I. Very short answer type questions:
1. What is the skeletal equation?
Ans. The unbalanced chemical equation is a skeletal chemical equation for a reaction.
2. What do you mean by rancidity?
Ans. Rancidity is a chemical process in which fats and oils are oxidized and their smell and taste change.
3. Why it is necessary to balance a chemical equation?
Ans. According to the law of conservation of mass, the number of atoms of each element remains the same, before and after a chemical reaction, so we need to balance a skeletal chemical equation.
4. Define oxidation and reduction.
Ans. If a substance gains oxygen during a reaction, it is said to be oxidized and the reaction is called oxidation reaction. If a substance loses oxygen during a reaction, it is said to be reduced and the reaction is called reduction reaction.
5. Name the gases evolved at anode and cathode on electrolysis of water. What is the ratio of gases?
Ans. Oxygen gas (anion) is evolved at the anode and hydrogen gas (cation) is evolved at the cathode and the ratio of hydrogen to oxygen gas is 2:1.
6. Why do we store silver chloride in dark coloured bottles?
Ans. In the presence of sunlight, decomposition reaction takes place and silver chloride changes into silver and chlorine and turns grey. That is why we store silver chloride in dark coloured bottles.
7. Why is hydrogen peroxide kept in colored bottles?
And. To prevent decomposition reaction hydrogen peroxide kept in colored bottles because in the presence of light hydrogen peroxide decomposes to water and oxygen gas.
8. Why should the magnesium ribbon be cleaned before burning in air?
Ans. A layer of magnesium oxide is formed due to the reaction of magnesium with air on the magnesium ribbon, so the magnesium ribbon should be cleaned before burning in air.
9. What is meant by the endothermic reaction?
Ans. Reactions in which energy is absorbed are known as endothermic reactions.
2AgBr(s) + Sunlight( energy absorbed) → 2Ag(s) + Br2(g)
10. Differentiate between the reaction of magnesium and calcium with water (giving an example).
Ans. Magnesium is less reactive than calcium, Mg reacts with hot water to produce MgO and with an excess of steam, it produces Mg(OH)2 and hydrogen gas whereas calcium reacts with cold water to produce Ca(OH)2.
11. Write the name of brown coloured gas that evolves when lead nitrate crystals are heated in a dry test tube.
Ans. The brown coloured gas is nitrogen dioxide (NO2), that evolves when lead nitrate crystals are heated in a dry test tube.
12. Which one is chemical change - rusting of iron or melting of iron?
Ans. Rusting of iron is a chemical change because in this process a new substance that is iron oxide is formed.
13. Why do silver articles become black after sometimes when exposed to air?
Ans. Silver articles become black after sometimes when exposed to air due to corrosion. In this silver reacts with sulphide present in the air and produces silver sulphide (Ag2S).
14. Give reasons why chips manufacturers usually flush bags of chips with a gas such as nitrogen.
Ans. Chips contain fat and oil and when they are oxidized in air, they become rancid and their smell and taste change, so to prevent rancidity, an oxidant element nitrogen gas which is a very less reactive element and does not react with food is used to flush bags of chips.
15. Write a balanced chemical equation for a chemical combination reaction.
Ans. Chemical combination reaction is a reaction in which two elements combine to produce a compound. Ex - H2 + O2 → H2O
16. What happened when ZnCO3 is heated in the absence of air? Give the relevant equation.
Ans. When ZnCO3 heated in the absence of air it forms ZnO, and CO₂ gas
ZnCO3 → ZnO + CO2
17. Write the chemical equation for reactions that takes place when lead nitrate and potassium iodide solutions are mixed.
Ans. 2Pb(NO3)2(s) + Heat → 2PbO(s) + 4NO2(g) + O2(g)
(Lead nitrate) (Lead oxide) (Nitrogen dioxide) (Oxygen)
18. What happened when quicklime is added to water?
Ans. When quicklime (CaO) is added to water to produce calcium hydroxide and heat.
CaO + H2O → Ca(OH)2 + heat.
19. Name and state the law which is kept in mind while we balance chemical equations.
Ans. The law of conservation of mass that is mass can neither be created nor destroyed in a chemical reaction, therefore the total mass of the elements present in the products has to be equal to the total mass of the elements present in the reactants in a chemical reaction.
20. Give an example of a double displacement reaction.
Ans. Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)
(Sodium sulphate) (Barium chloride) (Barium sulphate) (Sodium chloride)
In this reaction, two reactants exchange ions to form two new compounds which are known as a precipitation reaction.
21. Why decomposition reactions are called the opposite of combination reaction.
Ans. In a decomposition reaction, a compound decomposed to two or more compounds or elements, whereas a combination reaction is a reaction in which two or more elements or compounds combined to form a new single compound, which is the opposite of decomposition reaction.
22. State one basic difference between a physical change and chemical change.
Ans. In physical change no chemical reaction takes place and no new substance is formed but in chemical change a chemical reaction takes place and a new substance is formed.
23. What is meant by a chemical reaction?
Ans. The chemical reaction is a process in which one or more reactants are converted to one or more products by rearranges the constituent atoms of the reactants.
24. Is the burning of a candle wax a physical change or chemical change?
Ans. The burning of candle wax is a chemical change as in this reaction new substances CO2 and H2O are formed.
25. Why respiration considered an exothermic reaction?
Ans. Respiration is a process in which food that is carbohydrates is broken down into simpler substances (digestion) glucose and this glucose combines with oxygen in the cells of our body and gives energy, that is why it is considered as an exothermic reaction.
26. Why photosynthesis is considered an endothermic reaction.
Ans. Photosynthesis is a reaction in which CO2 combines with H2O to form carbohydrates and water by absorbing energy from the sunlight, so it is known as an endothermic reaction.
27. N2 +H2 →2NH3, name the type of reaction and write the balanced chemical equation.
Ans. It is a combination reaction in which N2 combines with H2 to form a new substance NH3.
II. Short answer type questions:
1. Define a chemical reaction. State two observation which helps us to determine that a chemical reaction has taken place. Write one example of each observation with a balanced chemical equation.
Ans. The chemical reaction is a process in which one or more reactants are converted to one or more products by rearranges the constituent atoms of the reactants.
The following observations help us to determine whether
a chemical reaction has taken place – (i) Change in state
Combustion of solid carbon in the presence of oxygen forms gas of CO2.
C(s) + O2(g) = CO2(g)
Combustion of solid carbon in the presence of oxygen forms gas of CO2.
C(s) + O2(g) = CO2(g)
(ii) Change in colour- Reaction between blue coloured copper sulphate and iron gives a green solution of iron sulphate.
CuSO4 + Fe = FeSO4 + Cu
CuSO4 + Fe = FeSO4 + Cu
2. What happens when dilute sulphuric acid is poured on Zinc granules?
Ans. When dilute sulphuric acid poured on zinc granules to form zinc sulphate and hydrogen gas.
Zn + H2SO4 → ZnSO4 + H2.
3. Identify endothermic or exothermic reactions.
(i) Decomposition of ferrous sulphate
(ii) Dissolution of sodium hydroxide in water.
(iii) Dissolution of ammonium chloride in water.
(i) Decomposition of ferrous sulphate
(ii) Dissolution of sodium hydroxide in water.
(iii) Dissolution of ammonium chloride in water.
Ans. (i) The decomposition of ferrous sulphate is an endothermic reaction because in this reaction heat is absorbed.
2FeSO4(s) + Heat → Fe2O3(s) + SO2(g) + SO3(g)
(Ferrous sulphate) (Ferric oxide)
(ii) The dissolution of sodium hydroxide in water is an exothermic reaction because in this reaction heat is evolved.
(iii) The dissolution of ammonium chloride in water is an endothermic reaction because in this reaction heat is absorbed.
4. Silver chloride turns grey when kept in sunlight. Give reason.
Ans. White silver chloride turns grey in sunlight. This is
due to the decomposition of silver chloride into silver and chlorine by
light.
2AgCl(s) Sunlight → 2Ag(s) + Cl2(g).
5. Grapes hanging on the plant do not ferment, but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?
Ans. Grapes hanging on the plant do not ferment due to aerobic respiration as they are alive but after being plucked from the plant can be fermented due to anaerobic respiration as they are not alive.
6. Why do fireflies glow at night?
Ans. Fireflies glow at night because fireflies are bioluminescent insects. They produce a substance by the chemical reaction inside the body that allows them to light up.
7. What is corrosion? Name the compound formed when
(a) Silver corrodes (b) copper corrode.
(a) Silver corrodes (b) copper corrode.
Ans. When a metal is attacked by substances
around it such as moisture, acids, etc., it is said to corrode and this
process is called corrosion.
(a) Silver sulphide is formed after the corrosion of silver.
(b) CuCO3.Cu(OH)2 is formed after the corrosion of copper.
8. When food containing fat or oil is not used and left for a long time they smell and taste changes. Name the process which is responsible for this change. List two methods to prevent or slow down the above change.
Ans. The process is rancidity. When fats and oils are oxidized, they become rancid and their smell and taste change.
Two ways by which rancidity can be prevented are :
i. Keeping food in airtight containers helps to slow down oxidation.
ii. Chips manufacturers usually flush bags of chips with a gas such as nitrogen to prevent the chips from getting oxidised.
9. Write the balanced chemical equations and complete the following reaction and identify the type of reaction.
(i) In thermite reaction, iron III oxide reacts with aluminum.
(ii) Chlorine gas is passed in an aqueous potassium iodide solution.
Ans. (i) In thermite reaction, iron III oxide reacts with aluminum to produce aluminium oxide and heat. This reaction is known as the exothermic reaction.
Fe2O3 + 2Al → Al2O3 + 2Fe Heat.
(ii) Chlorine gas is passed in an aqueous potassium iodide solution to produce potassium chloride solution and solid iodine and this reaction are known as displacement reaction.
2KI + Cl2 → KCl + I2.
10. Identify the type of chemical reaction and also write the chemical equation for the reaction that takes place when a solution of potassium chloride is mixed with silver nitrate solution. Write the chemical name of one of the products obtained.
Ans. When a solution of potassium chloride is mixed with a silver nitrate solution to produce potassium nitrate and silver chloride.
This reaction is known as displacement reaction.
KCl + AgNO3 → KNO3 + AgCl
11. Write balanced chemical equations for the following reactions.
(a) Silver Bromide on exposure to sunlight decomposes into silver and bromine
(b) Sodium metal reacts with water to form sodium hydroxide and hydrogen gas.
Ans. (a) Silver Bromide on exposure to sunlight decomposes into silver and bromine: AgBr(s) + Sunlight → 2AgBr(s) + Br2(g).
(b) Sodium metal reacts with water to form sodium hydroxide and hydrogen gas
: 2Na + 2H2O → 2NaOH + H2.
12. Write balanced chemical equations for the following reactions.
(i) Sodium bicarbonate on reaction with hydrochloric acids.
(ii)Copper sulphate on treatment with potassium iodide.
Ans. (i) Sodium bicarbonate on reaction with hydrochloric acids to produce sodium chloride, carbon dioxide gas and water :
NaHCO3 + HCl → NaCl + CO2 + H2O.
(b) Copper sulphate on treatment with potassium iodide to produce copper iodide and potassium sulphate:
CuSO4 + KI → CuI2 + K2SO4.
13. On heating copper powder in the air, the surface of copper powder becomes coated with black CuO. How can this black coating be converted into brown copper? Write a chemical equation.
Ans. The surface of copper powder becomes coated with black copper(II) oxide. In this reaction, oxygen is added to copper and copper oxide is formed.
2Cu + O2 + heat → 2CuO
If hydrogen gas is passed over this heated material CuO, the black the coating on the surface turns brown as the reverse reaction takes place and copper is obtained. CuO +H2 → Cu + H2O.
14. A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. Write the chemical reaction involved and also mention the type of reaction.
Ans. When a solution of potassium chloride is mixed with a silver nitrate solution to produce white substance potassium nitrate and silver chloride.
This reaction is known as displacement reaction.
KCl + AgNO3 → KNO3 + AgCl
15. A solution of potassium iodide when mixed with lead nitrate solution, an insoluble substance is formed.
(a) Write the balanced chemical reaction involved and also mention the type of reaction.
(b) What is the colour of the precipitate?
(c) Name the compound precipitated.
Ans. (a) A solution of potassium iodide when mixed with lead nitrate solution, an insoluble substance lead iodide and potassium nitrate is formed. This reaction is known as a precipitation reaction.
KI + PbNO3 → KNO3 + PbI
(b) Precipitate potassium iodide is white in colour.
(c) Lead iodide.
16. State the reason, aluminum is more reactive than iron, yet its corrosion is less that of iron.
Ans. Aluminum is more reactive than iron, yet its corrosion is less than iron because when the outer surface of Al comes in contact with the air aluminium make a protective layer of aluminium oxide Al2O3 which is resistive in nature and remain attached to it.
17. Write two observations that you will make when an iron nail is kept in an aqueous solution of copper sulphate. Write the chemical equation for this reaction.
Ans. When an iron nail is kept in an aqueous solution of copper sulphate the iron nail become brownish in colour and the blue colour of copper sulphate solution fade.
The following chemical reaction takes place :
Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
(Iron) (Copper sulphate) (Iron sulphate) (Copper)
18. Write the skeletal equation for the following reactions.
(a) Hydrogen sulphide reacts with Sulpher dioxide to form Sulpher and water
(b) Methane on burning combines with oxygen to produce carbon dioxide and water. What is the need of balance equations?
Ans. (a) Skeletal equation of the reaction -Hydrogen sulphide reacts with Sulpher dioxide to form Sulpher and water.
H2S + SO2 → H2O + S
(b) Skeletal equation of - Methane on burning combines with oxygen to produce carbon dioxide and water:
CH4 + O2 + Heat → CO2 + H2O
According to the law of conservation of mass, the number of atoms of each element remains the same, before and after a chemical reaction. Hence, we need to balance a skeletal chemical equation.
19. Identify the type of chemical reactions from the following equations: Displacement reaction, Combination,
(a) CH4 +2O2 =CO2 +2H2O
(b) CuSO4 + Zn →ZnSO4+ Cu
(c) CaO+H2O→ Ca(OH)2
(d) Pb(NO3)2 +2KI= PbI2 + 2KNO3
Ans. (a)CH4 +2O2 =CO2 +2H2O - oxidation reaction.
(b) CuSO4 + Zn →ZnSO4+ Cu- displacement reaction.
(c) CaO + H2O→ Ca(OH)2 - combination reaction.
(d) Pb(NO3)2 + 2KI= PbI2 + 2KNO3- displacement reaction.
20. When is a chemical reaction categorized precipitation reaction? Explain with two examples.
Ans. The reaction that produces an insoluble substance is called precipitate and the reaction is called a precipitation reaction.
A solution of sodium sulphate, when mixed with barium chloride solution, an insoluble substance barium sulphate, and sodium chloride, is formed.
Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)
(Sodium sulphate)(Barium chloride) (Barium sulphate) (Sodium chloride)
A solution of potassium iodide when mixed with lead nitrate solution, an insoluble substance lead chloride and potassium nitrate are formed.
KI + PbNO3 → KNO3 + PbI.
21. Write a balanced equation for the reaction between magnesium and hydrochloric acid. Name the product obtained, identify the type of reaction
Ans. Magnesium react with hydrochloric acid to produce magnesium chloride and hydrogen gas.
Mg + HCl → MgCl2 + H2
This reaction is displacement reaction.
22. Mention the colour of FeSO4 .7H2O crystals. How does this colour change upon heating? Give balanced chemical equations for the change.
Ans. The colour of FeSO4 .7H2O crystals ight green On heating, ferrous sulphate crystals lose water and anhydrous ferrous sulphate(FeSO4) is formed and the colour changes from light green to white.
FeSO4 .7H2O →FeSO4+ 7H2O
23. What is a combination reaction.? state one example giving a balanced chemical equation for the reaction?
Ans. A reaction in which a single product is formed from two or more reactants is known as a combination reaction.
Ex- Calcium oxide reacts with water to produce single product slaked lime Ca(OH)2 with a large amount of heat.
CaO(s) + H2O(l) → Ca(OH)2
(Quick lime) (Slaked lime)
24. What is redox reaction? Identify the substance oxidized and the substance reduced in the reaction.
(a) PbO+ C →2Pb+ CO.
(b) MnO2 +4HCl→ MnCl2 + 2H2O + Cl2.
Ans. If one reactant gets oxidised while the other gets reduced
during a reaction such reactions are called oxidation-reduction reactions
or redox reactions.
(a) In reaction PbO+ C →2Pb+ CO lead oxide PbO reduced to Pb and C oxidised to CO.
In reaction MnO2 +4HCl→ MnCl2 + 2H2O +Cl2. MnO2 reduced to MnCl2 by removing oxygen and HCl oxidised to Cl2 by removing hydrogen.
25. Barium Chloride reacts with Aluminium Sulphate to give Aluminium Chloride and Barium sulphate.
(a) State the two types in which the above reaction can be classified.
(b)Translate the above statement into a chemical equation.
Ans. (a) Precipitation reaction and double displacement reaction.
(b) Barium Chloride reacts with Aluminium Sulphate to give Aluminium Chloride and Barium sulphate. -
Al2(SO4)3(aq) + 3BaCl2(aq) → 3BaSO4(s) + 2AlCl3(aq)
26. A solution of substance X is used for whitewashing.
(a) Name the substance X and write its formula.
(b) Express the reaction of X with water in the form of a balanced chemical equation.
Ans. (a) Solution of calcium oxide CaO is used for whitewashing. Therefore X is CaO.
(b) Reaction of X (CaO ) with water is : CaO + H2O = Ca(OH)2.
Calcium oxide reacts with water to form calcium hydroxide which is used in whitewashing.
27. (a) list any two changes which take place when oily food gets oxidized.
(b) Mention a measure which prevents or slows down its oxidation.
Ans. (a) When fats and oils are oxidised, they become rancid and their smell and taste change.
(b) Antioxidants that prevent oxidation are added to foods containing fats and oil or keeping food in airtight containers helps to slow down oxidation.
28. Translate the following statements into chemical equations and, then balance it:
(a) Metal in the form of ribbon burns with a dazzling white flame and changes into a white powder.
(b) In a test tube. Hydrochloric acid is poured over a few zinc granules. List two observations that suggest that a chemical reaction has occurred.
Ans. (a) Metal in the form of ribbon burns with a dazzling white flame and changes into a white powder - 2Mg + O2 → 2MgO
(b) In a test tube. Hydrochloric acid is poured over a few zinc granules -
2HCl + Zn → ZnCl2 + H2
Two observations are - i. evolution of hydrogen gas with bubble ii. increase in temperature
29. Convert the following statements into balanced chemical equations:
(a) Zinc reacts with sulphuric acid to form zinc sulphate and hydrogen gas
(b) Magnesium burns in oxygen to form magnesium oxide.
Ans. (a) When zinc reacts with sulphuric acid to form zinc sulphate and hydrogen gas-
Zn + H2SO4 → ZnSO4 + H2
(b) When magnesium burns in oxygen to form magnesium oxide
2Mg + O2 → 2MgO.
30. (a) State the law which is followed in balancing a chemical equation.
(b) Balance the following chemical equation.
Fe + 2H2O→ Fe3O4+ H2
Ans. (a) According to the law of conservation of mass, mass can neither be created nor destroyed in a chemical reaction. That is, the total mass of the elements present in the products be equal to the total mass of the elements present in the reactants.
(b) Balanced chemical equation.
3Fe + 4H2O→ Fe3O4+ 4H2.
31. List 4 observations that help us to determine whether a chemical reaction has taken place:
Ans. Four observations that help us to determine whether a chemical reaction has taken place are:
(a) Evolution of gas
(b) Change in temperature
(c) Change in State
(d) Change in colour.
32. What is meant by a precipitation reaction? Explain by giving an example. Also, give a balanced chemical equation for the reaction stating the states of the reactions and the products formed.
Ans. The reaction that produces an insoluble substance is called a precipitation reaction and insoluble substance is called precipitate.
Ex-
A solution of potassium iodide when mixed with lead nitrate solution, an insoluble substance lead iodide and potassium nitrate are formed.
KI + PbNO3 → KNO3 + PbI.
33. What happens when a piece of
(i) zinc metal is added to copper sulphate solution
(ii) Silver metal is added to copper sulphate solution.
Also write the balanced chemical equation, if a reaction occurs.
Ans. (i) When zinc metal is added to the copper sulphate solution, displacement reaction takes place and to produce zinc sulphate and copper.
Zn + CuSO4 → ZnSO4 + Cu.
(ii) Silver metal is less reactive than copper, therefore the reaction did not take place.
Ag + CuSO4 → No reaction.
III. Long answer type questions:
1. A magnesium ribbon is burnt in oxygen to give a white compound X accompanied by the emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen, it continues to burn and forms a compound Y.(i) Write the chemical formula of X and Y
(ii) Write a balanced chemical equation when X is dissolved in water.
Ans. (i) The chemical formula of X is MgO and Y is Mg3N2.
When a magnesium ribbon is burnt in oxygen to give a white compound MgO accompanied by the emission of light.
Mg + O2 → MgO
and if the burning ribbon is now placed in an atmosphere of nitrogen magnessium nitride is formed.
Mg + N2 → Mg3N2
So The chemical formula of X is MgO and Y is Mg3N2.
(ii) When X (MgO) dissolved in water to produce magnesium hydroxide.
MgO + HO → Mg(OH)2.
2. On heating blue coloured powder of copper II nitrate in a boiling tube, copper oxide(black), oxygen gas and brown gas X are formed.
(i) Write a balanced chemical equation of the reaction.
(ii) Identify the brown gas X evolved.
(iii) Identify the type of reaction.
(iv) What could be the pH range of aqueous solution of the gas X.
Ans. (i) On heating blue coloured powder of copper II nitrate in a boiling tube, copper oxide, oxygen gas, and brown gas are formed
2Cu(NO3)2 + Heat → 2CuO + O2 + 4NO2
(black) (brown)
(ii) Brown gas is NO2 nitrogen dioxide gas.
(iii) This reaction is a thermal decomposition reaction in which on heating Cu(NO3)2 decomposes to CuO, O2 and NO2.
(iv) Aqueous solution gas X means NO2 is acidic because it is a nonmetallic oxide and its pH value would be between 1 to 7.
3. Write the balanced chemical equations for the following reaction and identify the type of reaction.
(i) Sodium hydroxide solution is treated with acetic acid.
(ii) Ethanol is warmed with ethanoic acid in the presence of sulphuric acid.
(iii) Ethane is burnt in the presence of oxygen.
(i) Sodium hydroxide solution is treated with acetic acid.
(ii) Ethanol is warmed with ethanoic acid in the presence of sulphuric acid.
(iii) Ethane is burnt in the presence of oxygen.
Ans. (i) When sodium hydroxide reacts with acetic acid it forms sodium acetate and water. NaOH + CH3COOH → CH3COONa + H2O.
It is a neutralization reaction.
(ii) When ethanol is warmed with ethanoic acid in the presence of sulphuric acid it produces ethyl acetate and water.
C2H5OH + CH3COOH → CH3COOC2H5 + H2O.
This reaction is known as an esterification reaction.
(iii) When ethane is burnt in the presence of oxygen it forms CO2, water, heat, and light. This reaction is known as the combustion reaction.
C2H6+ O2 → CO2 + H2O + Heat + Light.
It is a neutralization reaction.
(ii) When ethanol is warmed with ethanoic acid in the presence of sulphuric acid it produces ethyl acetate and water.
C2H5OH + CH3COOH → CH3COOC2H5 + H2O.
This reaction is known as an esterification reaction.
(iii) When ethane is burnt in the presence of oxygen it forms CO2, water, heat, and light. This reaction is known as the combustion reaction.
C2H6+ O2 → CO2 + H2O + Heat + Light.
4. Identify endothermic or exothermic reactions.
(i) CH4 +2O2 → CO2 + H2O
(ii) CaO+ H2O → Ca(OH)2 .
(iii) Dilution of an acid
(iv) Evaporation of water
(v) Sublimation of camphor.
Ans. (i) CH4 +2O2 → CO2 + H2O - the reaction is an exothermic reaction.
(ii) CaO+ H2O → Ca(OH)2 - the reaction is an exothermic reaction.
(iii) Dilution of acid - the reaction is an exothermic reaction.
(iv) Evaporation of water- the reaction is an endothermic reaction.
(v) Sublimation of camphor- the reaction is an endothermic reaction.
5. Give the characteristics test for the following gases
(i) CO2 (ii) SO2 (iii)O2 (iv) H2.
Ans. (i) Carbon Dioxide gas CO2 is acidic in nature, it changes the colour of blue litmus to red or when CO2 gas is passed through lime water it turns milky.
(ii) Sulphur dioxide is an odorless and pungent gas.
Sulphur dioxide gas turns acidified potassium dichromate solution from orange to green colour.
(iii) O2 gas is a good supporter of Combustion. So if a burning match stick is brought near the gas it burns more vigorously.
(iv) When a burning match stick is brought near Hydrogen gas, the match stick burns with a pop sound.
6. What happens when zinc granules are treated with a dilute solution of H2SO4, HCL, HNO3 NaCl and NaOH, also write the chemical
equations, if a reaction occurs?
Ans. When zinc granules react with :
i. a dilute solution of H2SO4 to produces zinc sulphate and hydrogen gas.
H2SO4 + Zn → ZnSO4 + H2.
ii. a dilute solution of HCl produces zinc chloride and hydrogen gas.
HCl + Zn → ZnCl2 + H2.
iii. a dilute solution of HNO3 to produces zinc nitrate and hydrogen gas.
HNO3 + Zn → ZnNO3 + H2.
iv. Zn is less reactive than sodium, therefore the reaction did not take place.
NaCl + Zn → No reaction.
v. a dilute solution of NaOH to produces sodium zincate and hydrogen gas.
2NaOH + Zn → Na2ZnO2 + H2.
7. On adding a drop of Barium Chloride solution to an aqueous solution of sodium sulphate, a white precipitate is obtained.
(i) Write a balanced chemical equation of the reaction involved
(ii) What another name can be given to this precipitation reaction?
(iii) On adding dilute hydrochloric acid to the reaction mixture, white precipitate disappears. Why?
Ans. (i)When a drop of Barium Chloride solution added to an aqueous solution of sodium sulphate, a white precipitate of barium sulphate and sodium chloride are obtained -
BaCl2 + Na2SO4 → BaSO4 + 2NaCl
(ii) Another name of this precipitation reaction is a double displacement reaction.
(iii) On adding dilute hydrochloric acid to the reaction mixture, Barium Chloride, Sulphur dioxide, and water are formed. Barium chloride is a soluble substance so white precipitate disappears.
BaSO3 + HCl → BaCl3 + SO2 + H2O.
8. Give reasons for the following:
During the reaction of some metals with dilute hydrochloric acid, the following observations were made:
(i) Silver metal does not show any change.
(ii) The temperature of the reaction mixture rises when aluminium (Al) is added.
(iii) The reaction of sodium metal is found to be highly explosive.
(iv) Some bubbles of gas are seen, when lead (Pb) is reacted with the acid.
(v) A gas is produced when sodium carbonate is added to the acid.
Ans. (i) Silver metal does not show any change because it is a very less reactive metal.
(ii) The temperature of the reaction mixtures rises when Aluminium is added because it is an exothermic reaction.
(iii) The reaction of sodium metal is found to be highly explosive because sodium is a very highly reactive metal and large amount of heat is produced in the reaction. It is an exothermic thermic reaction.
(iv) Some bubbles of gas are seen, when lead (Pb) is reacted with the acid because in this reaction hydrogen gas is formed.
(v) Sodium carbonate reacts with HCl to produce sodium chloride and carbon dioxide gas.
9. Write balanced chemical equations for the following reactions:
(a) Dilute sulphuric acid reacts with Aluminium powder.
(b) Dilute hydrochloric acid reacts with sodium carbonate.
(c) Carbon dioxide is passed through lime water.
Ans. (a) Dilute sulphuric acid when reacts with aluminium powder to produces aluminium sulphate and hydrogen gas.
2Al + 3H2SO4 → Al2(SO4)3+ 3H2
(b) Dilute hydrochloric acid when reacts with sodium carbonate to produces sodium chloride, carbon dioxide gas, and water.
Na2CO2 + 2HCl → 2NaCl + CO2 + H2O.
(c) When carbon dioxide gas is passed through lime water, insoluble calcium carbonate and water are formed and lime water turns into milky.
2Ca(OH)2 + 2CO2 → 2CaCO3 + 2H2O.
10. (a) Give an example for a combination reaction which is exothermic
(b) Identity oxidizing agent in the following reaction.
H2S+Cl2 → 2HCl + S
(c) Name the phenomenon due to which the taste and smell of oil change when kept for a long time in open. Suggest one method to prevent it.
Ans. (a) Reactions in which heat is released along with the formation of products are called exothermic chemical reactions.
Example of an exothermic reaction is –
C + O2 → CO2 + Heat.
(b) The oxidizing agent in the reaction H2S+Cl2 → 2HCl + S is chlorine Cl2
by being reduced and gaining hydrogen atoms.
(c) The phenomenon is rancidity due to which the taste and smell of oil change when kept for a long time in open. The method to prevent it is adding of antioxidants, keeping food in an airtight container or flush bags of foods containing fats and oil with a gas such as nitrogen.
11. I. What is rancidity? Mention any two ways by which rancidity can be prevented.
II. Write balanced chemical equations for the reactions that take place during respiration. Identify the type of combination reaction that takes place during this process and justifies the name. Give one more example of this type of reaction.
Ans. I. When fats and oils are oxidized, they become rancid and their smell and taste change, this process is known as rancidity.
Two ways by which rancidity can be prevented are :
a. Keeping food in airtight containers helps to slow down oxidation.
b. Chips manufacturers usually flush bags of chips with a gas such as nitrogen to prevent the chips from getting oxidised.
II. The balanced chemical equations for the reactions that take place during respiration:
C6H12O6(aq) + 6O2(aq) → 6CO2(aq) + 6H2O(l) + energy
(Glucose)
During digestion, food that contains carbohydrates is broken down into simpler substances glucose. This glucose combines with oxygen in the cells of our body and provides energy. The special name of this reaction is respiration.
This reaction is known as the exothermic reaction.
The decomposition of vegetable matter into compost is also another example of an exothermic reaction.
12. In the electrolysis of water
(a) Name the gas collected at the cathode and anode respectively.
(b) Why is the volume of one gas collected at one electrode double that at the other? Name this gas.
(c) How will you test the evolved gases?
Ans. (a) In the process of electrolysis of water, hydrogen gas collected at cathode and oxygen gas is collected at the anode.
(b) According to molecular formula of water H2O, two atoms of hydrogen and one atom of oxygen are present in one molecule of water. Therefore hydrogen gas collected at cathode double that at the anode in which oxygen gas collected.
(c) If a burning match stick is brought near the oxygen gas it burns more vigorously.
(iv) When a burning match stick is brought near Hydrogen gas, the match stick burns with a pop sound.
13. Name the salts that are used in black and white photography. Give reactions when they are exposed to light. Define the type of chemical reactions taking place.
Ans. Silver chloride and silver bromide are salts used in black and white photography.
White silver chloride turns grey in sunlight due to the decomposition of silver chloride into silver and chlorine by light.
2AgCl(s) + Sunlight → 2Ag(s) + Cl2(g)
Silver bromide also behaves in the same way.
2AgBr(s) + Sunlight → 2Ag(s) + Br2(g)
A decomposition reaction takes place.
A decomposition reaction is a reaction in which a single reactant breaks down to give simpler products.
14. I. A small amount of calcium oxide is taken in a beaker and water is added slowly to it
(a) Will there be any change in temperature of the contents? Explain.
(b) Name and define what type of reaction taking place.
(c) Write chemical equations for the above reaction.
II. A substance X which is an oxide of a group 2 element, 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 chemical reactions involved.
Ans.
I. (a) When a small amount of calcium oxide is taken in a beaker and water is added slowly to it there will be an increase in temperature of the contents.
(b) It is an exothermic reaction, in this reaction a large amount of heat is evolved.
(c) When calcium oxide reacts with water to form calcium hydroxide and heat.
CaO + H2O → Ca(OH)2 + Heat
II. Substance X is calcium oxide used in the cement industry and it present in bones.
When CaO reacts with water to form calcium hydroxide and large amount of heat. The solution calcium hydroxide which is chemically basic in nature turns red litmus blue.
CaO + H2O → Ca(OH)2 + Heat.
15. 2g of ferrous sulphate crystals are heated in a boiling tube.
(a) State the colour of ferrous sulphate crystal both before heating and after heating.
(b) Name the gases produced during heating
(c) Write the chemical equation for the reaction.
Ans. The colour of ferrous sulphate crystal is green before heating and after heating, ferrous sulphate crystals lose water and anhydrous ferrous sulphate is formed so colour changes from green to white. On further heating ferrous sulphate decompose to ferric oxide and colour changes to brown.
(b) sulphur dioxide (SO2) and sulphur trioxide (SO3) gases are formed during heating.
(c) The chemical reaction is :
2FeSO4(s) → Heat Fe2O3(s) + SO2(g) + SO3(g)
(Ferrous (Ferric oxide)
sulphate)
16. Describe an activity to show a decomposition reaction in which light is used to decompose reactants. Write the chemical equation of the reaction and state its one use.
Ans. An activity to show a decomposition reaction in which light is used to decomposition reaction:
Take about 2 g silver chloride in a china dish which is white in colour. Place this china dish in sunlight for some time. After some time we will see that white silver chloride turns grey in sunlight. This is due to the decomposition of silver chloride into silver and chlorine by light.
2AgCl(s) + Sunlight→ 2Ag(s) + Cl2(g)
Silver bromide also behaves in the same way.
2AgBr(s) + Sunlight → 2Ag(s) + Br2(g)
The above reactions are used in black and white photography
17. Give reasons for the following:
(a) All decomposition reactions are endothermic reactions.
(b) Color of copper sulphate solution change when an iron nail is dipped in it.
(c) Respiration is an exothermic reaction.
Ans. (a) The decomposition reactions require energy either in the form of heat, light or electricity for breaking down the reactants and the reactions in which energy is absorbed are known as endothermic reactions.
(b) Color of copper sulphate solution change when an iron nail is dipped in it because in this displacement reaction the blue coloured copper sulphate displaced by iron to form green colour ferrous sulphate crystals.
(c) In the process of respiration, during digestion, carbohydrates of food are broken down into simpler substances glucose and this glucose combines with oxygen in the cells of our body and provides energy. So this reaction is known as an exothermic reaction.
C6H12O6(aq) + 6O2(aq) → 6CO2(aq) + 6H2O(l) + energy
(Glucose)
18. A brown substance X on heating in the air forms a substance Y. When hydrogen gas is passed over heated Y it again changes back into X. (a) name the substances X and Y.
(b) name the chemical process of occurring during both the changes.
(c) Write the chemical equations involved in both the changes.
Ans. The brown substance is copper which on heating in the air forms a substance copper oxide. When hydrogen gas is passed over heated copper oxide again changes back into copper Cu.
(a) The name the substances X is Copper and Y Is Copper oxide.
(b) In the first case reaction is oxidation reaction and in the second case reaction is a reduction reaction.
(c) Chemical equation: When copper is heated in the air forms a substance copper oxide.
CuO + H2 ➝ Cu + H2O
When hydrogen gas is passed over heated copper oxide again changes back into copper cu.
CuO + H2 ➝ Cu + H2O
19. 2g of Lead Nitrate powder is taken in a boiling tube. The boiling tube is heated over the flame. Now answer the following:
(a) State the colour of the fumes evolved and the residue left.
(b) Name the type of chemical reaction that has taken place stating its balanced equation.
Ans. (a ) The color of the fumes is brown and the colour of the residue left is white.
(b) It is the decomposition reaction. In this reaction, a single reactant lead nitrate breaks down to give simpler products lead oxide, nitrogen dioxide, and nitrogen try oxide.
When 2g of Lead Nitrate is heated lead oxide, brown fumes of NO2 is formed.
The balanced equation is:
2Pb(NO3)2 ➝ 2PbO + 4NO2 +O2
(Lead nitrate) (Lead (Nitrogen (Oxygen)
Oxide) dioxide)
20. When a chemical reaction considered a double displacement reaction? Explain by giving an example.
State a difference between displacement and double displacement reaction.
Ans. A double displacement reaction is a type of reaction where two reactants exchange ions to form two new compounds. Double displacement reactions typically result in the formation of a product that is a precipitate.
Example:
The reaction between silver nitrate and sodium chloride is a double displacement reaction.
AgNO3 + NaCl → AgCl + NaNO3
The main difference between displacement and double displacement reaction is that in a displacement reaction, a single element is replaced from a compound by another more reactive element whereas, in double displacement reaction, two elements are displaced.
21. (a) What is an oxidation and reduction reaction? Identify in the following reaction, the substance oxidised and the substance reduced.
ZnO + C = Zn + CO.
(b) State the meaning of oxidation in a chemical reaction. Consider the chemical reaction represent by the following equation and write the name of the substance oxidized or reduced, oxidizing agent and reducing agent in the reaction. MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
Ans. (a) The reaction in which oxygen is added or hydrogen is removed from a compound is called oxidation reaction and the reaction in which hydrogen is added or oxygen is removed from a substance is called reduction reaction.
In the reaction : ZnO + C = Zn + CO
Carbon is oxidised to CO by the addition of oxygen and ZnO is reduced to Zn
by the removal of oxygen.
(b) The reaction in which oxygen is added or hydrogen is removed from a compound is called oxidation reaction. The meaning of oxidation in a chemical reaction is losing of electrons during the reaction to get stability.
In the reaction MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
MnO2 is reduced to MnCl2 and HCl is oxidised to chlorine.
22. Differentiate between a combination reaction and a decomposition reaction. Write one chemical equation each for this reaction.
Ans. A combination reaction is a reaction in which a single product is formed from two or more reactants is known as a combination reaction whereas decomposition reaction is a reaction in which a single reactant breaks down to give simpler products.
Example for combination reaction:
Calcium oxide reacts vigorously with water to produce calcium hydroxide and releases a large amount of heat.
CaO(s) + H2O(l) → Ca(OH)2
(Quick lime) (Slaked lime)
Example of a decomposition reaction:
By the heating of calcium carbonate, it decomposes into calcium oxide and carbon dioxide.
CaCO3 → CaO + CO2 23. The student takes 2 gm of ferrous sulphate crystal in a dry test tube and heat the test tube. Answer the following questions on the basis of observations made by the student:
(a) Write an observation about colour of residue or smell of gas evolved.
(b) Name the type of chemical reaction (c) Write a balanced chemical equation for the reaction involved.
Ans. (a) The colour of FeSO4 .7H2O crystals light green. On heating, ferrous sulphate crystals lose water and anhydrous ferrous sulphate(FeSO4) is formed and the colour changes from light green to white. On further heating ferrous sulphate decompose to ferric oxide and colour changes to brown.
Brown reddish solid left behind is a ferric oxide (Fe2O3).
The smell of burning sulphur is due to SO2 & SO3 gases.
(b) Type of reaction is a decomposition reaction in which ferrous sulphate decomposes to ferric oxide, sulphur dioxide and sulphur trioxide.
(c) The chemical reaction is :
2FeSO4(s) → Heat Fe2O3(s) + SO2(g) + SO3(g)
(Ferrous (Ferric oxide)
sulphate)
24. Differentiate between an exothermic reaction and an endothermic reaction. Write one example for each one of these reactions in the form
of a balanced chemical equation.
In the reaction MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
MnO2 is reduced to MnCl2 and HCl is oxidised to chlorine.
22. Differentiate between a combination reaction and a decomposition reaction. Write one chemical equation each for this reaction.
Ans. A combination reaction is a reaction in which a single product is formed from two or more reactants is known as a combination reaction whereas decomposition reaction is a reaction in which a single reactant breaks down to give simpler products.
Example for combination reaction:
Calcium oxide reacts vigorously with water to produce calcium hydroxide and releases a large amount of heat.
CaO(s) + H2O(l) → Ca(OH)2
(Quick lime) (Slaked lime)
Example of a decomposition reaction:
By the heating of calcium carbonate, it decomposes into calcium oxide and carbon dioxide.
CaCO3 → CaO + CO2 23. The student takes 2 gm of ferrous sulphate crystal in a dry test tube and heat the test tube. Answer the following questions on the basis of observations made by the student:
(a) Write an observation about colour of residue or smell of gas evolved.
(b) Name the type of chemical reaction (c) Write a balanced chemical equation for the reaction involved.
Ans. (a) The colour of FeSO4 .7H2O crystals light green. On heating, ferrous sulphate crystals lose water and anhydrous ferrous sulphate(FeSO4) is formed and the colour changes from light green to white. On further heating ferrous sulphate decompose to ferric oxide and colour changes to brown.
Brown reddish solid left behind is a ferric oxide (Fe2O3).
The smell of burning sulphur is due to SO2 & SO3 gases.
(b) Type of reaction is a decomposition reaction in which ferrous sulphate decomposes to ferric oxide, sulphur dioxide and sulphur trioxide.
(c) The chemical reaction is :
2FeSO4(s) → Heat Fe2O3(s) + SO2(g) + SO3(g)
(Ferrous (Ferric oxide)
sulphate)
24. Differentiate between an exothermic reaction and an endothermic reaction. Write one example for each one of these reactions in the form
of a balanced chemical equation.
Examples of exothermic reactions are:
Burning of natural gas: CH4(g) + 2O2 (g) → CO2 (g) + 2H2O (g)
Reactions in which energy is absorbed are known as endothermic reactions.
Example of endothermic reaction:
The decomposition of silver chloride into silver and chlorine by light.
2AgCl(s) + Sunlight energy → 2Ag(s) + Cl2(g)
25. A combination reaction is the reverse of a decomposition reaction. Justify this statement with the help of appropriate chemical equations of each.
Ans. A combination reaction is a reaction in which a single product is formed from two or more reactants is known as a combination reaction whereas decomposition reaction is a reaction in which a single reactant breaks down to give two or more products. So A combination reaction is the reverse of a decomposition reaction.
A + B = AB Combination reaction
AB → A + B Decomposition reaction.
Example for combination reaction:
Hydrogen gas reacts with oxygen to form water: H2 + O2 → H2O
Example of a decomposition reaction: 2H2O → 2H2 + O2
26. In the following. Chemical reaction zinc oxide reacts with carbon to produce Zinc metal and carbon monoxide. ZnO + C → Zn + CO
(a) Identify the substance getting oxidized and getting reduced.
(b) State the reason for choosing the substances in (a).
(c) Name the type of reaction and give another example of a similar type of reaction.
Ans. (a) In the reaction ZnO + C → Zn + CO
Carbon is oxidised to CO and ZnO is reduced to Zn.
(b) The carbon is gaining oxygen and is being oxidised. During this reaction, the ZnO is losing oxygen and is being reduced.
(c) One reactant gets oxidised while the other gets reduced during a reaction. Such a reaction is called oxidation-reduction reactions or redox reactions.
Another example is:
When copper is heated in the air forms a substance copper oxide. In this reaction, CuO is losing oxygen and is being reduced and the hydrogen is gaining oxygen and is being oxidised.
CuO + H2 ➝ Cu + H2O .
27. A decomposition reaction required energy in the form of heat or electricity. Give one example of each.
Ans. When a decomposition reaction is carried out by heating, it is called thermal decomposition. Decomposition of calcium carbonate to calcium oxide and carbon dioxide on heating is an example of a thermal decomposition reaction.
Example: CaCO3(s) → Heat CaO(s) + CO2(g)
(Limestone) (Quick lime)
When a decomposition reaction is carried out by electricity, it is called electrolysis. The decomposition of water to hydrogen and oxygen on passing electricity through acidified water an example of electrolysis of water.
Example: H2O(l) → H2(g) + O2(g)
(Water) (Hydrogen) (Oxygen)
28. I. Aqueous solution of sodium sulphate and barium Chloride reacts as follows :ZnSO4 +BaCl2→ BaSO4 + 2NaCl.
(a) Identify the type of reaction
(b) Define the type of reaction
(c) Suggest another name for this reaction.
II. Define the following terms:
(i) Corrosion (ii)Rancidity. Give one example of each
Ans. I. (a) The reaction is a double displacement reaction.
(b) The double displacement reaction is the reaction in which there is an exchange of ions between the reactants.
(c) Another name of this reaction is the precipitation reaction.
II. (a) When a metal is attacked by substances around it such as moisture, acids, etc., it is said to corrode and this process is called corrosion.
An example is: Silver sulphide is formed after the corrosion of silver.
(b) Rancidity is a chemical process in which fats and oils are oxidised and their smell and taste change.Example: When fats and oils are oxidised, they become rancid and their smell and taste change.
29. (a) Most of the metals acquired a dull surface when exposed to air. Name the chemical phenomenon responsible for this process.
(b) State the conditions under which the iron articles get rust. Design an activity to investigate the conditions necessary for rusting. Suggest any two methods to prevent rusting of iron.
Ans. (a) Most of the metals acquired a dull surface when exposed to air and this chemical phenomenon is known as corrosion.
(b) In the presence of water and oxygen, iron articles get rust.
Activity - We can use 3 test-tube,
put only air and iron in 1, water and oil to stop air in 2 with iron and in 3 water, air, iron.
Only in 3, it will get rusted
The two methods to prevent rusting are-
a) Painting the surface of iron articles.
b) Galvanization with zinc over the iron articles.
30. I. Accounts for the following:
(a) Paint is applied to the Iron article
(b) Oil and fat containing food items are flushed with nitrogen.
(c) When Iron nails kept in copper sulphate solution, the blue colour of the solution fades and Iron nails become brownish.
II. Account for the following:
(a) White silver chloride turns grey in sunlight.
(b) Brown colored copper powder on heating in the air turns into a black-colored substance.
Ans. I (a) Paint is applied to the iron article to protect from rusting of iron or corrosion.
(b) Oil and fat containing food items are flushed with nitrogen because nitrogen doesn't react with the food products and prevents rancidity.
(c) When Iron nails kept in blue coloured copper sulphate solution, the blue colour of the solution fades due to the formation of iron sulphate.
II. (a) White silver chloride turns grey in sunlight. This is due to the decomposition of silver chloride into silver and chlorine in the presence of light.
31. What do you mean by?
(a) Displacement reaction
(b) Reduction reaction.
(c) Oxidation reaction.
(d) Decomposition reaction.
(e) Combination reaction?
Explain with suitable example.
Ans. (a) Displacement reaction is a reaction in which a single element is replaced from a compound by another more reactive element.
Example: Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)
(Copper sulphate) (Zinc sulphate)
Zinc is more reactive elements than copper. Zn displaces copper from its compound copper sulphate.
(b) The reduction reaction is a reaction in which a substance loses oxygen during a reaction and substance is said to be reduced.
Example: CuO +H2 → Cu + H2O
During this reaction, the copper(II) oxide is losing oxygen and is being reduced.
(c) If a substance gains oxygen during a reaction, it is said to be oxidised and reaction is known as an oxidation reaction.
Example: Oxygen is added to copper and copper oxidised to copper oxide.
2Cu + O2 + Heat → 2CuO.
(d) Decomposition reaction a reaction in which a single reactant breaks down to give simpler products.
Example: Decomposition of calcium carbonate to calcium oxide and carbon dioxide on heating
CaCO3(s) + Heat → CaO(s) + CO2(g)
(Limestone) (Quick lime)
(e) A reaction in which a single product is formed from two or more reactants is known as a combination reaction.
Example: Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat.
CaO(s) + H2O(l) → Ca(OH)2(aq)
(Quick lime) (Slaked lime)
32. I. Solid calcium oxide was taken in a container and water was added slowly to it.
(a) Write the observation,
(b) Write the chemical formula of the product formed.
II. What happens when carbon dioxide gas is bubbled through lime water?
(a) In a small amount
(b) In excess?
Ans. I. (a) Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat.
(b) CaO(s) + H2O(l) → Ca(OH)2(aq)
(Quick lime) (Slaked lime)
In this reaction, calcium oxide and water combine to form a single product, calcium hydroxide, and this reaction is known as a combination reaction.
II. (a) When carbon dioxide gas is bubbled through lime water in a small amount, lime water turns into milky due to the formation of insoluble calcium carbonate.
Reaction : Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)
(b) In excess, milkiness of solution of the solution of lime water disappears due to the formation of calcium bicarbonate.
Reaction:
CO2+H2O→ H2CO3
CaCO3 + H2CO3 → Ca(HCO3)2
33. I. (a) Why do you apply Paint on Iron articles?
(b)What happens chemically when quicklime is added to water.
(c) Balance the following chemical equation. MnO2 +HCl→MnCl2+Cl2+H2O.
II. Give one example each of a chemical reaction described by:
(a) evolution of gas
(b) change in colour
(c) formation of precipitate
(d) change in temperature.
(e) change in state.
Ans. I. (a) Paint is applied to the iron article to protect from rusting of iron or corrosion.
(b) When quicklime (CaO) is added to water to produce calcium hydroxide and heat.
CaO + H2O → Ca(OH)2 + heat.
(c) Balancing of chemical equation :MnO2 +HCl→MnCl2+Cl2+H2O is as follows:
MnO2 + 4HCl→MnCl2 + Cl2+ 2H2O.
II. (a) Evolution of gas - Reaction between copper and dilute sulphuric acid.
Forms copper sulphate and hydrogen gas.
b) Change in color - Reaction between blue coloured copper sulphate and iron gives a green solution of iron sulphate.
c) Formation of a precipitate - Reaction between potassium iodide and lead nitrate forms a yellow precipitate of lead iodide.
d) Change in temperature - Reaction between calcium oxide and water.
e) Change in state - Combustion of solid carbon in the presence of oxygen forms gas of CO2.
34.Balance the following equations :
(i) Hg(NO3)2 ⎯⎯⎯→Hg + NO2 + O2 heat.
(ii) NaNO3 ⎯⎯⎯→NaNO2 + O2 he
(iii) Ca + H2O ⎯⎯→ Ca(OH)2 + Heat
(iv) NaNO3 + H2SO4→ Na2SO4+ HNO3
(v) Na2CO3 + H2O + CO2 ⎯⎯→ NaHCO3
(vi) Mg + HCl ⎯⎯→ MgCl2 + H2
(vii) Na +H2O ⎯⎯→ NaOH + H2
(viii) C4H10 + O2⎯⎯→ CO2 + H2O
(ix) FeS + HCl ⎯⎯→ FeCl2 + H2S
(x) MnO2 + HCl ⎯⎯→MnCl2+H2O + Cl2
(xi) Mg3N2 + H2O ⎯⎯→ Mg(OH)2 + NH3
(xii) NH3 + O2 → N2 + H2O
(xiii) MgCl2 + Na2CO3 →NaCl+ MgCO3
(xiv) NaOH + → NaCl + NaClO + H2O
(xv) FeCl3 + NaOH → NaCl + Fe(OH)3
(xvi) NaCl + MnO2 +H2SO4→NaHSO4+ MnSO4 + H2O + Cl2
(xvii) KNO3 + H2SO4→ K2SO4 + HNO3
(xviii) PbO + HNO3 → Pb(NO3)2 +H2O
(xix) FeSO4 + NaOH → Na2SO4+ Fe(OH)2
(xx) Fe2(CO2)3 + H2SO4 →Fe2(SO4)3 + CO2 + H2O
(xxi) Ca(OH)2 + HNO3 ⎯→ Ca(NO3)2 + H2O
(xxii) BaCl2 + H2SO4 → BaSO4 + HCl
(xxiii) H2SO4 + NaOH → Na2SO4+ H2O
(xxviii) Pb(NO3)2 → PbO + NO2 + O2
(xxix) KClO3 → KCl + O2
(iv) 2NaNO3 + H2SO4→ Na2SO4+ 2HNO3
(v) Na2CO3 + H2O + CO2 ⎯⎯→ 2NaHCO3
(vi) Mg + 2HCl ⎯⎯→ MgCl2 + H2
(vii) 2Na + 2H2O ⎯⎯→ 2NaOH + H2
(viii) 2C4H10 + 13O2⎯⎯→ 8CO2 + 10H2O
(ix) FeS + 2HCl ⎯⎯→ FeCl2 + H2S
(x) MnO2 + 2HCl ⎯⎯→MnCl2+H2O + Cl2
(xi) Mg3N2 + 6H2O ⎯⎯→ 3Mg(OH)2 + 2NH3
(xii) 4NH3 + 3O2 → 2N2 + 6H2O
(xiii) MgCl2 + Na2CO3 → 2NaCl + MgCO3
(xiv) 2NaOH + Cl → NaCl + NaClO + H2O
(xv) FeCl3 + 3NaOH → 3NaCl + Fe(OH)3
(xvi) 2NaCl + MnO2 + 2H2SO4→ Na2SO4+ MnSO4 + 2H2O + Cl2
(xvii) 2KNO3 + H2SO4→ K2SO4 + 2HNO3
(xviii) PbO + 2HNO3 → Pb(NO3)2 +H2O
(xix) FeSO4 + 2NaOH → Na2SO4+ Fe(OH)2
(xx) Fe2(CO3)3 + 3H2SO4 →Fe2(SO4)3 + 3CO2 + 3H2O
(xxi) Ca(OH)2 + 2HNO3 ⎯→ Ca(NO3)2 + 2H2O
(xxii) BaCl2 + H2SO4 → BaSO4 + 2HCl
(xxiii) H2SO4 + 2NaOH → Na2SO4+ 2H2O
(xxviii) Pb(NO3)2 → PbO + 2NO2 + O2
(xxix) 2KClO3 → 2KCl + 3O2
Ans. (a) Most of the metals acquired a dull surface when exposed to air and this chemical phenomenon is known as corrosion.
(b) In the presence of water and oxygen, iron articles get rust.
Activity - We can use 3 test-tube,
put only air and iron in 1, water and oil to stop air in 2 with iron and in 3 water, air, iron.
Only in 3, it will get rusted
The two methods to prevent rusting are-
a) Painting the surface of iron articles.
b) Galvanization with zinc over the iron articles.
30. I. Accounts for the following:
(a) Paint is applied to the Iron article
(b) Oil and fat containing food items are flushed with nitrogen.
(c) When Iron nails kept in copper sulphate solution, the blue colour of the solution fades and Iron nails become brownish.
II. Account for the following:
(a) White silver chloride turns grey in sunlight.
(b) Brown colored copper powder on heating in the air turns into a black-colored substance.
Ans. I (a) Paint is applied to the iron article to protect from rusting of iron or corrosion.
(b) Oil and fat containing food items are flushed with nitrogen because nitrogen doesn't react with the food products and prevents rancidity.
(c) When Iron nails kept in blue coloured copper sulphate solution, the blue colour of the solution fades due to the formation of iron sulphate.
II. (a) White silver chloride turns grey in sunlight. This is due to the decomposition of silver chloride into silver and chlorine in the presence of light.
2AgCl(s) Sunlight → 2Ag(s) + Cl2(g).
(b) Brown colored copper powder on heating in the air turns into a black colored substance. This is due to the combination reaction of copper and oxygen to form black copper oxide.
2Cu + O2 → 2CuO.
(b) Brown colored copper powder on heating in the air turns into a black colored substance. This is due to the combination reaction of copper and oxygen to form black copper oxide.
2Cu + O2 → 2CuO.
31. What do you mean by?
(a) Displacement reaction
(b) Reduction reaction.
(c) Oxidation reaction.
(d) Decomposition reaction.
(e) Combination reaction?
Explain with suitable example.
Ans. (a) Displacement reaction is a reaction in which a single element is replaced from a compound by another more reactive element.
Example: Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)
(Copper sulphate) (Zinc sulphate)
Zinc is more reactive elements than copper. Zn displaces copper from its compound copper sulphate.
(b) The reduction reaction is a reaction in which a substance loses oxygen during a reaction and substance is said to be reduced.
Example: CuO +H2 → Cu + H2O
During this reaction, the copper(II) oxide is losing oxygen and is being reduced.
(c) If a substance gains oxygen during a reaction, it is said to be oxidised and reaction is known as an oxidation reaction.
Example: Oxygen is added to copper and copper oxidised to copper oxide.
2Cu + O2 + Heat → 2CuO.
(d) Decomposition reaction a reaction in which a single reactant breaks down to give simpler products.
Example: Decomposition of calcium carbonate to calcium oxide and carbon dioxide on heating
CaCO3(s) + Heat → CaO(s) + CO2(g)
(Limestone) (Quick lime)
(e) A reaction in which a single product is formed from two or more reactants is known as a combination reaction.
Example: Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat.
CaO(s) + H2O(l) → Ca(OH)2(aq)
(Quick lime) (Slaked lime)
32. I. Solid calcium oxide was taken in a container and water was added slowly to it.
(a) Write the observation,
(b) Write the chemical formula of the product formed.
II. What happens when carbon dioxide gas is bubbled through lime water?
(a) In a small amount
(b) In excess?
Ans. I. (a) Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat.
(b) CaO(s) + H2O(l) → Ca(OH)2(aq)
(Quick lime) (Slaked lime)
In this reaction, calcium oxide and water combine to form a single product, calcium hydroxide, and this reaction is known as a combination reaction.
II. (a) When carbon dioxide gas is bubbled through lime water in a small amount, lime water turns into milky due to the formation of insoluble calcium carbonate.
Reaction : Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)
(b) In excess, milkiness of solution of the solution of lime water disappears due to the formation of calcium bicarbonate.
Reaction:
CO2+H2O→ H2CO3
CaCO3 + H2CO3 → Ca(HCO3)2
33. I. (a) Why do you apply Paint on Iron articles?
(b)What happens chemically when quicklime is added to water.
(c) Balance the following chemical equation. MnO2 +HCl→MnCl2+Cl2+H2O.
II. Give one example each of a chemical reaction described by:
(a) evolution of gas
(b) change in colour
(c) formation of precipitate
(d) change in temperature.
(e) change in state.
Ans. I. (a) Paint is applied to the iron article to protect from rusting of iron or corrosion.
(b) When quicklime (CaO) is added to water to produce calcium hydroxide and heat.
CaO + H2O → Ca(OH)2 + heat.
(c) Balancing of chemical equation :MnO2 +HCl→MnCl2+Cl2+H2O is as follows:
MnO2 + 4HCl→MnCl2 + Cl2+ 2H2O.
II. (a) Evolution of gas - Reaction between copper and dilute sulphuric acid.
Forms copper sulphate and hydrogen gas.
b) Change in color - Reaction between blue coloured copper sulphate and iron gives a green solution of iron sulphate.
c) Formation of a precipitate - Reaction between potassium iodide and lead nitrate forms a yellow precipitate of lead iodide.
d) Change in temperature - Reaction between calcium oxide and water.
e) Change in state - Combustion of solid carbon in the presence of oxygen forms gas of CO2.
34.Balance the following equations :
(i) Hg(NO3)2 ⎯⎯⎯→Hg + NO2 + O2 heat.
(ii) NaNO3 ⎯⎯⎯→NaNO2 + O2 he
(iii) Ca + H2O ⎯⎯→ Ca(OH)2 + Heat
(iv) NaNO3 + H2SO4→ Na2SO4+ HNO3
(v) Na2CO3 + H2O + CO2 ⎯⎯→ NaHCO3
(vi) Mg + HCl ⎯⎯→ MgCl2 + H2
(vii) Na +H2O ⎯⎯→ NaOH + H2
(viii) C4H10 + O2⎯⎯→ CO2 + H2O
(ix) FeS + HCl ⎯⎯→ FeCl2 + H2S
(x) MnO2 + HCl ⎯⎯→MnCl2+H2O + Cl2
(xi) Mg3N2 + H2O ⎯⎯→ Mg(OH)2 + NH3
(xii) NH3 + O2 → N2 + H2O
(xiii) MgCl2 + Na2CO3 →NaCl+ MgCO3
(xiv) NaOH + → NaCl + NaClO + H2O
(xv) FeCl3 + NaOH → NaCl + Fe(OH)3
(xvi) NaCl + MnO2 +H2SO4→NaHSO4+ MnSO4 + H2O + Cl2
(xvii) KNO3 + H2SO4→ K2SO4 + HNO3
(xviii) PbO + HNO3 → Pb(NO3)2 +H2O
(xix) FeSO4 + NaOH → Na2SO4+ Fe(OH)2
(xx) Fe2(CO2)3 + H2SO4 →Fe2(SO4)3 + CO2 + H2O
(xxi) Ca(OH)2 + HNO3 ⎯→ Ca(NO3)2 + H2O
(xxii) BaCl2 + H2SO4 → BaSO4 + HCl
(xxiii) H2SO4 + NaOH → Na2SO4+ H2O
(xxiv) NaCl + AgNO3 → AgCl + NaNO3
(xxv) Al + Fe2O3 → Al2O3 + Fe
(xxvi) Cl2 + P4 → PCl5
(xxvii) CH4 + O2 → CO2 + H2O(xxviii) Pb(NO3)2 → PbO + NO2 + O2
(xxix) KClO3 → KCl + O2
Ans. (i) Hg(NO3)2 + heat→Hg + 2NO2 + O2
(ii) 2NaNO3 + heat→2NaNO2 + O2
(iii) CaO + H2O → Ca(OH)2 + Heat(ii) 2NaNO3 + heat→2NaNO2 + O2
(iv) 2NaNO3 + H2SO4→ Na2SO4+ 2HNO3
(v) Na2CO3 + H2O + CO2 ⎯⎯→ 2NaHCO3
(vi) Mg + 2HCl ⎯⎯→ MgCl2 + H2
(vii) 2Na + 2H2O ⎯⎯→ 2NaOH + H2
(viii) 2C4H10 + 13O2⎯⎯→ 8CO2 + 10H2O
(ix) FeS + 2HCl ⎯⎯→ FeCl2 + H2S
(x) MnO2 + 2HCl ⎯⎯→MnCl2+H2O + Cl2
(xi) Mg3N2 + 6H2O ⎯⎯→ 3Mg(OH)2 + 2NH3
(xii) 4NH3 + 3O2 → 2N2 + 6H2O
(xiii) MgCl2 + Na2CO3 → 2NaCl + MgCO3
(xiv) 2NaOH + Cl → NaCl + NaClO + H2O
(xv) FeCl3 + 3NaOH → 3NaCl + Fe(OH)3
(xvi) 2NaCl + MnO2 + 2H2SO4→ Na2SO4+ MnSO4 + 2H2O + Cl2
(xvii) 2KNO3 + H2SO4→ K2SO4 + 2HNO3
(xviii) PbO + 2HNO3 → Pb(NO3)2 +H2O
(xix) FeSO4 + 2NaOH → Na2SO4+ Fe(OH)2
(xx) Fe2(CO3)3 + 3H2SO4 →Fe2(SO4)3 + 3CO2 + 3H2O
(xxi) Ca(OH)2 + 2HNO3 ⎯→ Ca(NO3)2 + 2H2O
(xxii) BaCl2 + H2SO4 → BaSO4 + 2HCl
(xxiii) H2SO4 + 2NaOH → Na2SO4+ 2H2O
(xxiv) NaCl + AgNO3 → AgCl + NaNO3
(xxv) 2Al + Fe2O3 → Al2O3 + 2Fe
(xxvi) 10Cl2 + P4 → 4PCl5
(xxvii) CH4 + 2O2 → CO2 + 2H2O(xxviii) Pb(NO3)2 → PbO + 2NO2 + O2
(xxix) 2KClO3 → 2KCl + 3O2
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