Bacteria present in the mouth produce acids by the degradation of sugar and food particles remaining in the mouth after eating for cleaning the teeth. We use toothpaste that can neutralise excess acid and prevent tooth decay.
36. (a) A metal compound X reacts with dilute H2SO4 to produce effervescence. The gas evolved extinguishes a burning candle. If one of the compound formed is calcium Sulphate, then what are X and the gas evolved? Also, write a balanced chemical equation for the reaction reach which occurred.
(b) Name one antacid. How does it help to relieve indigestion in the stomach
(c) A farmer treats the soil with quick lime or calcium carbonate. What is the nature of soil? Why does the farmer treat the soil with quicklime?
Ans. X is calcium carbonate reacts with sulphuric acid to produce calcium sulphate, carbon dioxide gas, and hydrogen gas.
CaCO3 + H2SO4 → CaSO4 + CO2 + H2.
(b) Magnesium hydroxide (Milk of magnesia), a mild base is an antacid.
During indigestion, the stomach produces too much acid and this causes pain and irritation. To get relief from this pain, people use antacids which neutralize the excess acid.
(c) The soil is acidic so the farmer treats the soil with quick lime or calcium carbonate. Quick lime or calcium carbonate is basic in nature and neutralize the acidic soli.
37. I. Write a balanced chemical equation only for the following chemical properties of acids:
(a) When an acid reacts with metal.
(b) When an acid reacts with metal bicarbonate
(c) When an acid reacts with a base.
II. Three solution A, B, C has pH values 5, 8 and 10 respectively. Among the three which solution has maximum hydrogen ion concentration? Classify the nature of the three solutions as acidic or basic.
Ans. (a) When an acid reacts with the metal to produce salt and hydrogen gas.
HCl + Na → NaCl + H2
(b) When an acid reacts with metal bicarbonate to produce salt, carbon dioxide gas and water.
H2SO4 + 2NaHCO3 → Na2SO4 + 2CO2 + 2H2O.
(c) When an acid reacts with a base to produce salt and water. This reaction is known as neutralisation reaction.
HCl + NaOH → NaCl H2O.
II. pH value of A is 5 which is less than 7 has a maximum value of H+ ions concentration.
pH = 5 means H+ = 10^-5 M/L concentration.
Solution A is acidic as pH value is less than 7 and solutions B and C are basic because they have pH vaue more than 7.
38. (a) Study the following chemical equation. CaSO4.2H2O→CaSO4.1/2H2O +3/2H2O.
Name the reactant and the product and mention one use of the product.
(b) The following salts are formed by the reaction of an acid with a base. Name the acids and base from which these salts are formed. Also mention the nature of the salt, whether it is acidic or basic.
(i) Sodium chloride
(ii) Ammonium nitrate.
Ans. (a) In the reaction, CaSO4.2H2O→CaSO4.1/2H2O +3/2H2O reactant is hydrated calcium sulphate and products are hemihydrate calcium sulphate and water.
(b) (i) Sodium chloride is formed by the reaction of hydrochloric acid with sodium hydroxide.
This salt is formed by the reaction between strong acid and strong base so it is neutral salt.
(ii) Ammonium nitrate is formed by the reaction of nitric acid with ammonium hydroxide. This salt is acidic salt.
This salt is formed by the reaction between strong salt and weak base so it is an acidic salt.
39. Under what soil condition do you think a farmer would treat the soil of these fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?
Ans. Plants require a specific pH range that is 5.5 to 7 for their healthy growth. A farmer would treat the soil of these fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate), when pH value of the soil is lower than 5.5 and soil becomes acidic. Calcium oxide neutralises the acid present in soil.
40. Five solutions A, B, C, D, and E, when tested with universal indicator, showed pH as 4, 1, 11, 7 and 9 respectively. Which solution is it?
(i) Neutral,
(ii) Strongly alkaline,
(iii) Strongly acidic,
(iv) Weakly acidic,
(v) Weakly alkaline.
Arrange the pH in increasing order of hydrogen-ion concentration.
Or
[Do yourself: (a) Explain why is hydrochloric acid a strong acid and acetic weak acid? How can it be verified?
(b) Explain why the aqueous solution of acid conduct electricity.
(c) You have 4 solutions A, B, C, D. The pH of solutions of A is 6, B is 9, C is 12 and D is 7,
(i) Identify the most acidic and most basic solution.
(ii) Arrange the above four solutions in the increasing order of H+ ion concentration.
(iii) State the change in colour of pH paper on dipping in solutions and D.]
Ans. (i) Solution D has pH value 7 hence it is neutral.
(ii) Solution C is strongly alkaline because it has the highest pH value which is more than 7.
(iii) B solution has pH value 1 which is the lowest value and hence it is a strong acid.
(iv) Solution A has pH value is less than 7 and more than B and so it is weakly acidic
(v) E solution has pH 9 that is more than 7 hence it is basic.
Ans. Na2CO3.10H2O (washing soda) is used for softening hard water.
39. CuSO4 crystal lose their blue colour and turn white when heated strongly, why?
Ans. Blue coloured copper sulphate crystals contain water of crystallization. When we heat the crystals, this water is removed and the salt turns white.
40. What is alkali? Give an example.
Ans. Alkali is a metallic oxide that is soluble in water. Examples - Na2O, CaO, etc.
40. What is alkali? Give an example.
Ans. Alkali is a metallic oxide that is soluble in water. Examples - Na2O, CaO, etc.
II. Short answer type questions:
1. Write the name of acids in the following:
(i) Tomato (ii) Vinegar (iii) Lemon (iv) Apple.
1. Write the name of acids in the following:
(i) Tomato (ii) Vinegar (iii) Lemon (iv) Apple.
Ans.
(i) Tomato contains -Oxalic acid.
(i) Tomato contains -Oxalic acid.
(ii) Vinegar contains - Acetic acid.
(iii) Lemon contains - Citric acid
(iv) Apple contains - Malic acid
2. A piece of zinc metal is dropped in a dilute solution of hydrochloric acid.
(a) Which gas is liberated when a metal reacts with an acid?
(b) How will you test the presence of this gas?
(c) Is it lighter or heavier than air?
(d) How will you collect the above gas?
Ans. (a) Hydrogen gas.
(b) Burning of hydrogen gas with a pop sound.
(c) It is lighter than air.
(d) By the process of displacement of water.
3. A white powder is added while baking bread and cakes to make them soft and fluffy. What is the name of the Powder? What are the main ingredients in it? What are the functions of each ingredient?
Ans. Baking powder is a white powder that is added while baking bread and cakes to make them soft and fluffy.
The main ingredients are sodium bicarbonate and tartaric acid. Sodium- bicarbonate helps bread or cake to rise to make them soft and spongy. Tartaric acid is a mild acid that helps to reduce the bitterness of baking soda.
4. Classify the following as acidic, basic, or neutral salts:
NaCl, KNO3, AlCl3, ZnSO4, CuSO4, CH3COONa, NaHCO3, Na2CO3.
NaCl, KNO3, AlCl3, ZnSO4, CuSO4, CH3COONa, NaHCO3, Na2CO3.
Ans. Acidic salt - , AlCl3, ZnSO4, CuSO4 .(These salts are formed by the reaction of strong acid and weak base.)
Basic salt - CH3COONa, NaHCO3, Na2CO3 (Salts are formed by the reaction of a strong base and weak acid).
Neutral salts - NaCl, ( Salts are formed by the reaction of strong acid and strong base).
5. Salt A commonly used in bakery products on heating gets converted into another salt B which itself is used for removal of hardness of water and a gas C is evolved. The gas C when passed through lime water, turns it milky. Identify A, B, and C.
Ans. A is the baking soda (sodium bicarbonate), used in bakery products.
B is the washing soda (sodium carbonate) used for removal of hardness of water and C is carbon dioxide gas when passed through lime water, turns it milky.
NaHCO3 + Heat → Na2CO3 + H2O + CO2.
(Sod.bicarbonate) (Sod. carbonate) (Water) (Carbon dioxide)
6. The solution of hydrochloric acid is added to the solution of sodium hydroxide solution containing phenolphthalein indicator dropwise. After some time the pink colour of the solution disappears.
(a) Identify the type of reaction
(b) Why the pink colour of the solution fades away after some time?
(b) Why the pink colour of the solution fades away after some time?
Ans. (a) It is the neutralization reaction.
(b) Phenolphthalein gives pink colour in a basic solution of sodium hydroxide and after neutralization reaction, the pink colour of the solution becomes colorless.
7. Name the acid and base used to form the following salts:
NaHCO3, ZnSO4, AlCl3.
NaHCO3, ZnSO4, AlCl3.
Ans. Carbonic acid is used in the formation of NaHCO3
Sulphuric acid is used in the formation of ZnSO4 and
Hydrochloric acid is used in AlCl3.
Sulphuric acid is used in the formation of ZnSO4 and
Hydrochloric acid is used in AlCl3.
8. A milkman adds a small amount of baking soda to fresh milk.
(a)Why does the milkman shift the pH of fresh milk is slightly alkaline?
(b)Why does the milk take a longer time to set as curd?
(a)Why does the milkman shift the pH of fresh milk is slightly alkaline?
(b)Why does the milk take a longer time to set as curd?
Ans. (a) Fresh milk contains lactose and has a pH value 6. Due to the fermentation of lactose by lactic bacteria lactose changes into lactic acids and milk changes into curd, that is why milkman shifts.
(b) Baking soda which is alkaline neutralizes excess acid in the milk and keeps the milk from becoming sour for a long time.
(b) Baking soda which is alkaline neutralizes excess acid in the milk and keeps the milk from becoming sour for a long time.
9. A green coloured hydrated metallic salt on heating, loss its water of crystallization and give the smell of burning sulphur. Identify the salt and write down the reaction involved.
Ans. A green coloured hydrated ferrous sulphate salt on heating, loss its water of crystallization and give the smell of burning sulphur.
Chemical equations to show the changes that occur when clean coloured ferrous sulphate crystals are heated-
Heat
FeSO4.7H2O → FeSO4 + 7H2O
Heat
2FeSO4 → Fe2O3 + SO2 + SO3
Ans. A green coloured hydrated ferrous sulphate salt on heating, loss its water of crystallization and give the smell of burning sulphur.
Chemical equations to show the changes that occur when clean coloured ferrous sulphate crystals are heated-
Heat
FeSO4.7H2O → FeSO4 + 7H2O
Heat
2FeSO4 → Fe2O3 + SO2 + SO3
10. While diluting an acid why is it recommended that the acid should be added to water and not water to the acid?
Ans. The process of dissolving an acid in water is a highly exothermic reaction. The acid must always be added slowly to water with constant stirring because water absorbs heat produced by the reaction. If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns. The glass container may also break due to excessive local heating.
Ans. The process of dissolving an acid in water is a highly exothermic reaction. The acid must always be added slowly to water with constant stirring because water absorbs heat produced by the reaction. If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns. The glass container may also break due to excessive local heating.
11. Dry HCl gas does not change the colour of dry blue litmus paper. Give reasons.
Ans. In the absence of water, HCl can not produce H3O+ ions which are responsible for acidic character. So dry HCl gas does not change the colour of dry litmus paper.
Ans. In the absence of water, HCl can not produce H3O+ ions which are responsible for acidic character. So dry HCl gas does not change the colour of dry litmus paper.
12. HCl and HNO3 show acidic characteristics in aqueous solution, while alcohol and glucose solutions do not. Give reason.
Ans. HCl and HNO3 produce H3O+ ions in the presence of water which is responsible for the acidic property but alcohol and glucose do not form hydronium ions so they do not show the acidic property.
Ans. HCl and HNO3 produce H3O+ ions in the presence of water which is responsible for the acidic property but alcohol and glucose do not form hydronium ions so they do not show the acidic property.
13. Name the gas evolved when sodium hydrogen carbonate is made to react with dilute hydrochloric acid. How will you test the gas?
Ans. When sodium-hydrogen carbonate reacts with hydrogen chloride it forms carbon dioxide gas with other product NaCl, water.
For the test of gas: When carbon dioxide gas is passed through the lime water, lime water turns milky due to the formation of CaCO3.
NaHCO3 + HCl → NaCl + H2O + CO2.
CO2 + Ca(OH)2 → CaCO3 + H2O.
Ans. When sodium-hydrogen carbonate reacts with hydrogen chloride it forms carbon dioxide gas with other product NaCl, water.
For the test of gas: When carbon dioxide gas is passed through the lime water, lime water turns milky due to the formation of CaCO3.
NaHCO3 + HCl → NaCl + H2O + CO2.
CO2 + Ca(OH)2 → CaCO3 + H2O.
14. A substance X, which is an oxide of metal is used intensively in the cement industry. This element is present in bones also. On treatment with water, it forms a solution that turns red litmus blue. Identify X and also write the equation for its chemical reactions with water.
Ans. X is calcium oxide CaO.
Chemical equation: When calcium oxide reacts with water to form calcium hydroxide solution that turns red litmus to blue.
CaO + H2O ➝ Ca(OH)2
Ans. X is calcium oxide CaO.
Chemical equation: When calcium oxide reacts with water to form calcium hydroxide solution that turns red litmus to blue.
CaO + H2O ➝ Ca(OH)2
15. How will you prove that a given salt is a carbonate of metal?
Ans. When carbonate metal is heated it forms a gas. When this gas is passed through the lime water it turns the lime water to milky then this gas is CO2 which can be formed by the heating of carbonate metal.
XCO3 + heat ➝ XO + CO2.
16. You might have seen lemon or tamarind juice being used to clean the tarnished surface of copper vessels. Explain why these sour substances are effective in cleaning the vessels?
Ans. When copper vessels come in contact with air it reacts with CO2 and water vapour to forms a green layer of CaCO3.Ca(OH)2 which is basic in nature. So to neutralise this basic layer, lemon or tamarind juice which contains acid being used to clean the tarnished surface of copper vessels.
Ans. When carbonate metal is heated it forms a gas. When this gas is passed through the lime water it turns the lime water to milky then this gas is CO2 which can be formed by the heating of carbonate metal.
XCO3 + heat ➝ XO + CO2.
16. You might have seen lemon or tamarind juice being used to clean the tarnished surface of copper vessels. Explain why these sour substances are effective in cleaning the vessels?
Ans. When copper vessels come in contact with air it reacts with CO2 and water vapour to forms a green layer of CaCO3.Ca(OH)2 which is basic in nature. So to neutralise this basic layer, lemon or tamarind juice which contains acid being used to clean the tarnished surface of copper vessels.
17. Though the compounds such as glucose and alcohol have hydrogen atom in their molecules yet they are not categorized as acids. Why?
Ans. Glucose and alcohol have hydrogen atom in their molecules yet they are not categorized as acids as they do not produce hydronium ions which are responsible for showing the acidic property.
Ans. Glucose and alcohol have hydrogen atom in their molecules yet they are not categorized as acids as they do not produce hydronium ions which are responsible for showing the acidic property.
18. State the chemical name of the Plaster of Paris. Write a chemical equation to show the reaction between the Plaster of Paris and water.
Ans. The chemical name of the Plaster of Paris is hemihydrate Calcium Sulphate.
When the Plaster of Paris reacts with water, it changes to gypsum and forms a hard solid mass.
CaSO4 .1/2 H2O + 1 1/2 H 2O → CaSO4 .2H 2O
(Plaster of Paris) (Gypsum)
Ans. The chemical name of the Plaster of Paris is hemihydrate Calcium Sulphate.
When the Plaster of Paris reacts with water, it changes to gypsum and forms a hard solid mass.
CaSO4 .1/2 H2O + 1 1/2 H 2O → CaSO4 .2H 2O
(Plaster of Paris) (Gypsum)
19. What is the colour of FeSO4 crystals? How does this colour change upon heating? Give a balanced chemical equation for the changes.
Ans. The colour of FeSO4 crystals is green. When FeSO4 crystals are heated its colour becomes white due to the loss of water molecules by the evaporation.
The chemical reaction is:
FeSO4 .10 H2O+ Heat → FeSO4 + H2O
Ans. The colour of FeSO4 crystals is green. When FeSO4 crystals are heated its colour becomes white due to the loss of water molecules by the evaporation.
The chemical reaction is:
FeSO4 .10 H2O+ Heat → FeSO4 + H2O
20. Classify the following salts into acidic, basic and neutral: Potassium Sulphate, ammonium chloride, sodium carbonate, sodium chloride.
Ans. Potassium Sulphate is a neutral salt because this salt is formed by the reaction between strong acid (H2SO4) and a strong base (KOH).
Ammonium Chloride is an acidic salt because this salt is formed by the reaction between strong acid (HCl) and weak base (NH3OH).
Sodium carbonate is a basic salt because this salt is formed by the reaction between weak acid (H2CO3) and strong base (NaOH).
Ans. Potassium Sulphate is a neutral salt because this salt is formed by the reaction between strong acid (H2SO4) and a strong base (KOH).
Ammonium Chloride is an acidic salt because this salt is formed by the reaction between strong acid (HCl) and weak base (NH3OH).
Sodium carbonate is a basic salt because this salt is formed by the reaction between weak acid (H2CO3) and strong base (NaOH).
21. Write chemical equations that show Aluminium oxide reacts with acid as well as a base.
Ans. When aluminium oxide reacts with an acid HCl to form aluminium chloride salt and water.
Al2O3 + 6HCl → 2AlCl3 + 3H2O
When aluminium oxide reacts with a base Ca(OH)2 to form sodium aluminate salt and water.
Al2O3 + NaOH→ NaAl2O3 + 3H2O.
Ans. When aluminium oxide reacts with an acid HCl to form aluminium chloride salt and water.
Al2O3 + 6HCl → 2AlCl3 + 3H2O
When aluminium oxide reacts with a base Ca(OH)2 to form sodium aluminate salt and water.
Al2O3 + NaOH→ NaAl2O3 + 3H2O.
22. Crystal of a substance changed their colour on heating in a closed vessel but regained after some time, when they were allowed to cool down.
(a) Name one such substance (b) Explain the phenomenon involved.
Ans. (a) Copper Sulphate Crystal- (CuSO4.5H2O).
(b) Hydrated copper sulphate crystals that seem to be dry contain 5 molecules water of crystallisation. When we heat the crystals, its water turns into water vapour and the colour of the crystals turns blue to white. When they were allowed to cool down the water vapour condenses to water and mixes with this crystal which causes the colour of the crystal to return.
This type of salt is called hygroscopy.
(a) Name one such substance (b) Explain the phenomenon involved.
Ans. (a) Copper Sulphate Crystal- (CuSO4.5H2O).
(b) Hydrated copper sulphate crystals that seem to be dry contain 5 molecules water of crystallisation. When we heat the crystals, its water turns into water vapour and the colour of the crystals turns blue to white. When they were allowed to cool down the water vapour condenses to water and mixes with this crystal which causes the colour of the crystal to return.
This type of salt is called hygroscopy.
23. (a) How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted?
(b) How is the concentration of hydroxide ions (OH-) affected when excess base is dissolved in water?
Ans. (a) When an acid is diluted with water results in a decrease in the concentration of ions (H3O+) per unit volume.
(b) How is the concentration of hydroxide ions (OH-) affected when excess base is dissolved in water?
Ans. (a) When an acid is diluted with water results in a decrease in the concentration of ions (H3O+) per unit volume.
(b) When the excess base is dissolved in water, the concentration of (OH-) ions per unit volume in the solution increases.
24. What is meant by the term pH of the solution? The pH of rainwater collected from two cities A and B was found to be 6 and 5 respectively. The water in which the city is more acidic?
Ans. A scale for measuring hydrogen ion concentration in a solution which indicates the acidic or basic nature of a solution, called pH scale. pH should be thought of simply as a number. Higher the hydronium ion concentration, lower is the pH value.
pH of city B is less than the city A so the B city is more acidic.
pH of city B is less than the city A so the B city is more acidic.
25. Explain and write the chemical formula of baking soda. How is baking soda prepared?
Ans. The chemical name of the baking soda is sodium hydrogen carbonate (NaHCO3). It is produced by the using of sodium chloride as one of the raw materials.
NaCl + H2O + CO2 + NH3 →NH4Cl + NaHCO3
(Sodium chloride) (Ammonium hydrogen carbonate)
26. What is a neutralization reaction? Give two examples.
Ans. The reaction between an acid and a base to give a salt and water is known as a neutralization reaction.
A neutralization reaction can be written as –
Base + Acid → Salt +Water
Two examples are:
i. When sodium hydroxide reacts with hydrochloric acid to form sodium chloride and water.
NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
ii. When potassium hydroxide reacts with sulphuric acid to forms potassium sulphate and water.
KOH + H2SO4 → K2SO4 + H2O.
Ans. The reaction between an acid and a base to give a salt and water is known as a neutralization reaction.
A neutralization reaction can be written as –
Base + Acid → Salt +Water
Two examples are:
i. When sodium hydroxide reacts with hydrochloric acid to form sodium chloride and water.
NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
ii. When potassium hydroxide reacts with sulphuric acid to forms potassium sulphate and water.
KOH + H2SO4 → K2SO4 + H2O.
27. A knife which is used to cut fruit, was immediately dipped into water containing drugs or blue Litmus solution if the colour of the solution is changed to red what inference can be drawn about the nature of the fruit? And why?
Ans. I. The fruit contains acid so when the knife which is used to cut fruit, was immediately dipped into water containing blue Litmus solution, the colour of the solution is changed to red because when blue litmus solution comes in contact with acid its colour changes to red.
28. The colour of copper sulphate solution changes when an iron nail is dipped in it. State the reason-giving the chemical equation for the reaction involved.
Ans. The blue colour of copper sulphate solution changes to green colour when an iron nail is dipped as Fe is more reactive than copper and Fe displaces Cu from its solution and formed iron sulphate which is green in colour.
Ans. I. The fruit contains acid so when the knife which is used to cut fruit, was immediately dipped into water containing blue Litmus solution, the colour of the solution is changed to red because when blue litmus solution comes in contact with acid its colour changes to red.
28. The colour of copper sulphate solution changes when an iron nail is dipped in it. State the reason-giving the chemical equation for the reaction involved.
Ans. The blue colour of copper sulphate solution changes to green colour when an iron nail is dipped as Fe is more reactive than copper and Fe displaces Cu from its solution and formed iron sulphate which is green in colour.
CuSO4 + Fe → Cu + FeSO4.
29. What are strong acid or base and weak acid or base?
Ans. A strong acid is an acid that ionizes completely in a solution of water and gives H+ ions and a weak acid is an acid that ionizes incompletely in a solution of water.
A strong base is a base that ionizes completely in a solution of water and gives -OH ions and a weak base is a base that ionizes completely in a solution of water.
Ans. A strong acid is an acid that ionizes completely in a solution of water and gives H+ ions and a weak acid is an acid that ionizes incompletely in a solution of water.
A strong base is a base that ionizes completely in a solution of water and gives -OH ions and a weak base is a base that ionizes completely in a solution of water.
30. A compound that is prepared from gypsum has the property of hardening when mixed with the proper quantity of water. Identify the compound and write its chemical formula.
Ans. Plaster of Paris is a compound that is prepared from gypsum and plaster of Paris has the property of hardening when mixed with the proper amount of water.
The chemical formula of plaster of Paris - CaSO4.1/2H2O.
Ans. Plaster of Paris is a compound that is prepared from gypsum and plaster of Paris has the property of hardening when mixed with the proper amount of water.
The chemical formula of plaster of Paris - CaSO4.1/2H2O.
31. Give chemical equations to show the changes that occur when clean coloured ferrous sulphate crystals are heated. Mention the change observed as well as the reason for this change.
Ans. Chemical equations to show the changes that occur when clean coloured ferrous sulphate crystals are heated-
Heat
FeSO4.7H2O → FeSO4 + 7H2O
Heat
2FeSO4 → Fe2O3 + SO2 + SO3
On heating, it loses the seven molecules of water of crystallization and forms anhydrous ferrous sulphate, which is greenish-white in colour. When anhydrous ferrous sulphate is further heated, it decomposes to give ferric oxide (Fe2O3), sulphur dioxide, and sulphur trioxide which is reddish-brown in colour.
Ans. Chemical equations to show the changes that occur when clean coloured ferrous sulphate crystals are heated-
Heat
FeSO4.7H2O → FeSO4 + 7H2O
Heat
2FeSO4 → Fe2O3 + SO2 + SO3
On heating, it loses the seven molecules of water of crystallization and forms anhydrous ferrous sulphate, which is greenish-white in colour. When anhydrous ferrous sulphate is further heated, it decomposes to give ferric oxide (Fe2O3), sulphur dioxide, and sulphur trioxide which is reddish-brown in colour.
32. The plaster of Paris should be stored in a moisture-proof container. Why?
Ans. Plaster of Paris is a white powder and when it comes in contact with water vapour present in the atmosphere, it changes to gypsum giving a hard solid mass. Hence to avoid this it should be stored in a moisture-proof container.
33. Write the chemical formula of bleaching powder. Write a balanced chemical equation involved in the preparation of bleaching powder.
Ans. The chemical formula of bleaching powder is CaOCl2.
Bleaching powder is produced by the action of chlorine on dry slaked lime Ca(OH)2.
Ca(OH)2 + Cl2 → CaOCl2 + H2O.
Ans. Plaster of Paris is a white powder and when it comes in contact with water vapour present in the atmosphere, it changes to gypsum giving a hard solid mass. Hence to avoid this it should be stored in a moisture-proof container.
33. Write the chemical formula of bleaching powder. Write a balanced chemical equation involved in the preparation of bleaching powder.
Ans. The chemical formula of bleaching powder is CaOCl2.
Bleaching powder is produced by the action of chlorine on dry slaked lime Ca(OH)2.
Ca(OH)2 + Cl2 → CaOCl2 + H2O.
III. Long answer type questions:
1. White hydrated salt of sodium is used for removing permanent hardness from water.
(a) Write the chemical name and formula of the salt.
(b) Write the steps of preparation of the salt.
(c) Mention one domestic use and one industrial use of the compound.
(a) Write the chemical name and formula of the salt.
(b) Write the steps of preparation of the salt.
(c) Mention one domestic use and one industrial use of the compound.
Ans. (a) Hydrated sodium carbonate - Na2CO3.10H2O is used for removing the hardness of the water.
(b) In the 1st step sodium hydrogen carbonate prepared by the reaction of sodium chloride with water, carbon dioxide, and ammonia.
In the second step, sodium hydrogen carbonate heated and produces sodium carbonate.
In the third step - recrystallization of sodium carbonate gives washing soda.
(c) Sodium carbonate can be used as a cleaning agent for domestic purposes.
Sodium carbonate (washing soda) is used in glass, soap and paper industries.
2. In one of the industrial process for the manufacture of sodium hydroxide, a gas X is formed as a by-product. The gas X reacts with lime water to give a compound Y which is used as a bleaching agent in the chemical industry. Identify X and Y giving the chemical equation of the reaction involved.
Ans. In the industrial process which is the Chlor alkali process for the manufacture of sodium hydroxide, chlorine gas is formed as a by-product. The chlorine gas reacts with lime water to give a calcium oxychloride which is used as a bleaching agent in the chemical industry.
Therefore X is chlorine gas and Y is calcium oxychloride CaOCl2.
Reaction is :
Chlor-alkali process in which NaCl react with water to produce NaCl, Cl2 and H2 gas.
2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2(g) + H2(g)
Ca(OH)2 + Cl2 → CaOCl2 + H2O
3. Comment on the following :
(i) An acid reacts with substance X produces a gas that burns with a pop sound. What is the nature of X?
(ii) An acid when reacting with Z produces CO2 gas. What can be Z?
(iii) CaO and SO2 are two oxides. Name the oxide which will base?
(iv) A sodium compound is used for removing the permanent hardness of the water. Name the compound.
(v) A substance on treatment with chlorine gas yields bleaching powder. Name the substance.
Ans. (i) X is a metal that reacts with acid and produces hydrogen gas that burns with a pop sound.
(ii) Z is a carbonate compound that reacts with an acid to produce as a byproduct CO2 gas.
(iii) CaO is a basic oxide.
(iv) Hydrated sodium carbonate - Na2CO3.10H2O.
(v) Calcium hydroxide- Ca(OH)2.
4. What will be the action of the following substances on litmus paper?
(i) Dry HCl gas.
(ii) Moistened NH3
(iii) Lemon juice.
(iv) Carbonate soft drink
(v) Curd
(vi) Soap solution.
(i) Dry HCl gas.
(ii) Moistened NH3
(iii) Lemon juice.
(iv) Carbonate soft drink
(v) Curd
(vi) Soap solution.
Ans. (i) Dry HCl gas does not change the colour of the litmus paper due to the absence of hydronium ions.
(ii) Moistened NH3 is NH4OH is a base and it changes the colour of red litmus to blue.
(iii) Lemon juice is a citric acid and it changes the colour of blue litmus to red.
(iv) Carbonate soft drink contains carbonic acid and turns blue litmus to red.
(v) Curd contains lactic acid os it changes the colour of blue litmus to red.
(vi) Soap solution is a basic solution and it changes the colour of the red litmus to blue.
5. I.Name the acid present in ant stings and gives its chemical formula. Also, give the common method to get relief from the discomfort caused by the ant sting. Write the colour of the following indicators in acid, base and neutral solution:
(i) Litmus
(ii) Phenolphthalein
(iii) Methyl orange (iv)Turmeric juice.
II. When 1 drop of orange juice is added to pure water how the pH value will vary for water? If one drop of lemon juice is also added, will there be any more change in the pH value?
(i) Litmus
(ii) Phenolphthalein
(iii) Methyl orange (iv)Turmeric juice.
II. When 1 drop of orange juice is added to pure water how the pH value will vary for water? If one drop of lemon juice is also added, will there be any more change in the pH value?
Ans. I. Formic acid is present in ant stings and its chemical formula is HCOOH.
Bases neutralise acids so baking soda which is a basic in nature is used to get relief from discomfort caused by the ant sting which contains acids.
(I) Colour of blue litmus changes to red.
(ii) Remains colourless.
(iii) Orange to pink.
(iv) Yellow to red.
II. Orange juice is an acid when 1 drop of orange juice is added to pure water the pH value will be decreasing for water and if one drop of lemon juice which is also acid, is also added, there will be more change in the pH value that is decreasing.
Bases neutralise acids so baking soda which is a basic in nature is used to get relief from discomfort caused by the ant sting which contains acids.
(I) Colour of blue litmus changes to red.
(ii) Remains colourless.
(iii) Orange to pink.
(iv) Yellow to red.
II. Orange juice is an acid when 1 drop of orange juice is added to pure water the pH value will be decreasing for water and if one drop of lemon juice which is also acid, is also added, there will be more change in the pH value that is decreasing.
6. A metal carbonate X on reacting with acid gives a gas which when passed through a solution Y gives the carbonate back. On the other hand, a gas G that is obtained at the anode during electrolysis of brine is passed on dry Y, it gives a compound Z, used for disinfecting drinking water. Identify X, Y, G, and Z .
Ans. When sodium carbonate reacts with acid gives carbon dioxide gas which when passed through a calcium hydroxide solution gives the carbonate back. On the other hand, chlorine gas is obtained at the anode during electrolysis of brine is passe on dry calcium hydroxide, it gives a compound calcium oxychloride, used for disinfecting drinking water.
Therefore X is sodium carbonate NaCO3, Y is calcium hydroxide Ca(OH)2, G is chorine gas Cl2 gas and Z is calcium oxychloride known as bleaching powder CaOCl2.
Therefore X is sodium carbonate NaCO3, Y is calcium hydroxide Ca(OH)2, G is chorine gas Cl2 gas and Z is calcium oxychloride known as bleaching powder CaOCl2.
7. For the baking cake, baking powder is taken. If at home you have backing soda instead of baking powder:
(i) How will it affect the test of the cake?
(ii) How can baking soda be converted into baking powder?
(iii) What is the role of tartaric acid added to baking soda?
Ans. (I) Baking powder is a base and bitter in the test so the test of cake becomes slightly bitter.
(ii) Baking soda can be converted into baking powder by adding mild edible acid such as tartaric acid. Tartaric acid is present in tamarind which reduces the bitter test of the baking soda.
(iii) Tartaric acid reduces the bitterness of cake baking soda is a base and bitter in the test so tartaric acid reacts with baking soda and neutralise the bitter test.
8. What is bleaching powder? How is it prepared? list two uses of bleaching powder.
Or
[Do your self: (a) Write the common name of CaOCl2 How is it prepared. Write the chemical equation of the reaction involved in the process. Give any two uses of it.
(b) Write the chemical name of washing soda. How is it prepared? Give the relevant chemical equation.]
Ans. Bleaching powder is a salt, calcium oxychloride ( CaOCl2,).
Preparation of CaOCl2: chlorine is produced by the electrolysis of aqueous sodium chloride (brine). This chlorine gas is used or the manufacture of bleaching powder. Bleaching powder is produced by the action of chlorine on dry slaked lime Ca(OH)2.
Ca(OH)2 + Cl2 → CaOCl2 + H2O
(i) It is used for disinfecting drinking water to make it free of germs.
(ii) It is used for bleaching cotton, linen, wood pulp, washed clothes in the laundry and
(ii) It is used as an oxidising agent in many chemical industries.
9. (a) What would be the colour of the solution when copper oxide and dilute hydrochloric acid are mixed?
(b) Write a chemical equation that represents that the effect of a base is nullified by an acid and vice versa.
Ans. (a) The colour of the solution becomes blue-green when copper oxide and dilute hydrochloric acid are mixed.
When copper oxide reacts with hydrochloric acid to produces copper chloride and water.
CuO + HCl → CuCl2 + H2O
(blue green)
(b) When hydrochloric acid reacts with base sodium hydroxide it formes a neutral salt and water. This reaction is known as neutralisation reaction. In this reaction both acid and base netralises each other.
NaOH + HCl → NaCl + H2O
10. A dry pellet of a common base B, when kept in open absorbs moisture and turns sticky. The compound is also a by-product of Chlor- alkali process Identify B. What type of reactions occurs when B is treated with an acidic oxide.
Ans. A dry pellet of a common base B is sodium hydroxide NaOH, when kept in open absorbs moisture and turns sticky. NaOH is a by-product of chlor- alkali process.
Chlor-alkali process:
NaCl + H2O → NaOH + Cl2 + H2
When sodium hydroxide which is a base reacts with acidic oxide solution like CO2 which is acidic in nature, produces salt and water and this type of reaction is called neutralisation reaction.
NaOH + CO2 → NaCO3+ H2O
11. Write the chemical formula of the following salt and obtained from which acid or base:
(i) Ammonium chloride. ( ii) Copper Sulphate
(iii) Sodium chloride (iv) Magnesium Nitrate
(v) Potassium Sulphate. (vi) Calcium nitrate.
Ans. (i) Ammonium Chloride - NH4Cl
Acid - HCl, Base - NH4OH
(ii) Copper Sulphate - CuSO4.
Acid - H2SO4, Base - Cu(OH)2.
(iii) Sodium Chloride - NaCl
Acid - HCl, Base - NaOH
(iv) Magnesium Nitrate - Mg(NO3)2
Acid - HNO3, Base - Mg(OH)2
(v) Potassium Sulphate - K2SO4
Acid - H2SO4, Base - KOH
(vi) Calcium Nitrate- Ca(NO3)2
Acid - HNO3, Base Ca(OH)2.
12. While constructing a house a builder select marble flooring and marble tabletop for the kitchen where vinegar, juices of lemon, and tamarind, etc. are more often used for cooking. Will you agree to this selection and why?
Ans. Vinegar, juices of lemon, and tamarind, etc. are contain acetic acids, citric acid and tarteric acid. These acids can react with marble which is calcium carbonate. So when accidentally these acids fall on the floor of the marble, marble rapidly reacts with these acids and causes a chemical reaction and marble can be damaged.
So I will not agree with this selection.
13. A white powder A is the mild non-corrosive base and is used in the preparation of cakes. When the powder A is heated it gives another powder B.The powder B is recrystallized to get a substance C that has detergent properties. Identify A, B, and C and also write balanced chemical equations for the conversions of A to B and then B to C.
Ans. NaHCO3 is the mild non-corrosive base and is used in the preparation of cakes. When NaHCO3 is heated it gives powder of Na2CO3 and when this powder is recrystallised to get Na2CO3.10H2O that has detergent properties.
Therefore A is sodium bicarbonate NaHCO3, B is sodium carbonate Na2CO3, and C is hydrated sodium carbonate Na2CO3.10H2O.
2NaHCO3 + Heat → Na2CO3 + H2O + CO3
(Sodium (Sodium carbonate)
hydrogen carbonate)
Na2CO3 + 10H2 O → Na2CO3.10H2O
( Washing soda)
14. A substance is used as an antacid reacts with hydrochloric acid to produce a gas Y which is used in extinguishing the fire.
(a) Name the substance X and gas Y.
(b) Write a balanced chemical equation of the reaction between X and hydrochloric acid.
Ans. Sodium bicarbonate NaHCO3 is an antacid reacts with hydrochloric acid HCl to produce a gas CO2 which is used in extinguishing the fire.
(a) X is NaHCO3 and Y is CO2 gas.
(b) A balanced chemical equation of the reaction between NaHCO3 and hydrochloric acid :
When sodium bicarbonate reacts with hydrochloric acid to produce sodium chloride water and carbondioxide gas.
2NaHCO3 + HCl → NaCl + H2O + CO3
15.(a) Write the name given to bases that are highly soluble in water. Give an example.
(b) How is tooth decay related to pH? How can it be prevented?
(c) Why does bee-sting cause pain and irritation? Rubbing of baking soda on the sting area gives relief. How?
Ans. (a) Sodium hydroxide, potassium hydroxide calcium hydroxide. etc are highly soluble in water.
(b) Tooth decay starts when the pH of the mouth is lower than 5.5. Tooth enamel does not dissolve in water but is corroded when the pH in the mouth is below 5.5. Bacteria present in the mouth produce acids by the degradation of sugar and food particles remaining in the mouth after eating.
The best way to prevent this is to clean the mouth after eating food. Using toothpaste, which is generally basic, for cleaning the teeth can neutralize the excess acid and prevent tooth decay.
(c) Bee-sting leaves an acid which causes pain and irritation. The use of a mild base like baking soda on the stung area gives relief.
16. I. Differentiate between strong and weak acids. Identify the strong and weak acids from the following list of acids: hydrochloric acid, acetic acid, formic acid, nitric acid.
II. What is meant by the term hydrated salt? Give two examples of hydrated salt which are white and state their chemical formula.
Ans. I. The strength of acids depends on the number of H+ ions produced.
Strong acids are acids that are completely dissociated and give rise to more H+ ions and weak acids are acids that do not completely dissociate or partially dissociate and gives to rise less H + ions.
Nitric acid and hydrochloric acid are strong acids.
Formic acid is a weak acid.
II. Hydrated salt is the salt that contains water of crystallisation which is the fixed number of water molecules in one formula unit of salt.
Example two hydrated salts are:
i. Plaster of Paris that is hemihydrate calcium sulphate which contains half molecules of water- CaSO4 .1/2 H2O
ii. Washing soda that is hydrated sodium carbonate which contains ten molecules of water - Na2CO3.10H2O.
17. A compound which is prepared from gypsum has the property of hardening when mixed with the right quantity of water.
(a) Identify the compound and write its chemical formula.
(b) Write the chemical equation for its preparation.
(c) List any two uses of the above compound.
Ans. (a) The plaster of Paris is prepared from gypsum and it becomes hard when mixed with the proper quantity of water.
(b) At 373 K, on heating gypsum, it loses water molecules and becomes hemihydrate calcium sulphate (CaSO4 .1/2 H2O) which is known as Plaster of Paris.
2CaSO4.2H2O + Heat → 2CaSO4.1/2H2O + 3H2O
(c) i. It is used by doctors as plaster for supporting fractured bones in the right position.
ii. It is used as decorative in buildings.
18. A student dropped a few pieces of marble in dilute hydrochloric acid contained in a test tube the evolved gas was then passed through lime water, what change would be observed in lime water? What will happen if excess of gas is passed through lime water?
Ans. When a student drops a few pieces of marble in dilute hydrochloric acid contained in a test tube the carbon dioxide gas evolved. When CO2 gas passed through lime water, lime water turns milky due formation of white precipitate CaCO3.
On passing the carbon dioxide gas evolved through lime water:
Ca(OH)2 (aq)+ CO2 (g)⟶ CaCO3(s) + H2O(l)
(Lime water) (White precipitate)
If an excess of gas is passed through the lime water then colourless soluble calcium bicarbonate is formed.
CaCO3(s) + H2O(l) + CO2 (g) → C(HCO3)2(aq)
19. I. You are given two solutions A and B. The pH of solution A is 6 and pH of solution B is 8
(a) Identify the acidic and basic solutions.
(b) Which solution has more H+ ion concentration? Give reasons for your answer.
II Why is HCl a stronger acid than acetic acid? Explain.
Ans. I. (a) pH value of A is less than 7 so it is an acidic solution and pH value of B is more than 7 so it is a basic solution.
(b) Solution A has more H+ ion concentration.
Reason: When pH value is 6 means the power of hydrogen is 6.
And the concentration of H+ ion is equal to 10^-6 Mol/L
For B pH is 8 and the concentration of H+ ion is equal to 10^-8 Mol/L
10^-8 < 10^-6
Therefore B has less H+ ion concentration.
II. Hydrochloric acids give more H+ ions by completely dissociation so they are said to be strong acids, and acetic acids give less H+ ions by partial dissociation so they are said to be weak acids.
[Note: To find the concentration of H+ : If pH = 7 = 7 x 1 = 7log10=log10^7 = log 1/10^-7 [log10 = 1]....1
And pH= log10 1/[H+]....2
Given pH=7
From eq. 1 & 2 we get
-log[H+] = log10^-7
H+ = 10^-7]
20. When a concentrated aqueous solution of substance X is electrolyzed, then NaOH, Cl2 and H2 are produced.
(a) Name the substance X
(b) What is the special name of this process and why is it so-called?
(c) Which gas is liberated at the anode? List one uses of this process.
Ans. (a) X is sodium chloride (NaCl) called brine.
When a concentrated aqueous solution of NaCl is electrolyzed, then NaOH, Cl2 and H2 are produced.
2NaCl + 2H2O → 2NaOH + Cl2 + H2
(b) This process is known as Chlor-alkali process because of the products formed– chlor for chlorine and alkali for sodium hydroxide.
(c) Chlorine Cl2 is liberated at the anode. This process is used for the manufacture of bleaching powder.
21. What is the chloralkali process? Why is it so-called? Write the equation for the reaction.
Name the three products of the chlor-alkali process. Write one commercially or industrially important material is that can be prepared from each of these products.
Ans. When electricity is passed through an aqueous solution of sodium chloride (called brine), it decomposes to form sodium hydroxide. This process is called the chlor-alkali process.
This process is called the chlor-alkali process because of the products formed– chlor for chlorine and alkali for sodium hydroxide.
2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2(g) + H2(g)
Ca(OH)2 + Cl2 → CaOCl2 + H2O.
The three products produced in this process are:
Chlorine gas Cl2 is formed at the anode, hydrogen gas at the cathode, and sodium hydroxide solution is formed near the cathode.
Uses of these three products:
.Chlorine gas is used for water treatment, in the manufacture of bleaching powder etc.
. NaOH is used for the manufacture of soaps and detergent, paper making, artificial fibers etc.
. Hydrogen gas H2 is used as fuels, margarine, for the preparation of ammonia for fertilizers etc.
The three products produced in this process are:
Chlorine gas Cl2 is formed at the anode, hydrogen gas at the cathode, and sodium hydroxide solution is formed near the cathode.
Uses of these three products:
.Chlorine gas is used for water treatment, in the manufacture of bleaching powder etc.
. NaOH is used for the manufacture of soaps and detergent, paper making, artificial fibers etc.
. Hydrogen gas H2 is used as fuels, margarine, for the preparation of ammonia for fertilizers etc.
22. "Sodium hydrogen carbonate is a basic salt "Justify the statement. How is it converted into washing soda? Explain.
Ans. : Basic salt is a salt produced by the reaction between a strong acid and a weak base. Sodium hydrogen carbonate produced by the reaction between a strong base (NaOH) and a weak acid (H2CO3), so it is a basic salt.
NaOH + H2CO3 → NaHCO3 + H2O
Sodium hydrogen carbonate is heated strongly to produce sodium carbonate.
NaHCO3 + Heat → Na2CO3 + H2O + CO2
Na2CO3 + 10H2O → Na2CO3.10H2O.
(Sodium carbonate)
23. There are three test tubes A, B, C. Test tube A has an acidic solution, test tube B has a basic solution and test tube C has distilled water. Identify the contents of each test tube with the help of litmus paper.
Ans. Test tube A has an acidic solution. Therefore the colour of blue litmus paper changes to red and the colour of red litmus paper does not bring out any change in the solution.
Test tube B has a basic solution. Therefore the colour of red litmus paper changes to blue in the solution and the colour of blue litmus paper does not bring out any change in the solution.
Test tube C has distilled water. Hence the solution is neutral so it does not bring out any change in the colour of litmus paper.
24. A liquid has a pH of less than 7 which is represented as an acidic solution.
(a) State the nature of the solution if its pH increases from 7 to 14.
(b) Mention the ion concentration increases with an increase in pH value.
(c) Suggest a method that is generally used for measuring PH value.
Ans. (a) As the pH value increases from 7 to 14, that is an increase in the strength of alkali.
(b) As the pH value increases, it represents an increase in (OH–) ion concentration and decreases in H+ ion concentration in the solution.
(c) The method that is generally used for measuring PH value is:
pH= - log10 [H+]
25. A few crystals of copper Sulphate is heated in a dry boiling tube:
(a) What is the colour before and after heating?
(b) What is the reason for the colour change?
(c) Can its original colour be restored? How?
Ans. (a) The colour of copper Sulphate before heating is blue due to the presence of crystal of water molecules.
(b) When we heat the crystals of hydrated copper sulphate, its water turns into water vapour and hydrated copper sulphate converted into anhydrous copper sulphate. so the colour of the crystals turns blue to white-grey in colour .
CuSO4.5H2O + Heat → CuSO4 + 5.H2O
(c) yes, its original colour can be restored by cooling and adding water.
Anhydrous copper sulphate converted into hydrated copper sulphate which is blue in colour.
CuSO4 + 5.H2O → CuSO4.5H2O
26. I.Giving reasons for each state which of the following will conduct electricity and which will not :
(a) A solution of glucose
(b) Dilute hydrochloric acid?
II.(a) If acetic acid and hydrochloric acid of the same concentration are taken, which of the two is stronger acid and why?
(b) How is the strength of an acid affected when some water is added to it?
Ans. (a) A solution of glucose does not conduct electricity because the electric current is carried through the solution by ions and glucose does not contain ions in solution.
(b) Dilute hydrochloric acid conduct electricity because it contains cation H+ which is responsible for conduct electricity.
II. (a) Hydrochloric acid is stronger than acetic acid of the same concentration because it completely dissociates into ions but acetic acid does not.
(b) When some water is added to an acid, results in a decrease in the concentration of ions (H3O+) per unit volume and the acid is said to be diluted. Hence the strength of an acid is decreased.
27. I. While eating food, you happen to spill some curry on your white shirt. You immediately scrub with soap. What happens to its yellow colour? What happens to this stain when the shirt is washed with plenty of water?
II. (a) Write the chemical formula of plaster of Paris and Gypsum.
(b) How can plaster of Paris be converted into gypsum?
(c) List anyone uses of plaster of Paris.
Ans. I. Curry contains turmeric which is yellow in colour and is a natural indicator for the base. When the shirt is scrubbed with soap which is a base, react with the turmeric present in the curry to form a reddish colour substance in the shirt, so the colour of yellow on the shirt becomes red.
When the shirt is washed with plenty of water its reddish colour substance removed and the colour of the stain becomes yellow.
II. (a) The chemical formula of plaster is Hemi hydrated calcium sulphate. CaSO4.1/2H2O
(b) When plaster of Paris mixed with the proper amount of water is converted into a hard mass of gypsum CaSO4.2H2O.
CaSO4.1/2H2O + CaSO4.2H2O.
(c) It is used by doctors as plaster for supporting fractured bones in the right position.
28. Rahul has been stung by the honey bee and is in great pain.
(a) What could be the reason for this burning pain? State the type of chemical compound that can be applied to the affected area to give relief to Rahul.
(b) Write the name and formula of each of the following:
(i) an acidic salt (ii) a basic salt (iii) a neutral salt.
Ans. (a) Honey bee-sting leaves an acid which causes a great pain and irritation. The use of a base like baking soda on the stung area gives relief to Rahul.
(b) (i) An acidic salt is formed by the reaction between a strong acid and a weak base. Ex -Ammonium chloride NH4Cl.
NH4Cl is formed by the reaction of weak base NH4OH and strong acid HCl.
NH4OH + HCl → NH4Cl + H2O
(ii) A basic salt is formed by the reaction between a strong base and a weak acid. Ex -Sodium acetate - CH3COONa.
CH3COONa is formed by the reaction of strong base sodium hydroxide NaOH and weak acid acetic acid CH3COOH.
CH3COOH + NaOH → CH3COONa + H2O
(iii) A neutral salt is formed by the reaction between a strong acid and a strong base. Ex -Ammonium chloride NaCl.
NaCl is formed by the reaction of strong base NaOH and strong acid HCl.
NaOH + HCl → NaCl + H2O
29. I. A local musician was showing magic in a village street. He took eggshells and poured a solution over it. As a result, if an effervescence were formed. When he took a burning matchstick over it, went off:
(a) Identify the solution poured and a substance present in eggs.
(b) What is the reason behind the effervescence?
(c) Write its balanced chemical equation.
(d) Give the common name of the substance present in eggshell.
Ans. I. (a) The solution poured is acid and a substance present in eggs is calcium carbonate CaCO3.
(b) When an acid reacts with calcium carbonate present in the eggshell to produce carbon dioxide gas which is the reason behind the effervescence.
(c) Chemical reaction is :CaCO3 + H2SO4 → CaSO4 + CO2 + H2O.
(d) Calcium carbonate is resent in eggshell.
30. (a) Acids as well as bases ionized in water. Name the ions produced by each in water.
(b) If we have hydrochloric acid and acetic acid of equal concentration, which will be a strong acid and why?
(c) How will the concentration of hydrogen ion get effected if acid is diluted?
Ans. (a) Acids as well as bases ionized in water. Acid produces hydronium ions in water.
HCl → H+ + Cl-
H+ + H2O → H3O+
(hydronium ions)
(b) Hydrochloric acid is stronger than acetic acid of the same concentration because it completely dissociates into ions but acetic acid does not.
(c) Dilution of acid by mixing water results in a decrease in the concentration of ions (H3O+) per unit volume.
31. (a) Identify the acid and base whose combination forms the common salt that you use in your food. Write the formula and chemical name of this salt. Name the source from where it is obtained.
(b)What is rock salt? Mention its colour and the reason due to which it has this colour.
(c) What happens when electricity is passed through brine? Write the chemical formula for it.
Ans. (a) The acid HCl and the base NaOH whose combination forms the common salt NaCl that we use in your food. The main source of common salt is seawater.
(b) Seawater contains many salts dissolved in it. Sodium chloride is separated from these salts. Deposits of solid salt are also found in several parts of the world. These large crystals are often brown due to impurities. This is called rock salt.
(c) When electricity is passed through an aqueous solution of sodium chloride called brine, it decomposes to form sodium hydroxide.
2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2(g) + H2(g)
Chlorine gas is given off at the anode, and hydrogen gas at the cathode. A sodium hydroxide solution is formed near the cathode.
32. (a) Write the chemical name and chemical formula of washing soda.
(b) How it is obtained from sodium chloride? Give equations of the reaction?
(c) Why is it called a basic salt? Give its anyone uses?
Ans. (a) The chemical name of washing soda is hydrated sodium carbonate and the formula is Na.CO3.10H2O.
(b) NaHCO3 is produced by using sodium chloride as one of the raw materials.
NaCl + H2O + CO2 + NH3 → NH4Cl + NaHCO3
(Sodium chloride) (Ammonium hydrogen carbonate)
When sodium hydrogen carbonate is heated to produce sodium carbonate.
2NaHCO3 + Heat → Na2CO3 + H2O + CO2.
The recrystallization of this sodium carbonate gives washing soda.
Na2CO3 + 10H2O → Na2CO3.10H2O.
33. (a) Name the gas which is liberated when an acid reacts with metal. How will you test the presence of this gas?
(b) Write the chemical equation for the reaction of Zinc metal with.
(i) Hydrochloric acid and (ii) With Sodium hydroxide. Write the chemical name of salt obtained in each case.
(b)Identify the acid and base for Ammonium chloride salt. What would be the nature of the salt? Mention the pH range of the salt.
Ans. (a) Hydrogen gas is liberated when an acid reacts with the metal.
Burning of hydrogen gas with pop sound is the test of hydrogen gas.
(b) (i) Zn metal reacts with HCl to produce ZnCl2 and H2 gas.
Zn + HCl → ZnCl2 + H2
(ii) Zn metal reacts with NaOH to produce sodium zincate NaZnO2 and hydrogen gas. Zn + NaOH → NaZnO2 + H2
(b) Ammonium chloride is formed by the reaction between the strong acid HCl and weak base NH4OH.
Hence ammonium chloride is acidic salt.
pH range of the salt is 4.6 to 6.0.
34. Write a chemical name of Na2CO3.10H2O and Na2CO3. Write the significance of 10H2O. Mention the term used for water molecules attached with a salt. With the help of the chemical equation, explain the method of preparation of both Na2CO3.10H2O and Na2CO3. Also, list two uses of Na2CO3.10H2O.
Ans. Na2CO3.10H2O is washing soda and its chemical name is hydrated sodium carbonate.
Na2CO3 is anhydrous sodium carbonate.
10H2O is the water of crystallisation is the fixed number of water molecules.
When NaHCO3 is heated it gives powder of Na2CO3 and when this powder is recrystallised to get Na2CO3.10H2O that has detergent properties.
NaHCO3 + Heat → Na2CO3 + H2O + CO2
Na2CO3 + 10H2O → Na2CO3.10H2O.
(Sodium carbonate)
Two uses of washing soda (Na2CO3.10H2O) are
i. It is used by doctors as plaster for supporting fractured bones in the right position.
ii. It is used as decorative in buildings.
35. (a) Mention the pH ranges within which our body works. Explain how antacid give relief from acidity? Write the name of one such antacid.
(b) Mention the nature of toothpaste.
Ans. (a) Our body works within the pH range of 7.0 to 7.8.
During indigestion, the stomach produces too much acid and this causes pain and irritation. To get relief from this pain, people use antacids which neutralise the excess acid. Magnesium hydroxide (Milk of magnesia), a mild base is an antacid.
(b) Toothpaste is generally basic. Bacteria present in the mouth produce acids by the degradation of sugar and food particles remaining in the mouth after eating for cleaning the teeth. We use toothpaste that can neutralise excess acid and prevent tooth decay.
36. (a) A metal compound X reacts with dilute H2SO4 to produce effervescence. The gas evolved extinguishes a burning candle. If one of the compound formed is calcium Sulphate, then what are X and the gas evolved? Also, write a balanced chemical equation for the reaction reach which occurred.
(b) Name one antacid. How does it help to relieve indigestion in the stomach
(c) A farmer treats the soil with quick lime or calcium carbonate. What is the nature of soil? Why does the farmer treat the soil with quicklime?
Ans. X is calcium carbonate reacts with sulphuric acid to produce calcium sulphate, carbon dioxide gas, and hydrogen gas.
CaCO3 + H2SO4 → CaSO4 + CO2 + H2.
(b) Magnesium hydroxide (Milk of magnesia), a mild base is an antacid.
During indigestion, the stomach produces too much acid and this causes pain and irritation. To get relief from this pain, people use antacids which neutralize the excess acid.
(c) The soil is acidic so the farmer treats the soil with quick lime or calcium carbonate. Quick lime or calcium carbonate is basic in nature and neutralize the acidic soli.
37. I. Write a balanced chemical equation only for the following chemical properties of acids:
(a) When an acid reacts with metal.
(b) When an acid reacts with metal bicarbonate
(c) When an acid reacts with a base.
II. Three solution A, B, C has pH values 5, 8 and 10 respectively. Among the three which solution has maximum hydrogen ion concentration? Classify the nature of the three solutions as acidic or basic.
Ans. (a) When an acid reacts with the metal to produce salt and hydrogen gas.
HCl + Na → NaCl + H2
(b) When an acid reacts with metal bicarbonate to produce salt, carbon dioxide gas and water.
H2SO4 + 2NaHCO3 → Na2SO4 + 2CO2 + 2H2O.
(c) When an acid reacts with a base to produce salt and water. This reaction is known as neutralisation reaction.
HCl + NaOH → NaCl H2O.
II. pH value of A is 5 which is less than 7 has a maximum value of H+ ions concentration.
pH = 5 means H+ = 10^-5 M/L concentration.
Solution A is acidic as pH value is less than 7 and solutions B and C are basic because they have pH vaue more than 7.
38. (a) Study the following chemical equation. CaSO4.2H2O→CaSO4.1/2H2O +3/2H2O.
Name the reactant and the product and mention one use of the product.
(b) The following salts are formed by the reaction of an acid with a base. Name the acids and base from which these salts are formed. Also mention the nature of the salt, whether it is acidic or basic.
(i) Sodium chloride
(ii) Ammonium nitrate.
Ans. (a) In the reaction, CaSO4.2H2O→CaSO4.1/2H2O +3/2H2O reactant is hydrated calcium sulphate and products are hemihydrate calcium sulphate and water.
(b) (i) Sodium chloride is formed by the reaction of hydrochloric acid with sodium hydroxide.
This salt is formed by the reaction between strong acid and strong base so it is neutral salt.
(ii) Ammonium nitrate is formed by the reaction of nitric acid with ammonium hydroxide. This salt is acidic salt.
This salt is formed by the reaction between strong salt and weak base so it is an acidic salt.
39. Under what soil condition do you think a farmer would treat the soil of these fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?
Ans. Plants require a specific pH range that is 5.5 to 7 for their healthy growth. A farmer would treat the soil of these fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate), when pH value of the soil is lower than 5.5 and soil becomes acidic. Calcium oxide neutralises the acid present in soil.
40. Five solutions A, B, C, D, and E, when tested with universal indicator, showed pH as 4, 1, 11, 7 and 9 respectively. Which solution is it?
(i) Neutral,
(ii) Strongly alkaline,
(iii) Strongly acidic,
(iv) Weakly acidic,
(v) Weakly alkaline.
Arrange the pH in increasing order of hydrogen-ion concentration.
Or
[Do yourself: (a) Explain why is hydrochloric acid a strong acid and acetic weak acid? How can it be verified?
(b) Explain why the aqueous solution of acid conduct electricity.
(c) You have 4 solutions A, B, C, D. The pH of solutions of A is 6, B is 9, C is 12 and D is 7,
(i) Identify the most acidic and most basic solution.
(ii) Arrange the above four solutions in the increasing order of H+ ion concentration.
(iii) State the change in colour of pH paper on dipping in solutions and D.]
Ans. (i) Solution D has pH value 7 hence it is neutral.
(ii) Solution C is strongly alkaline because it has the highest pH value which is more than 7.
(iii) B solution has pH value 1 which is the lowest value and hence it is a strong acid.
(iv) Solution A has pH value is less than 7 and more than B and so it is weakly acidic
(v) E solution has pH 9 that is more than 7 hence it is basic.
