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Solutions to In Text Questions of NCERT Class 10 Science Chapter 3 Metals and Non-metals
Page 40:
1. Give an example of a metal which
(i) is a liquid at room temperature.
(ii) can be easily cut with a knife.
(iii) is the best conductor of heat.
(iv) is a poor conductor of heat.
Answer:
(i) Mercury is a liquid at room temperature.
(ii) Sodium can easily be cut with a knife.
(iii) Silver is the best conductor of heat.
(iv) Lead is a poor conductor of heat.
2. Explain the meanings of malleable and ductile.
Answer:
Substances that can be beaten into thin sheets. For example, gold and silver are the most malleable metals.
The ability of substances to be drawn into thin wired in known as ductility. For example, gold, copper etc.
Page 46:
1. Why is sodium kept immersed in kerosene oil?
Answer:
Sodium is one of the most reactive metals and catches fire by reacting vigorously with oxygen if kept in the open. Hence, to protect the metal and also to prevent accidental fires, they are kept immersed in kerosene oil.
2. Write equations for the reactions of
(i) iron with steam
(ii) calcium and potassium with water
Answer:
(i) iron with steam
Iron reacts with steam to form ferric oxide and hydrogen gas.
3Fe(s) + 4H2O(g) —> Fe3O4(s) + 4H2(g)
(ii) calcium and potassium with water
Calcium reacts with water to form calcium hydroxide and hydrogen:
Ca(s) + 2H2O(l) —> Ca(OH)2(aq) + H2(g)
Potassium reacts violently with cold water to produce potassium hydroxide, hydrogen gas and heat.
2K(s) + 2H2O(l) —> 2KOH(aq) + H2(g) + heat energy
3. Samples of four metals A, B, C and D were taken and added to the following solution one by one. The results obtained have been tabulated as follows.
| Metal | Iron(II) Sulphate | Copper(II) sulphate | Zinc sulphate | Silver nitrate |
| A | No reaction | Displacement | ||
| B | Displacement | No reaction | ||
| C | No reaction | No reaction | No reaction | Displacement |
| D | No reaction | No reaction | No reaction | No reaction |
Use the Table above to answer the following questions about metals A, B, C and D.
(i) Which is the most reactive metal?
(ii) What would you observe if B is added to a solution of Copper(II) sulphate?
(iii) Arrange the metals A, B, C and D in the order of decreasing reactivity.
Answer:
(i) Among iron, copper, zinc and silver, iron is highest in the reactivity series. Since B is the only metal among A, B, C, D that displaces iron from iron(II) sulphate, we conclude B is the most reactive metal.
(ii) When B is added to a solution of Copper(II) sulphate, a displacement reaction will happen because B is more reactive than copper. The blue colour of the copper sulphate solution will fade and a brown deposit of copper will form on metal B.
(iii) Metal B is the most reactive metal because it displaces iron from iron(II) sulphate. Iron is followed by zinc and then copper in the reactivity series. None of the metals react with zinc but A displaces copper from copper sulphate, hence we conclude that A is the second most reactive metal. Among iron, copper, zinc and silver, silver is the lowest in the reactivity series. C displaces silver from silver nitrate and hence is the third most reactive metal. D does not react with any of the solutions, making it the lest reactive metal. The metals A, B, C and D in the order of decreasing reactivity are: B > A > C > D.
4. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H2SO4.
Answer:
Hydrogen gas is produced when dilute hydrochloric acid is added to a reactive metal.
The chemical reaction that results when iron reacts with dilute H2SO4 is:
Fe(s) + H2SO4(aq) —> FeSO4(aq) + H2(g)
5. What would you observe when zinc is added to a solution of iron(II) sulphate? Write the chemical reaction that takes place.
Answer:
Since zinc is more reactive than iron, it will displace iron from green iron(II) sulphate to form colourless zinc sulphate. The chemical reaction is:
Zn + FeSO4 —> ZnSO4 + Fe
Page 49:
1. (i) Write the electron-dot structures for sodium, oxygen and magnesium.
(ii) Show the formation of Na2O and MgO by the transfer of electrons.
(iii) What are the ions present in these compounds?
Answer:
(i) The electron-dot structures for sodium, oxygen and magnesium are as follows:
(ii) The formation of Na2O and MgO by the transfer of electrons are as follows:
(iii) The ions present in Na2O are Na+ and O2-. The ions present in MgO are Mg2+ and O2-.
2. Why do ionic compounds have high melting points?
Answer:
Ionic compound consist of positive and negative ions and due to opposite charge there is strong electrostatic force of attraction between them. A considerable amount of energy is required to break the strong inter-ionic attraction and hence ionic compounds have high melting points.
Page 53:
1. Define the following terms.
(i) Mineral
(ii) Ore
(iii) Gangue
Answer:
(i) Mineral
Minerals are elements or compounds, which occur naturally in the earth’s crust.
(ii) Ore
Ores are minerals which contain a very high percentage of a particular metal and the metal can be profitably extracted from it.
(iii) Gangue
Gangue are the impurities such as soil, sand, etc which contaminate the ores mined from the earth.
2. Name two metals which are found in nature in the free state.
Answer:
Gold and silver are found in nature in the free state because they are least reactive.
3. What chemical process is used for obtaining a metal from its oxide?
Answer:
Metal oxides can be reduced to metals using carbon. For example, when zinc oxide id heated with carbon, it is reduced to zinc metal: ZnO(s) + C(s) —> Zn(s) + CO(g)
Also, displacement reactions using highly reactive metals can be used. For example, when manganese oxide is heated with aluminium powder, molten manganese metal is obtained: 3MnO2(s) + 4Al(s) —> 3Mn(l) + 2Al2O3(s) + Heat
Page 55:
1. Metallic oxides of zinc, magnesium and copper were heated with the following metals.
| Metal | Zinc | Magnesium | Copper |
| Zinc oxide | |||
| Magnesium oxide | |||
| Copper oxide |
In which cases will you find displacement reactions taking place?
Answer:
Magnesium is the most reactive metal, followed by zinc and then copper. Hence, magnesium will displacement zinc and copper from zinc oxide and copper oxide respectively. Also, zinc will displace copper from copper oxide because zinc is more reactive than copper. Therefore, we get the following table:
| Metal | Zinc | Magnesium | Copper |
| Zinc oxide | – | Displacement | – |
| Magnesium oxide | – | – | – |
| Copper oxide | Displacement | Displacement | – |
2. Which metals do not corrode easily?
Answer:
Gold and tin are metals which do not corrode easily because they are not reactive. They do not react with oxygen, water and acids to form new compounds.
3. What are alloys?
Answer:
An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal. For example, brass is an alloy of copper and zinc (Cu and Zn), and bronze is an alloy of copper and tin (Cu and Sn).
Solutions to Exercises (Page No 56) of NCERT Class 10 Science Chapter 3 Metals and Non-metals
1. Which of the following pairs will give displacement reactions?
(a) NaCl solution and copper metal
(b) MgCl2 solution and aluminium metal
(c) FeSO4 solution and silver metal
(d) AgNO3 solution and copper metal
Answer: (d) AgNO3 solution and copper metal
Copper is higher in the reactivity series than silver and hence will displace silver from AgNO3 solution. The following is the reaction: Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2Ag(s)
2. Which of the following methods is suitable for preventing an iron frying pan from rusting?
(a) Applying grease
(b) Applying paint
(c) Applying a coating of zinc
(d) All of the above
Answer: (c) Applying a coating of zinc
Applying grease and paint are not suitable. This is because the grease will come during cooking and washing and the paint will also gradually come off due to heating and will contaminate the food. Hence, galvanisation using zinc is the preferred option.
3. An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be
(a) Calcium
(b) Carbon
(c) Silicon
(d) Iron
Answer: (a) Calcium
Calcium reacts with oxygen to give the ionic compound Calcium oxide (CaO). Since CaO is an ionic compound it has high melting point. CaO is soluble in water to form calcium hydroxide (Ca(OH)2).
CaO + H2O —> Ca(OH)2
4. Food cans are coated with tin and not with zinc because
(a) Zinc is costlier than tin.
(b) Zinc has a higher melting point than tin.
(c) Zinc is more reactive than tin.
(d) Zinc is less reactive than tin.
Answer: (c) Zinc is more reactive than tin.
Food cans are coated with tin and not with zinc because zinc is higher in the reactivity series than tin and hence is more reactive than tin. If zinc is used then it might reacts with the food leading to food poisoning.
5. You are given a hammer, a battery, a bulb, wires and a switch.
(a) How could you use them to distinguish between samples of metals and non-metals?
(b) Assess the usefulness of these tests in distinguishing between metals and non-metals.
Answer:
(a) Metals are malleable, allowing them to be hammered into sheets, while non-metals are brittle and break easily, lacking malleability. Metals conduct electricity well, enabling a bulb to light up when connected with a battery, wire and switch. In contrast, non-metals are poor conductors of electricity and cannot light up a bulb under the same conditions.
(b) These tests are generally useful for distinguishing between metals and non-metals. However, there are exceptions. For instance, sodium and potassium, although metals, are not malleable and are quite brittle. Additionally, graphite, an allotrope of carbon and a non-metal, is a good conductor of electricity.
6. What are amphoteric oxides? Give two examples of amphoteric oxides.
Answer:
Metal oxides which react with both acids as well as bases to produce salts and water are known as amphoteric oxides. Teo examples are aluminium oxide (Al2O3) and lead oxide (PbO).
7. Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
Answer:
Two metals that will displace hydrogen from dilute acids are zinc and magnesium as they are high in the reactivity series and are hence reactive. Two metals that will not displace hydrogen from dilute acids are silver and gold as they are low in the reactivity series and are hence not reactive.
8. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
Answer:
In the electrolytic refining of a metal M, the impure metal M is taken as the anode, a thin strip of the pure metal is taken as the cathode and a solution of the metal salt is used as the electrolyte.
9. Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in figure below.
(a) What will be the action of gas on
(i) dry litmus paper?
(ii) moist litmus paper?
(b) Write a balanced chemical equation for the reaction taking place.
Answer:
(a) When sulphur powder is heated in air sulphur dioxide is formed.
(i) The gas will have no effect on dry litmus paper.
(ii) On contact with moist litmus paper, sulphur dioxide forms sulphurous acid (H2SO3) which turns blue litmus red.
(b) First reaction: S(s) + O2(g) —> SO2(g)
Second reaction: SO2(g) + H2O(l) —> H2SO3(aq)
10. State two ways to prevent the rusting of iron.
Answer:
Two ways to prevent the rusting of iron are:
(i) Painting the surface of iron.
(ii) Coating iron with a thin layer of zinc by the process of galvanisation.
11. What type of oxides are formed when non-metals combine with oxygen?
Answer:
Non-metals combine with oxygen form oxides which are either acidic or neutral for example NO2, SO2 etc.
12. Give reasons
(a) Platinum, gold and silver are used to make jewellery.
(b) Sodium, potassium and lithium are stored under oil.
(c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
Answer:
(a) Platinum, gold and silver are used to make jewellery.
Platinum, gold and silver are used to make jewellery because they are lustrous, malleable and ductile. Also, they are unreactive with oxygen, water etc and hence do not corrode.
(b) Sodium, potassium and lithium are stored under oil.
Sodium, potassium, and lithium are stored under oil to prevent them from reacting with moisture and oxygen in the air. These metals are highly reactive and can easily undergo oxidation or even ignite when exposed to air. Storing them under oil creates a barrier that isolates them from air and moisture, ensuring that they do not react and accidents do not occur.
(c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.
Aluminium is highly reactive, hence it forms a protective aluminium oxide layer on its surface that prevents further reaction. This makes it safe and durable for cooking utensils.
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
It is easier to obtain a metal from its oxide, as compared to its sulphides and carbonates. Hence, carbonate and sulphide ores are usually converted into oxides first during the process of extraction.
13. You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.
Answer:
Lemon or tamarind juice are acidic and dissolve the basic copper carbonate which is present on tarnished copper vessels. Hence, the vessels become clean again.
14. Differentiate between metal and non-metal on the basis of their chemical properties.
Answer:
| Metal | Non-metal |
| (i) Metals combine with oxygen to form basic oxides. | (i) Non-metals react with oxygen to form oxides which are acidic or neutral. |
| (ii) Metals react with dilute acids to form salt and hydrogen. | (ii) Non-metals do not react with acids. |
| (iii) Metals react with water to form metal hydroxides. | (iii) Non-metals do not react with water. |
15. A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?
Answer:
The solution used was Aqua regio which is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1. Aqua regia dissolves gold and platinum. In this case the cupper layer of the dull gold ornaments was dissolved by in aqua regia which reduced their weight but gave them the sparkling appearance.
16. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
Answer:
Copper is used to make hot water tanks and not steel because does not react with water or steam whereas iron reacts with steam to form ferric oxide, which results in corrosion of the tanks.
Solutions to All In-text Activities of NCERT Class 10 Science Chapter 3 Metals and Non-metals
1. Complete Activity 3.1 (Page 37).
- Take samples of iron, copper, aluminium and magnesium. Note the appearance of each sample.
- Clean the surface of each sample by rubbing them with sand paper and note their appearance again.
Answer:
2. Complete Activity 3.2 (Page 37).
- Take small pieces of iron, copper, aluminium, and magnesium. Try to cut these metals with a sharp knife and note your observations.
- Hold a piece of sodium metal with a pair of tongs. CAUTION: Always handle sodium metal with care. Dry it by pressing between the folds of a filter paper.
- Put it on a watch-glass and try to cut it with a knife.
- What do you observe?
Answer:
3. Complete Activity 3.3 (Page 38).
- Take pieces of iron, zinc, lead and copper.
- Place any one metal on a block of iron and strike it four or five times with a hammer. What do you observe?
- Repeat with other metals.
- Record the change in the shape of these metals.
Answer:
4. Complete Activity 3.4 (Page 38).
- List the metals whose wires you have seen in daily life.
Answer:
5. Complete Activity 3.5 (Page 38).
- Take an aluminium or copper wire. Clamp this wire on a stand, as shown in Fig. 3.1.
- Fix a pin to the free end of the wire using wax.
- Heat the wire with a spirit lamp, candle or a burner near the place where it is clamped.
- What do you observe after some time?
- Note your observations. Does the metal wire melt?
Answer:
6. Complete Activity 3.6 (Page 39).
- Set up an electric circuit as shown in Fig. 3.2.
- Place the metal to be tested in the circuit between terminals A and B as shown.
- Does the bulb glow? What does this indicate?
Answer:
7. Complete Activity 3.7 (Page 39).
- Collect samples of carbon (coal or graphite), sulphur and iodine.
- Carry out the Activities 3.1 to 3.4 and 3.6 with these non-metals and record your observations.
Answer:
8. Complete Activity 3.8 (Page 40).
- Take a magnesium ribbon and some sulphur powder.
- Burn the magnesium ribbon. Collect the ashes formed and dissolve them in water.
- Test the resultant solution with both red and blue litmus paper.
- Is the product formed on burning magnesium acidic or basic?
- Now burn sulphur powder. Place a test tube over the burning sulphur to collect the fumes produced.
- Add some water to the above test tube and shake.
- Test this solution with blue and red litmus paper.
- Is the product formed on burning sulphur acidic or basic?
- Can you write equations for these reactions
Answer:
9. Complete Activity 3.9 (Page 41).
CAUTION: The following activity needs the teacher’s assistance. It would be better if students wear eye protection.
- Hold any of the samples taken above with a pair of tongs and try burning over a flame. Repeat with the other metal samples.
- Collect the product if formed.
- Let the products and the metal surface cool down.
- Which metals burn easily?
- What flame colour did you observe when the metal burnt?
- How does the metal surface appear after burning?
- Arrange the metals in the decreasing order of their reactivity towards oxygen.
- Are the products soluble in water?
Answer:
10. Complete Activity 3.10 (Page 42).
CAUTION: This Activity needs the teacher’s assistance.
- Collect the samples of the same metals as in Activity 3.9.
- Put small pieces of the samples separately in beakers half-filled with cold water.
- Which metals reacted with cold water? Arrange them in the increasing order of their reactivity with cold water.
- Did any metal produce fire on water?
- Does any metal start floating after some time?
- Put the metals that did not react with cold water in beakers half-filled with hot water.
- For the metals that did not react with hot water, arrange the apparatus as shown in Fig. 3.3 and observe their reaction with steam.
- Which metals did not react even with steam?
- Arrange the metals in the decreasing order of reactivity with water.
Answer:
11. Complete Activity 3.11 (Page 44).
- Collect all the metal samples except sodium and potassium again. If the samples are tarnished, rub them clean with sand paper. CAUTION: Do not take sodium and potassium as they react vigorously even with cold water.
- Put the samples separately in test tubes containing dilute hydrochloric acid.
- Suspend thermometers in the test tubes, so that their bulbs are dipped in the acid.
- Observe the rate of formation of bubbles carefully.
- Which metals reacted vigorously with dilute hydrochloric acid?
- With which metal did you record the highest temperature?
- Arrange the metals in the decreasing order of reactivity with dilute acids
Answer:
12. Complete Activity 3.12 (Page 44).
- Take a clean wire of copper and an iron nail.
- Put the copper wire in a solution of iron sulphate and the iron nail in a solution of copper sulphate taken in test tubes (Fig. 3.4).
- Record your observations after 20 minutes.
- In which test tube did you find that a reaction has occurred?
- On what basis can you say that a reaction has actually taken place?
- Can you correlate your observations for the Activities 3.9, 3.10 and 3.11?
- Write a balanced chemical equation for the reaction that has taken place.
- Name the type of reaction.
Answer:
13. Complete Activity 3.13 (Page 48).
- Take samples of sodium chloride, potassium iodide, barium chloride or any other salt from the science laboratory.
- What is the physical state of these salts?
- Take a small amount of a sample on a metal spatula and heat directly on the flame (Fig. 3.7). Repeat with other samples.
- What did you observe? Did the samples impart any colour to the flame? Do these compounds melt?
- Try to dissolve the samples in water, petrol and kerosene. Are they soluble?
- Make a circuit as shown in Fig. 3.8 and insert the electrodes into a solution of one salt. What did you observe? Test the other salt samples too in this manner.
- What is your inference about the nature of these compounds?
Answer:
14. Complete Activity 3.14 (Page 53).
- 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 (Fig. 3.13).
Answer:
Extra Questions to Complement Solutions to NCERT Class 10 Science Chapter 3 Metals and Non-metals
Very Short Answer Type:
1. Which metal is the best conductor of heat?
Answer:
Silver.
2. Why are electric wires coated with PVC?
Answer:
PVC is an excellent insulator, which helps prevent electrical shocks.
3. Name two metals which melt easily.
Answer:
Gallium and caesium.
4. Name a liquid metal.
Answer:
Mercury.
5. Name a lustrous non-metal.
Answer:
Iodine.
6. Name a non-metal that can exist in different forms.
Answer:
Carbon.
7. Name a non-metal that can conduct electricity.
Answer:
Graphite.
8. Metal oxide reacts with both acids and bases to produce salts. What kind of an oxide is it?
Answer:
Amphoteric oxide.
9. Name two metals that catch fire if kept in the open.
Answer:
Sodium and potassium.
10. Why do noble gases show little chemical reactivity?
Answer:
They have a completely filled valence shell, so there is no tendency to lose or gain electrons to attain a stable octet.
11. Name a liquid non-metal.
Answer:
Bromine.
12. Silver articles kept in air become black after sometime. Why?
Answer:
Silver reacts with sulphur in air to form a black coating of silver sulphide.
13. How do the properties of iron change when it is alloyed with carbon (about 0.05%)?
Answer:
Iron becomes hard and strong.
14. What substances would you mix with iron to get stainless steel?
Answer:
Nickel and chromium.
15. What is an amalgam?
Answer:
An alloy is known as an amalgam if one of the metals is mercury.
Multiple Choice Questions (MCQ):
1. Which of the following is not an alkali metal?
(A) Lithium
(B) Sodium
(C) Potassium
(D) Iron
Answer: (D) Iron
2. Diamond and graphite are:
(A) Allotropes
(B) They are both hard substances
(C) They are both conductors of electricity
(D) They are both non-metals
Answer: (A) and (D)
3. Copper (II) oxide is a:
(A) Acidic oxide
(B) Basic oxide
(C) Neutral salt
(D) Forms when metallic copper is heated in air
Answer: (B) and (D)
Copper is a metal and hence copper oxide is a basic oxide. It forms when copper is burnt in air.
4. Which of the following metals does not react with water at all?
(A) Sodium
(B) Copper
(C) Magnesium
(D) Aluminium
Answer: (B) Copper
Copper does not react with hot water, cold, water or steam.
5. The composition of aqua-regia is
(A) Concentrated HCl: Concentrated HNO3 = 3: 1
(B) Concentrated HNO3: Concentrated HCl= 3: 1
(C) Concentrated HCl: Dilute HNO3 = 3: 1
(D) Dilute HCl: Concentrated HNO3 = 3: 1
Answer: (A) Concentrated HCl: Concentrated HNO3 = 3: 1
6. The following metals react with dilute hydrochloric acid: Mg, Al, Zn, Fe. Which metal will react the fastest?
(A) Mg
(B) Al
(C) Zn
(D) Fe
Answer: (A) Mg
The rate of formation of bubbles is fastest in case of magnesium indicating that magnesium is the most reactive.
7. Which of the following is true about sodium chloride?
(A) It exists as molecules
(B) It exists as aggregates of oppositely charged ions
(C) It has a low melting point
(D) It is soluble in petrol
Answer: (B)
Sodium chlorideexists as aggregates of oppositely charged ions, have high melting points and are insoluble in petrol and kerosene.
8. Which of the following is not an ionic compound?
(A) LiCl
(B) CaCl2
(C) CaO
(D) CO2
Answer: (D) CO2
9. Which of the following metals is found in a combined state as their sulphide or oxide ores?
(A) Au
(B) Ag
(C) Pt
(D) Cu
Answer: (D) Cu
Copper is found in the free state as well in the combined state.
10. Which of the following reactions is possible?
(A) Zn + CaSO4
(B) Ca + MgSO4
(C) Cu + FeSO4
(D) Al + MgSO4
Answer: (B) Ca + MgSO4
Calcium (Ca) is higher in the reactivity series than Magnesium (Mg). Hence, it displaces Mg from MgSO4 salt to form CaSO4. This reaction is called a displacement reaction.
Short Answer Type:
1. Name two metal oxides that dissolve in water. Give the corresponding reactions.
Answer:
Two metal oxides that dissolve in water are sodium oxide (Na2O) and potassium oxide (K2O). The reactions are shown below:
Na2O(s) + H2O(l) —> 2NaOH(aq)
K2O + + H2O(l) —> 2KOH(aq)
2. When a calcium sample is placed in water, it floats. Why?
Answer:
Calcium reacts with water to form calcium hydroxide (Ca(OH)2) and hydrogen gas.
Ca(s) + 2H2O —> Ca(OH)2(aq) + H2(g)
The bubbles of hydrogen gas sticks to the surface of calcium metal, thereby making it float.
3. Many metals react with dilute hydrochloric acid to evolve H2 gas. Why is H2 gas not evolved when a metal reacts with nitric acid?
Answer:
Nitric acid is a strong oxidising agent and so it oxidises the hydrogen produced to water and itself gets reduced to any of the nitrogen oxides such as N2O, NO and NO2.
4. How can you conclusively determine the reactivity series of metals?
Answer:
You can conclusively determine the reactivity series of metals by performing displacement reactions. The more reactive metal will displace the less reactive metal from its salt. Hence, the reactivity dries can be developed.
5. How would you extract mercury from cinnabar?
Answer:
Cinnabar (HgS) is a sulphide ore of mercury. Mercury lies low in the activity series and hence is very unreactive. Therefore, HgS can be reduced to mercury by heating alone. When HgS is heated is air it is first converted to mercuric oxide (HgO). On further heating, HgO is reduced to mercury. The reactions are shown below:
2HgS(s) + 3O2(g) + Heat —> 2HgO(s) + 2SO2(g)
2HgO(s) + Heat —> 2Hg(l) + O2(g)
6. Define roasting and calcination.
Answer:
Roasting is the process by which sulphide ores are converted into oxides by heating strongly in excess air. Calcination is the process by which carbonates are converted into oxides by heating strongly in limited air.
7. A metal carbonate A on heating gives an oxide B and a gas C which turns lime water milky. The same metal lies right above iron and right below aluminium in the activity series. Identify A, B and C by their formula. What is the reaction described here called?
Answer:
The metal which lies above iron and below aluminium in the activity series is zinc. Zinc carbonate (Zn(CO3)) on heating gives zinc oxide (ZnO) and carbon dioxide. Carbon dioxide turns lime water milky. The reaction is as follows:
ZnCO3(s) + Heat —> ZnO(s) + CO2(g)
Therefore, A is ZnCO3, B is ZnO and C is CO2.
The reaction described here is called calcination.
8. The galvanised article is protected against rusting even if the zinc coating is broken. Can you reason this out?
Answer:
Zind is more reactive than iron and hence even if the zinc coating is broken, the zinc still reacts with atmospheric oxygen to form a protective layer of zinc oxide. This zinc oxide layer protects the galvanised article from rusting.
9. Name the substance that gets reduced in thermit reaction and the substance that gets oxidised. Name the product which is present in the molten state and the product that is present in the solid state.
Answer:
Iron (III) oxide (Fe2O3) is reduced to iron and Aluminium (Al) is oxidised to aluminium oxide. The product that is present in molten state is metallic iron (Fe). The product that is present in the solid state is aluminium oxide (Al2O3).
10. What process is suitable for extraction of pure aluminium from aluminium oxide? Why cannot the process of reduction of aluminium oxide using carbon be used instead?
Answer:
Electrolytic reduction is suitable for extraction of pure aluminium from aluminium oxide. Aluminium is very reactive and has a stronger affinity for oxygen than carbon. Hence, carbon cannot reduce aluminium oxide to metallic aluminium.
11. The electrical conductivity and melting point of an alloy is less than that of pure metals. Give examples of both.
Answer:
Brass, an alloy of copper and zinc (Cu and Zn), and bronze, an alloy of copper and tin (Cu and Sn), are not good conductors of electricity whereas copper by itself is a good conductor of electricity. Solder, an alloy of lead and tin (Pb and Sn), has a lower melting point than both lead and tin.
Long Answer Type:
1. You are trying obtain pure magnesium from magnesium chloride (MgCl2) using electrolytic reduction.
(i) Give the reaction that occurs at the anode.
(ii) Give the reaction that occurs at the cathode.
(iii) The pure metal is deposited in which electrode?
(iv) Which gas is liberated in the process and at which electrode?
Answer:
(i) 2Cl– —> Cl2 + 2e–
(ii) Mg2+ + 2e– —> Mg
(iii) The pure metal is deposited at the cathode.
(iv) Chlorine gas is liberated at the anode.
2. You are given a sample of zinc that is still impure after extraction.
(i) What method would you use to purify impure zinc?
(ii) In the process used what would you take as the anode?
(iii) What would you take as the cathode?
(iv) What electrolyte would you use?
(v) Where is the pure metal collected?
Answer:
(i) The method of electrolytic refining is used.
(ii) The impure zinc is taken as the anode.
(iii) A thin strip of pure zinc is taken as the cathode.
(iv) A zinc sulphate solution is taken as the electrolyte.
(v) The pure metal is deposited at the cathode.
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Frequently Asked Questions (FAQs) on NCERT Solutions to Class 10 Science Chapter 3 Metals and Non-metals
In our solutions material for Chapter 3 you will find solutions to all in-text questions, exercise problems and in-text activities in one convenient place. We have also included amazing figures which will help you visualise the concepts. In addition to that, we have also included a set of extra questions to further help you prepare. Also, the free PDF solutions are available for download anytime!
The following topics are covered:
3.1 Physical Properties
– 3.1.1 Metals
– 3.1.2 Non-metals
3.2 Chemical Properties of Metals
– 3.2.1 What happens when Metals are burnt in air
– 3.2.2 What happens when Metals react with Water
– 3.2.3 What happens when Metals react with Acids
– 3.2.4 How do Metals react with Solutions of other Metals Salts
– 3.2.5 The Reactivity Series
3.3 How do Metals and Non-metals React
– 3.3.1 Properties of Ionic Compounds
3.4 Occurrence of Metals
– 3.4.1 Extraction of Metals
– 3.4.2 Enrichment of Ores
– 3.4.3 Extracting Metals Low in the Activity Series
– 3.4.4 Extracting Metals in the Middle of the Activity Series
– 3.4.5 Extracting Metals towards the Top of the Activity Series
– 3.4.6 Refining of Metals
3.5 Corrosion
-3.5.1 Prevention of Corrosion
Here are the number of questions for the chapter:
(i) 4 Multiple Choice Questions (1, 2, 3, 4)
(ii) 9 Short Answer Type Questions (5 – 11, 13 – 16)
(iii) 1 Long Answer Type Question (Question 12)
It is important that you study the reactions in this chapter in detail. Understand how they happen instead of just memorising. Study the formation of ionic compounds in detail and know how to draw the structures – this part is important for your exams. Also, study the section on extractive metallurgy well – you will see questions from this part in your exams. We have solved all activities for you, so study them well. Then you can test your knowledge using our extra problem set.
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