I. Very short answer type questions:
1. What happens when calcium reacts with water?
4. Give reasons for the following:
(a) Why do aluminum sheets not corrode easily?
(b) Why is copper vessel covered with a green coating in the rainy season?
Ans. Cinnabar (HgS) is an ore of mercury. When it is heated in air, it is first converted into mercuric oxide (HgO).
2HgS(s) + 3O2 (g) → 2HgO(s) + 2SO2 (g)
Mercuric oxide is then reduced to mercury on further heating.
2HgO(s) → 2Hg(l) + O2 (g).
12. Give reasons:
(i) Sodium metal is stored under Kerosene oil.
(ii) In spite of being highly reactive aluminum is still used for making vessels utensils.
Ans. (i) Sodium is highly reactive and reacts so vigorously that they catch fire if kept in the open. Hence, to protect them and to prevent accidental fires, they are kept immersed in kerosene oil due to which sodium cannot contact with air.
(ii) In spite of being highly reactive aluminum is still used for making vessels utensils because, when aluminium exposed to the atmosphere, a protective layer of aluminium oxide is formed at the surface of the aluminium that prevents further reaction.
13. Give reasons for the following:
(i) School Bells are made up of metals.
(ii) Electrical wires are made up of copper.
Ans. (i) School Bells are made up of metals because metals are sonorous that produce a sound on striking a hard surface.
(ii) Electrical wires are made up of copper because copper is a good conductor of electricity and has high melting points.
14. (i) What do you mean by amalgam?
(ii) Give the composition of brass and bronze.
Ans. (i) If one of the metals is mercury in the alloy, then the alloy is known as an amalgam.
(ii) Brass, an alloy of copper and zinc (Cu and Zn), and bronze, an alloy of copper and tin (Cu and Sn).
16. What are the constituents of the solder alloy? Which property of solders makes it suitable for welding electrical wires?
Ans. The constituents of the solder alloy are lead and tin (Pb and Sn).
Solder alloy has a low melting point and is used for welding electrical wires together.
17. Differentiate the roasting and calcination process. Giving one example of each.
Ans. The metallic ores are converted into oxides by heating strongly in the presence of excess air. This process is known as roasting.
The carbonate ores are changed into oxides by heating strongly in limited air. This process is known as calcination. The chemical reaction that takes place during roasting and calcination of zinc ores can be shown as follows –
Roasting:
heat
2ZnS(s) + 3O2 (g) → 2ZnO(s) + 2SO2 (g)
Calcination:
heat
ZnCO3 (s) → ZnO(s) + CO2 (g)
18. Zinc is a metal found in the middle of the activity series of metals. In nature, It is found as a carbonate or ZnCO3. Mention the steps carried out for its extraction from the ore. Support with equations.
Ans. In the first step, the carbonate ores of zinc are changed into oxides by heating strongly in limited air that is the process of calcination.
Calcination
heat
ZnCO3 (s) → ZnO(s) + CO2 (g)
In the second step, the metal oxides are then reduced to the corresponding metals by using suitable reducing agents such as carbon.
Zinc oxide is heated with carbon, it is reduced to metallic zinc.
ZnO(s) + C(s) → Zn(s) + CO(g)
19. Explain the formation of ionic compound CaO with an electron dot structure. The atomic number of calcium and oxygen is 20 and 8 respectively.
Ans. The calcium atom has two electrons in its outermost shell and it requires to lose two electrons to complete its octet in the outer shell. It loses two electrons and becomes stable and there is a positive charge as calcium cation Ca2+.
On the other hand, oxygen has six electrons in its outermost shell and it requires two more electrons to complete its octet so after gaining two electrons, the oxygen atom gets a two negative charge. The bond formed in this manner by the transfer of electrons from a metal to a non-metal is known as an electrovalent bond.
Ca → Ca2+ + 2e
2,8,8,2 2,8,8
2O + e → 2O-
2, 6 2, 8
20. All Ores are minerals but all minerals are not ores. Justify the statement. Explain roasting with the help of reaction.
Ans. Minerals which contain a very high percentage of a particular metal and the metal can be profitably extracted from it are called ores so all ores are minerals but all minerals are not ores.
III Long answer type questions:
1. How is copper extracted from its ore? Explain the process of refining copper with the help of a diagram.
Ans. The copper sulphide ores converted into copper oxides by heating in the presence of excess air.
(i) A metal that is preserved in kerosene.
(ii) Lustrous colored nonmetal.
(iii) A metal that is melt while kept on the palm.
(iv) A metal which is a poor conductor of heat.
Ans. (i) Potassium K(or Na) is highly reactive and catch fire easily if kept in the air or open. Hence, to protect it and to prevent accidental fires, it is kept immersed in kerosene oil.
(ii) Iodine I is a coloured lustrous non-metal.
(iii) Gallium (Or cesium) has very low melting points. This metal will melt if you keep it on our palm.
(iv) Lead (or mercury ) is comparatively poor conductors of heat.
3. Give reasons for the following:
(i) Ionic compounds have a high melting point and boiling point
(ii) Ionic compounds conduct electricity in a molten state.
(iii) Ionic compounds are solid at room temperature and are somewhat hard.
Ans. (i) Ionic compounds have high melting and boiling points because they have strong electrovalent bond a large amount of energy is required to break the strong inter-ionic attraction.
(ii) Ionic compounds conduct electricity only in the molten state, not in solid-state because in the molten state the electrostatic forces of attraction between the oppositely charged ions are overcome due to the heat and thus, the ions move freely and conduct electricity. In solid-state ions can not move freely.
(iii) Ionic compounds are solids and are somewhat hard because of the strong force of attraction between the positive and negative ions.
4. Give reasons for the following:
(a) Metals usually do not liberate hydrogen from nitric acid.
(b) Oxides of highly reactive metals cannot be reduced by coke.
Ans. (a) Metals usually do not liberate hydrogen from nitric acid because HNO2 is a strong oxidising agent and it oxidises the H2 produced to water and itself gets reduced to nitrogen oxides. (N2O, NO, NO2).
(b) Oxides of highly reactive metals cannot be reduced by coke because coke C is less reactive than these metals due to which carbon cannot displace the metals from its oxides.
5. Illustrate the formation of bond:
(i) Sodium chloride
(ii) Magnesium chloride
(iii) Identify the ions present in this compound.
Ans. (i) The sodium atom has one electron in its outermost shell and it requires to lose one electron to complete its octet in the outer shell. It loses one electron and becomes stable and there is a positive charge as sodium cation Na+.
On the other hand, chlorine has seven electrons in its outermost shell and it requires one more electron to complete its octet so after gaining an electron, the chlorine atom gets a unit negative charge. The bond formed in this manner by the transfer of electrons from a metal to a non-metal is known as an electrovalent bond.
(ii) The magnesium atom has two electrons in its outermost shell and it requires to lose two electrons to complete its octet. It loses two electrons and becomes stable and there is a positive charge as magnesium cation Mg2+.
On the other hand, chlorine has seven electrons in its outermost shell and it requires one more electron to complete its octet so after gaining two electrons, two chlorine atoms get a unit negative charge Cl-2 The bond formed in this manner by the transfer of electrons from a metal to a non-metal are known as an electrovalent bond.
6. (a)Aluminum occurs in a combined state where gold is found in a free state in nature. Why?
(b)Define alloy. List the properties of alloys that make them useful over pure metal. Explain this fact with suitable examples.
Ans. (a) Aluminium occurs in the combined state whereas, gold occurs in the free state in nature because aluminum is more reactive than gold and hence reacts to form compounds but gold is least reactive hence it does not form a compound.
(b) An alloy is a homogeneous mixture of two or more metals, or a metal and a nonmetal. For example- Brass is an alloy of copper and zinc (Cu and Zn), bronze is an alloy of copper and tin (Cu and Sn).
Properties: (a) Alloys are harder than metal,
(b) Alloy is stronger than metal,
(c) Alloy is more resistant to corrosion,
(d) Alloy is a lower electrical conductor.
Ex - Steel is stronger, less corrosive and lower electrical conductor than iron.
7. Which method will you use to reduce the following?
(i) Oxides of less reactive metals.
(ii) Oxides of moderately reactive metals.
(iii) Oxides are highly reactive metals.
(iv) Explain by giving a suitable example.
Ans. (i) Oxides of less reactive metals can be reduced to metals by heating alone because they are very unreactive. For example, cinnabar (HgS) is an ore of mercury. When it is heated in air, it is first converted into mercuric oxide (HgO). Mercuric oxide is then reduced to mercury on further heating.
2HgO(s) 2Hg(l) + O2 (g)
(ii) Oxides of moderately reactive metals are reduced to the corresponding metals by using suitable reducing agents such as carbon. Highly reactive metals such as sodium, calcium, aluminium, etc., are also can be used as a reducing agent. For example, when zinc oxide is heated with carbon, it is reduced to metallic zinc. ZnO(s) + C(s) → Zn(s) + CO(g)
(iii) Highly reactive metals can not be obtained from their compounds by heating with carbon because these metals have more affinity for oxygen than carbon. So oxides are highly reactive metals are reduced by electrolytic reduction. For example, sodium, magnesium, and calcium are obtained by the electrolysis of their molten chlorides.
At cathode Na+ + e- → Na At anode 2Cl- → Cl2 + 2e-
8. Write a balanced equation for the reaction of
(i) Aluminum when heated in air.
(ii) Iron with steam.
(iii) Calcium with water. Name the product obtained.
Ans. (i) Aluminium when heated in air it forms aluminium oxide.
4Al + 3O2 → 2Al2O3
(Aluminium) (Aluminium oxide)
(ii) When iron react with steam it form the metal oxide and hydrogen.
3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)
(iii) When calcium react with water it produces hydrogen gas with bubbles.
Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g).
9. Describe an activity to show that rusting of iron works in the presence of air and moisture.
Ans . Take three test tubes and place clean iron nails
in each of them.
. Label these test tubes A, B and C. Pour some
water in test tube A and cork it.
. Pour boiled distilled water in test tube B, add
about 1 mL of oil and cork it. The oil will float on
water and prevent the air from dissolving in the
water.
. Put some anhydrous calcium chloride in
test tube C and cork it. Anhydrous calcium
chloride will absorb the moisture, if any, from
the air. Leave these test tubes for a few days and
then observe.w
We will observe that iron nails rust in test tube A,
but they do not rust in test tubes B and C. In the test
tube A, the nails are exposed to both air and water. 0. A metal X left in moist air for a longer time loses its shiny brown surface and gains a green coat. Why has this happened? Name and give the chemical formula of this given colored compound and identify the metal. Least two ways to prevent this process.
11. By giving one example each explain the method of obtaining the following metals from their compounds.
(i) Metal A which is low in the activity series
(ii) Metal B which is in the middle of the activity series
(iii) Metal C which is towards the top of the activity series.
Ans. (i) Metals low in the activity series are very unreactive. The oxides of these metals can be reduced to metals by heating alone. For example, cinnabar(HgS) is an ore of mercury. When it is heated in air, it is first converted into mercuric oxide (HgO). Mercuric oxide is then reduced to mercury on further heating.
2HgS(s) + 3O (g) 2HgO(s) + 2SO (g) → Heat
2HgO(s) 2Hg(l) + O2(g) → Heat.
(ii) The metals in the middle of the activity series such as iron, zinc, lead,copper, etc., are moderately reactive. These are usually present as
sulphides or carbonates in nature. The sulphide ores are converted into oxides by heating strongly in the presence of excess air. This process is known as roasting.
The carbonate ores are changed into oxides by heating strongly in limited air. This process is known as calcination. The chemical reaction that takes place during roasting and calcination of zinc ores can be shown as follows –
Roasting
2ZnS(s) + 3O2(g)→2 (g) 2ZnO(s) + 2SO2 (g) → Heat
Calcination
ZnCO (s)→ ZnO(s) + CO2(g) → Heat
The metal oxides are then reduced to the corresponding metals by
using suitable reducing agents such as carbon. For example, when zinc oxide is heated with carbon, it is reduced to metallic zinc.
ZnO(s) + C(s) → Zn(s) + CO(g).
(iii) The metals high up in the reactivity series are very reactive and cannot be obtained from their compounds by heating with carbon because these metals have more affinity for oxygen than carbon. These metals are obtained by electrolytic reduction. For example, sodium is obtained by the electrolysis of their molten chlorides. The metals are deposited at the cathode (the negatively charged electrode), whereas, chlorine is liberated at the anode (the positively charged electrode). The reactions are – At cathode Na+ + e– → Na At anode 2Cl– → Cl2 + 2e–
12. Write a balanced chemical equation for the following reaction:
(i) When copper is heated in the air
(ii) When Aluminum is heated in the air
(iii) When Aluminum oxide reacts with Sodium Hydroxide.
Ans. (i) When copper is heated in air, it combines with oxygen to form a black copper (II) oxide.
2Cu + O2 → 2CuO
(Copper) (Copper(II) oxide)
(ii) When Aluminium is heated in air, aluminium forms aluminium oxide.
4Al + 3O2→ 2Al2O3
(Aluminium) (Aluminium oxide)(iii) When aluminium oxides react with sodium hydroxide to produce salts and water .
Al2O3 + 2NaOH → 2NaAlO2 + H2O
(Aluminium (Sodium
oxide) aluminate)
13. Compare the properties of a typical metal and a nonmetal on the basis of the following:
(i) Nature of the oxides formed by them.
(ii) Conductivity.
Ans. (i) Most metals produce basic oxides when dissolving in water and metal oxides are insoluble in water but some of these dissolve in water to form alkalis.
Most non-metals produce acidic oxides when dissolving in water and most nonmetallic oxides are soluble in water to form acids.
(ii) Metals are a good conductor of electricity and heat but nonmetals are bad conductors of electricity and heat except graphite. Graphite is a nonmetal but it conducts electricity.
14. In a thermite reaction compound of iron reacts with a metal.
(i) Name the metal used in this reaction.
(ii) After completion of this reaction, a metal is obtained in the molten state. Identify the metal.
(iii) Represent these reactions in the form of a balanced chemical equation. Mention the most common use of this reaction.
(II)Aluminum can be used to store a ferrous sulfate solution. It is observed that in few days holes appear in the can. Explain the observation and write chemical equations to support your answer.
Ans. (I) (i) Aluminium is the metal that is used with a compound of iron in a thermit reaction.
(ii) Iron Fe metal is obtained in the molten state in this exothermic reaction which is known as thermit reaction.
(iii) A balanced chemical reaction is :
Fe2O3(s) + 2Al(s) → 2Fe(l) + Al2O3(s) + Heat.
These displacement reactions are highly exothermic. The amount of heat evolved is so large that the metals are produced in the molten state so this reaction is used to join railway tracks or cracked machine parts.
(II) Aluminium is present above the iron in reactivity series so aluminum is more reactive than iron. Because of high reactivity aluminium displaces iron from its sulphate solution and produce aluminium sulphate solution. That is why holes appeared.
2Al + 3FeSO4 = Al2(SO4)3 +3 Fe
15. Zn is the metal that lies in the middle of the activity series, these metals are extracted from its sulfide ore. Outline the steps involved in the process of extraction of zinc metal with the help of a balanced chemical equation for each staple.
Ans. The metal in the middle of the activity series such as zinc is moderately reactive. This is usually present as sulphides or carbonates in nature.
It is easier to obtain metal from its oxide, as compared to its sulphides and carbonates.
The sulphide ores are converted into oxides by heating strongly in the presence of excess air and the carbonate ores are changed into oxides by heating strongly in limited air.
Roasting 2ZnS(s) + 3O2 (g)→ (Heat) 2ZnO(s) + 2SO2(g)
ZnCO2 (s) → (Heat) ZnO(s) + CO2(g)
The metal oxides are then reduced to the corresponding metals by using suitable reducing agents such as carbon.
ZnO(s) + C(s) → Zn(s) + CO(g).
1. What happens when calcium reacts with water?
Ans. Calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of the metal. It also produces calcium hydroxide.
Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g)
Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g)
2. Generally, metals react with acids to give salt and hydrogen gas. Which acids do not give hydrogen gas on reacting with metals?
Ans. Nitric acid does not give hydrogen gas on reacting with metals.
Ans. Gold and platinum are the two very less reactive metals that exist in their native nature.
Ans. Copper (others are Ag, Au, Zn, etc) is a metal that is refined by electrolytic refining.
Ans. Hg is a metal that is liquid at room temperature, Ag is a metal that is refined by electrolytic refining and iodin is a lustrous none metal.
Ans. Mg, Cu, and Zn are the more reactive metals than silver by which silver metal can be displaced from its salt solution.
Ans. (i) The atomic number is 10.
Hence it is Neon. Since it has only 8 valence electrons and valency is 0, therefore, it must be inert.
(ii) The atomic number is 17.
Hence it is Cl. Since it has only 7 valence electrons and valency is -1, therefore, it must be a non-metal.
(iii) The atomic number is 12.
Hence it is Mg. Since it has only 2 valence electrons and valency is +2 therefore, it must be metal.
It is a stable element because it has 8 electrons in its last shell.
Ans. Aluminium oxide and zinc oxide are the two amphoteric oxides which have both acidic as well as basic behavior.
Ans. Graphite is a non-metal that conducts electricity.
Ans. Br bromine is a nonmetal which is liquid.
Ans. Silver articles become black after some time when exposed to air because it reacts with sulphur in the air to form a coating of silver sulphide.
Ans. When ZnCO3 is heated in the absence of air, ZnO and CO2 are formed.
ZnCO3 (s)→ ZnO(s) + CO2(g)
Ans. An alloy is a homogeneous mixture of two or more metals, or a metal and a nonmetal.
Ans . Nickel and chromium
Ans. Hydrogen gas.
Ans. Silver is the best conductor of heat.
Ans. Two physical properties of gold are ductility and lustrous which are of extreme use of Jewelers.
Ans. Hg and Br are the metal and non-metal respectively which exists in a liquid state at room temperature.
Ans. Metallic oxides are basic in nature and non-metallic oxides are acidic in nature.
Ans. Mg and Mn are the metals that react with a very dilute HNO3 to evolved hydrogen gas.
Ans. Gallium (Ga).
Ans. The bond formed by the transfer of electrons from a metal to a non-metal is ionic in nature.
Ans. X is metal because of a metallic oxide is basic in nature and the base turns let litmus blue.
Ans. Metallurgy is the branch of science and technology concerned with the properties of metals and their production and purification.
Ans. When the ores are converted into oxides by heating strongly in the presence of excess air, this process is known as roasting.
When the carbonate ores are changed into oxides by heating strongly in limited air, this process is known as calcination.
Ans. Iodine a non-metal that is lustrous and Sodium a metal that is nonlustrous.
Ans. To prevent rusting, we apply paint on iron articles.
Ans. A thermite reaction is an exothermic reduction-oxidation reaction in which a metallic oxide reacts with metallic powder produce a large amount of heat.
And. Aluminum and copper metals used for making cooking vessels because of are good conductors of heat and have high melting points.
Ans. Aluminium oxide reacts in the following manner with acids and bases –
Al2O3 + 6HCl → 2AlCl3 + 3H2O
(Aluminium chloride)
Al2O3 + 2NaOH → 2NaAlO2 + H2O
(Sodium aluminate)
Ans. Aqua regia (royal) water is a mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1. It can dissolve gold, even though neither of these acids can do so alone. Aqua regia is a highly corrosive, fuming liquid. It is one of the few reagents that are able to dissolve gold and platinum.
Ans. The elements or compounds, which occur naturally in the earth’s crust, are known as minerals.
At some places, minerals contain a very high percentage of a particular metal and the metal can be profitably extracted from it. These minerals are called ores.
Ores mined from the earth are usually contaminated with large amounts of impurities such as soil, sand, etc., called gangue.
Ans. Galvanization is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc.
II. Short answer type questions:
Ans. Mg, Cu, and Zn are the more reactive metals than silver by which silver metal can be displaced from its salt solution.
Ans. (i) The atomic number is 10.
Hence it is Neon. Since it has only 8 valence electrons and valency is 0, therefore, it must be inert.
(ii) The atomic number is 17.
Hence it is Cl. Since it has only 7 valence electrons and valency is -1, therefore, it must be a non-metal.
(iii) The atomic number is 12.
Hence it is Mg. Since it has only 2 valence electrons and valency is +2 therefore, it must be metal.
It is a stable element because it has 8 electrons in its last shell.
Ans. Aluminium oxide and zinc oxide are the two amphoteric oxides which have both acidic as well as basic behavior.
Ans. Graphite is a non-metal that conducts electricity.
Ans. Br bromine is a nonmetal which is liquid.
Ans. Silver articles become black after some time when exposed to air because it reacts with sulphur in the air to form a coating of silver sulphide.
Ans. When ZnCO3 is heated in the absence of air, ZnO and CO2 are formed.
ZnCO3 (s)→ ZnO(s) + CO2(g)
Ans. An alloy is a homogeneous mixture of two or more metals, or a metal and a nonmetal.
Ans . Nickel and chromium
Ans. Hydrogen gas.
Ans. Silver is the best conductor of heat.
Ans. Two physical properties of gold are ductility and lustrous which are of extreme use of Jewelers.
Ans. Hg and Br are the metal and non-metal respectively which exists in a liquid state at room temperature.
Ans. Metallic oxides are basic in nature and non-metallic oxides are acidic in nature.
Ans. Mg and Mn are the metals that react with a very dilute HNO3 to evolved hydrogen gas.
Ans. Gallium (Ga).
Ans. The bond formed by the transfer of electrons from a metal to a non-metal is ionic in nature.
Ans. X is metal because of a metallic oxide is basic in nature and the base turns let litmus blue.
Ans. Metallurgy is the branch of science and technology concerned with the properties of metals and their production and purification.
Ans. When the ores are converted into oxides by heating strongly in the presence of excess air, this process is known as roasting.
When the carbonate ores are changed into oxides by heating strongly in limited air, this process is known as calcination.
Ans. Iodine a non-metal that is lustrous and Sodium a metal that is nonlustrous.
Ans. To prevent rusting, we apply paint on iron articles.
Ans. A thermite reaction is an exothermic reduction-oxidation reaction in which a metallic oxide reacts with metallic powder produce a large amount of heat.
And. Aluminum and copper metals used for making cooking vessels because of are good conductors of heat and have high melting points.
Ans. Aluminium oxide reacts in the following manner with acids and bases –
Al2O3 + 6HCl → 2AlCl3 + 3H2O
(Aluminium chloride)
Al2O3 + 2NaOH → 2NaAlO2 + H2O
(Sodium aluminate)
Ans. Aqua regia (royal) water is a mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1. It can dissolve gold, even though neither of these acids can do so alone. Aqua regia is a highly corrosive, fuming liquid. It is one of the few reagents that are able to dissolve gold and platinum.
Ans. The elements or compounds, which occur naturally in the earth’s crust, are known as minerals.
At some places, minerals contain a very high percentage of a particular metal and the metal can be profitably extracted from it. These minerals are called ores.
Ores mined from the earth are usually contaminated with large amounts of impurities such as soil, sand, etc., called gangue.
Ans. Galvanization is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc.
II. Short answer type questions:
Ans. Ionic compounds are held by strong electrostatic forces of attraction and a considerable amount of energy is required to break the strong inter-ionic attraction so ionic compounds have high melting and boiling points.
Ana. Corrosion is a prosses of corroding that converts a refined metal to a more chemically-
Ex- Ag corrode to silver sulfide, Cu corrode to copper carbonate and Fe corrode to rust (iron oxide).
Ans. Iron is more reactive than copper so due to displacement reaction, the blue colour of copper sulphate solution is changed to the light green colour of iron sulphate and the silver colour of iron nail is changed to reddish-brown colour due to a coating of copper metal on the nail.
4. Give reasons for the following:
(a) Why do aluminum sheets not corrode easily?
(b) Why is copper vessel covered with a green coating in the rainy season?
Ans. (a) When aluminium exposed to the atmosphere, a protective layer of aluminium oxide is formed at the surface of the metal and hence inhibits any further reaction of the metal with the surrounding. So aluminum sheets do not corrode easily.
(b) Copper vessel reacts with CO2 and moisture (H2O) present in the atmosphere in the rainy season and formed a basic copper carbonate layer [CuCO3 Cu(OHO2 ] which is green in colour.
Ans. Calcium and magnesium start floating after sometime when immersed in water and it is because of the bubbles of hydrogen gas formed when they react with cold and hot water respectively and stick to the surface of the metal.
Ans. The copper sulphide ores converted into copper oxides by heating in the presence of excess air.
2Cu2S + 3O2(g)→ 2CuO(s) + 2SO2 (g)
Copper oxide is then reduced to copper on further heating with copper sulphide.
CuO(s) + Cu2S(s) → Cu(s) + CO2(g)
Ans. Some metals combine with oxygen to form basic oxides and when these oxides show the properties of both basic, as well as acidic oxides, are known as amphoteric oxides. Aluminium oxide and zinc oxide are the amphoteric oxides that are when react with acid and base formed salt and water.
Ans. The compounds formed by the transfer of electrons from a metal to a non-metal are known as ionic compounds or electrovalent compounds.
Ionic compounds conduct electricity only in the molten state, not in solid-state because in the molten state the electrostatic forces of attraction between the oppositely charged ions are overcome due to the heat and thus, the ions move freely and conduct electricity but ionic compounds in the solid-state do not conduct electricity because the movement of ions in the solid is not possible due to their rigid structure.
Ans. During chemical reaction after losing electrons, Mg gets a positive charge and by gaining electrons O gets a negative charge, so Mg is the cation and O is the anion.
Ionic compounds are solid due to the strong force of attraction between the positive and negative ions that form a strong ionic bond.
Ans. The metals produced by various reduction processes are not very pure. They contain impurities, which must be removed to obtain pure metals. The refining of metals is the process by which these impurities can be removed. Electrolytic refining is the most widely used method for refining impure metals.
Ans. Cinnabar (HgS) is an ore of mercury. When it is heated in air, it is first converted into mercuric oxide (HgO).
2HgS(s) + 3O2 (g) → 2HgO(s) + 2SO2 (g)
Mercuric oxide is then reduced to mercury on further heating.
2HgO(s) → 2Hg(l) + O2 (g).
12. Give reasons:
(i) Sodium metal is stored under Kerosene oil.
(ii) In spite of being highly reactive aluminum is still used for making vessels utensils.
Ans. (i) Sodium is highly reactive and reacts so vigorously that they catch fire if kept in the open. Hence, to protect them and to prevent accidental fires, they are kept immersed in kerosene oil due to which sodium cannot contact with air.
(ii) In spite of being highly reactive aluminum is still used for making vessels utensils because, when aluminium exposed to the atmosphere, a protective layer of aluminium oxide is formed at the surface of the aluminium that prevents further reaction.
13. Give reasons for the following:
(i) School Bells are made up of metals.
(ii) Electrical wires are made up of copper.
Ans. (i) School Bells are made up of metals because metals are sonorous that produce a sound on striking a hard surface.
(ii) Electrical wires are made up of copper because copper is a good conductor of electricity and has high melting points.
14. (i) What do you mean by amalgam?
(ii) Give the composition of brass and bronze.
Ans. (i) If one of the metals is mercury in the alloy, then the alloy is known as an amalgam.
(ii) Brass, an alloy of copper and zinc (Cu and Zn), and bronze, an alloy of copper and tin (Cu and Sn).
16. What are the constituents of the solder alloy? Which property of solders makes it suitable for welding electrical wires?
Ans. The constituents of the solder alloy are lead and tin (Pb and Sn).
Solder alloy has a low melting point and is used for welding electrical wires together.
17. Differentiate the roasting and calcination process. Giving one example of each.
Ans. The metallic ores are converted into oxides by heating strongly in the presence of excess air. This process is known as roasting.
The carbonate ores are changed into oxides by heating strongly in limited air. This process is known as calcination. The chemical reaction that takes place during roasting and calcination of zinc ores can be shown as follows –
Roasting:
heat
2ZnS(s) + 3O2 (g) → 2ZnO(s) + 2SO2 (g)
Calcination:
heat
ZnCO3 (s) → ZnO(s) + CO2 (g)
18. Zinc is a metal found in the middle of the activity series of metals. In nature, It is found as a carbonate or ZnCO3. Mention the steps carried out for its extraction from the ore. Support with equations.
Ans. In the first step, the carbonate ores of zinc are changed into oxides by heating strongly in limited air that is the process of calcination.
Calcination
heat
ZnCO3 (s) → ZnO(s) + CO2 (g)
In the second step, the metal oxides are then reduced to the corresponding metals by using suitable reducing agents such as carbon.
Zinc oxide is heated with carbon, it is reduced to metallic zinc.
ZnO(s) + C(s) → Zn(s) + CO(g)
19. Explain the formation of ionic compound CaO with an electron dot structure. The atomic number of calcium and oxygen is 20 and 8 respectively.
Ans. The calcium atom has two electrons in its outermost shell and it requires to lose two electrons to complete its octet in the outer shell. It loses two electrons and becomes stable and there is a positive charge as calcium cation Ca2+.
On the other hand, oxygen has six electrons in its outermost shell and it requires two more electrons to complete its octet so after gaining two electrons, the oxygen atom gets a two negative charge. The bond formed in this manner by the transfer of electrons from a metal to a non-metal is known as an electrovalent bond.
Ca → Ca2+ + 2e
2,8,8,2 2,8,8
2O + e → 2O-
2, 6 2, 8
20. All Ores are minerals but all minerals are not ores. Justify the statement. Explain roasting with the help of reaction.
Ans. Minerals which contain a very high percentage of a particular metal and the metal can be profitably extracted from it are called ores so all ores are minerals but all minerals are not ores.
III Long answer type questions:
1. How is copper extracted from its ore? Explain the process of refining copper with the help of a diagram.
Ans. The copper sulphide ores converted into copper oxides by heating in the presence of excess air.
2Cu2S + 3O2(g)→ 2CuO(s) + 2SO2 (g)
Copper oxide is then reduced to copper on further heating with copper sulphide.
CuO(s) + Cu2S(s) → Cu(s) + CO2(g)
2. Name the following:
(i) A metal that is preserved in kerosene.
(ii) Lustrous colored nonmetal.
(iii) A metal that is melt while kept on the palm.
(iv) A metal which is a poor conductor of heat.
Ans. (i) Potassium K(or Na) is highly reactive and catch fire easily if kept in the air or open. Hence, to protect it and to prevent accidental fires, it is kept immersed in kerosene oil.
(ii) Iodine I is a coloured lustrous non-metal.
(iii) Gallium (Or cesium) has very low melting points. This metal will melt if you keep it on our palm.
(iv) Lead (or mercury ) is comparatively poor conductors of heat.
3. Give reasons for the following:
(i) Ionic compounds have a high melting point and boiling point
(ii) Ionic compounds conduct electricity in a molten state.
(iii) Ionic compounds are solid at room temperature and are somewhat hard.
Ans. (i) Ionic compounds have high melting and boiling points because they have strong electrovalent bond a large amount of energy is required to break the strong inter-ionic attraction.
(ii) Ionic compounds conduct electricity only in the molten state, not in solid-state because in the molten state the electrostatic forces of attraction between the oppositely charged ions are overcome due to the heat and thus, the ions move freely and conduct electricity. In solid-state ions can not move freely.
(iii) Ionic compounds are solids and are somewhat hard because of the strong force of attraction between the positive and negative ions.
4. Give reasons for the following:
(a) Metals usually do not liberate hydrogen from nitric acid.
(b) Oxides of highly reactive metals cannot be reduced by coke.
Ans. (a) Metals usually do not liberate hydrogen from nitric acid because HNO2 is a strong oxidising agent and it oxidises the H2 produced to water and itself gets reduced to nitrogen oxides. (N2O, NO, NO2).
(b) Oxides of highly reactive metals cannot be reduced by coke because coke C is less reactive than these metals due to which carbon cannot displace the metals from its oxides.
5. Illustrate the formation of bond:
(i) Sodium chloride
(ii) Magnesium chloride
(iii) Identify the ions present in this compound.
Ans. (i) The sodium atom has one electron in its outermost shell and it requires to lose one electron to complete its octet in the outer shell. It loses one electron and becomes stable and there is a positive charge as sodium cation Na+.
On the other hand, chlorine has seven electrons in its outermost shell and it requires one more electron to complete its octet so after gaining an electron, the chlorine atom gets a unit negative charge. The bond formed in this manner by the transfer of electrons from a metal to a non-metal is known as an electrovalent bond.
(ii) The magnesium atom has two electrons in its outermost shell and it requires to lose two electrons to complete its octet. It loses two electrons and becomes stable and there is a positive charge as magnesium cation Mg2+.
On the other hand, chlorine has seven electrons in its outermost shell and it requires one more electron to complete its octet so after gaining two electrons, two chlorine atoms get a unit negative charge Cl-2 The bond formed in this manner by the transfer of electrons from a metal to a non-metal are known as an electrovalent bond.
(iii) In sodium chloride, Na+ is a cation and Ca- is an anion and in magnesium chloride, Mg2+ is a cation and Cl- is an anion.
6. (a)Aluminum occurs in a combined state where gold is found in a free state in nature. Why?
(b)Define alloy. List the properties of alloys that make them useful over pure metal. Explain this fact with suitable examples.
Ans. (a) Aluminium occurs in the combined state whereas, gold occurs in the free state in nature because aluminum is more reactive than gold and hence reacts to form compounds but gold is least reactive hence it does not form a compound.
(b) An alloy is a homogeneous mixture of two or more metals, or a metal and a nonmetal. For example- Brass is an alloy of copper and zinc (Cu and Zn), bronze is an alloy of copper and tin (Cu and Sn).
Properties: (a) Alloys are harder than metal,
(b) Alloy is stronger than metal,
(c) Alloy is more resistant to corrosion,
(d) Alloy is a lower electrical conductor.
Ex - Steel is stronger, less corrosive and lower electrical conductor than iron.
7. Which method will you use to reduce the following?
(i) Oxides of less reactive metals.
(ii) Oxides of moderately reactive metals.
(iii) Oxides are highly reactive metals.
(iv) Explain by giving a suitable example.
Ans. (i) Oxides of less reactive metals can be reduced to metals by heating alone because they are very unreactive. For example, cinnabar (HgS) is an ore of mercury. When it is heated in air, it is first converted into mercuric oxide (HgO). Mercuric oxide is then reduced to mercury on further heating.
2HgO(s) 2Hg(l) + O2 (g)
(ii) Oxides of moderately reactive metals are reduced to the corresponding metals by using suitable reducing agents such as carbon. Highly reactive metals such as sodium, calcium, aluminium, etc., are also can be used as a reducing agent. For example, when zinc oxide is heated with carbon, it is reduced to metallic zinc. ZnO(s) + C(s) → Zn(s) + CO(g)
(iii) Highly reactive metals can not be obtained from their compounds by heating with carbon because these metals have more affinity for oxygen than carbon. So oxides are highly reactive metals are reduced by electrolytic reduction. For example, sodium, magnesium, and calcium are obtained by the electrolysis of their molten chlorides.
At cathode Na+ + e- → Na At anode 2Cl- → Cl2 + 2e-
8. Write a balanced equation for the reaction of
(i) Aluminum when heated in air.
(ii) Iron with steam.
(iii) Calcium with water. Name the product obtained.
Ans. (i) Aluminium when heated in air it forms aluminium oxide.
4Al + 3O2 → 2Al2O3
(Aluminium) (Aluminium oxide)
(ii) When iron react with steam it form the metal oxide and hydrogen.
3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)
(iii) When calcium react with water it produces hydrogen gas with bubbles.
Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g).
9. Describe an activity to show that rusting of iron works in the presence of air and moisture.
Ans . Take three test tubes and place clean iron nails
in each of them.
. Label these test tubes A, B and C. Pour some
water in test tube A and cork it.
. Pour boiled distilled water in test tube B, add
about 1 mL of oil and cork it. The oil will float on
water and prevent the air from dissolving in the
water.
. Put some anhydrous calcium chloride in
test tube C and cork it. Anhydrous calcium
chloride will absorb the moisture, if any, from
the air. Leave these test tubes for a few days and
then observe.w
We will observe that iron nails rust in test tube A,
but they do not rust in test tubes B and C. In the test
tube A, the nails are exposed to both air and water. 0. A metal X left in moist air for a longer time loses its shiny brown surface and gains a green coat. Why has this happened? Name and give the chemical formula of this given colored compound and identify the metal. Least two ways to prevent this process.
11. By giving one example each explain the method of obtaining the following metals from their compounds.
(i) Metal A which is low in the activity series
(ii) Metal B which is in the middle of the activity series
(iii) Metal C which is towards the top of the activity series.
Ans. (i) Metals low in the activity series are very unreactive. The oxides of these metals can be reduced to metals by heating alone. For example, cinnabar(HgS) is an ore of mercury. When it is heated in air, it is first converted into mercuric oxide (HgO). Mercuric oxide is then reduced to mercury on further heating.
2HgS(s) + 3O (g) 2HgO(s) + 2SO (g) → Heat
2HgO(s) 2Hg(l) + O2(g) → Heat.
(ii) The metals in the middle of the activity series such as iron, zinc, lead,copper, etc., are moderately reactive. These are usually present as
sulphides or carbonates in nature. The sulphide ores are converted into oxides by heating strongly in the presence of excess air. This process is known as roasting.
The carbonate ores are changed into oxides by heating strongly in limited air. This process is known as calcination. The chemical reaction that takes place during roasting and calcination of zinc ores can be shown as follows –
Roasting
2ZnS(s) + 3O2(g)→2 (g) 2ZnO(s) + 2SO2 (g) → Heat
Calcination
ZnCO (s)→ ZnO(s) + CO2(g) → Heat
The metal oxides are then reduced to the corresponding metals by
using suitable reducing agents such as carbon. For example, when zinc oxide is heated with carbon, it is reduced to metallic zinc.
ZnO(s) + C(s) → Zn(s) + CO(g).
(iii) The metals high up in the reactivity series are very reactive and cannot be obtained from their compounds by heating with carbon because these metals have more affinity for oxygen than carbon. These metals are obtained by electrolytic reduction. For example, sodium is obtained by the electrolysis of their molten chlorides. The metals are deposited at the cathode (the negatively charged electrode), whereas, chlorine is liberated at the anode (the positively charged electrode). The reactions are – At cathode Na+ + e– → Na At anode 2Cl– → Cl2 + 2e–
12. Write a balanced chemical equation for the following reaction:
(i) When copper is heated in the air
(ii) When Aluminum is heated in the air
(iii) When Aluminum oxide reacts with Sodium Hydroxide.
Ans. (i) When copper is heated in air, it combines with oxygen to form a black copper (II) oxide.
2Cu + O2 → 2CuO
(Copper) (Copper(II) oxide)
(ii) When Aluminium is heated in air, aluminium forms aluminium oxide.
4Al + 3O2→ 2Al2O3
(Aluminium) (Aluminium oxide)(iii) When aluminium oxides react with sodium hydroxide to produce salts and water .
Al2O3 + 2NaOH → 2NaAlO2 + H2O
(Aluminium (Sodium
oxide) aluminate)
13. Compare the properties of a typical metal and a nonmetal on the basis of the following:
(i) Nature of the oxides formed by them.
(ii) Conductivity.
Ans. (i) Most metals produce basic oxides when dissolving in water and metal oxides are insoluble in water but some of these dissolve in water to form alkalis.
Most non-metals produce acidic oxides when dissolving in water and most nonmetallic oxides are soluble in water to form acids.
(ii) Metals are a good conductor of electricity and heat but nonmetals are bad conductors of electricity and heat except graphite. Graphite is a nonmetal but it conducts electricity.
14. In a thermite reaction compound of iron reacts with a metal.
(i) Name the metal used in this reaction.
(ii) After completion of this reaction, a metal is obtained in the molten state. Identify the metal.
(iii) Represent these reactions in the form of a balanced chemical equation. Mention the most common use of this reaction.
(II)Aluminum can be used to store a ferrous sulfate solution. It is observed that in few days holes appear in the can. Explain the observation and write chemical equations to support your answer.
Ans. (I) (i) Aluminium is the metal that is used with a compound of iron in a thermit reaction.
(ii) Iron Fe metal is obtained in the molten state in this exothermic reaction which is known as thermit reaction.
(iii) A balanced chemical reaction is :
Fe2O3(s) + 2Al(s) → 2Fe(l) + Al2O3(s) + Heat.
These displacement reactions are highly exothermic. The amount of heat evolved is so large that the metals are produced in the molten state so this reaction is used to join railway tracks or cracked machine parts.
(II) Aluminium is present above the iron in reactivity series so aluminum is more reactive than iron. Because of high reactivity aluminium displaces iron from its sulphate solution and produce aluminium sulphate solution. That is why holes appeared.
2Al + 3FeSO4 = Al2(SO4)3 +3 Fe
15. Zn is the metal that lies in the middle of the activity series, these metals are extracted from its sulfide ore. Outline the steps involved in the process of extraction of zinc metal with the help of a balanced chemical equation for each staple.
Ans. The metal in the middle of the activity series such as zinc is moderately reactive. This is usually present as sulphides or carbonates in nature.
It is easier to obtain metal from its oxide, as compared to its sulphides and carbonates.
The sulphide ores are converted into oxides by heating strongly in the presence of excess air and the carbonate ores are changed into oxides by heating strongly in limited air.
Roasting 2ZnS(s) + 3O2 (g)→ (Heat) 2ZnO(s) + 2SO2(g)
ZnCO2 (s) → (Heat) ZnO(s) + CO2(g)
The metal oxides are then reduced to the corresponding metals by using suitable reducing agents such as carbon.
ZnO(s) + C(s) → Zn(s) + CO(g).
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