NCERT Solutions for Class 10 Science Chapter 3 Metals and Non-Metals

NCERT Intext Questions

 Page Number 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.
  • Ans. (i) Mercury
  • (ii) Sodium
  • (iii) Silver
  • (iv) Lead
2. Explain the meanings of malleable and ductile.
Ans. Malleable: It is the property of a metal by which metal is converted into thin sheets without breaking when beaten or hammered. Ductile: It is a property of metal by which metal can be drawn into thin wires.
 Page Number 46
1. Why is sodium kept immersed in kerosene oil ?
Ans. Sodium is a very reactive metal and when it comes into the contact of O2, CO2 and H2O present in air, it gets vigorous and catches fire. Thus it is kept immersed in the kerosene to avoid the accidental fire.
2. Write equations for the reactions of:
(i) iron with steam,
(ii) calcium and potassium with water.

Ans. $$\text{(i)}\space 3Fe(s) + \underset{\text{Steam}}{4H_2O(g)} → \underset{\text{Iron (II, III) oxide}}{Fe_3O_4(s)} + 4H_2(g) \\ \text{(ii)}\space Ca(s) + 2H_2O(l) → \underset{\text{Calcium hydroxide}}{Ca(OH)_2(aq)} + H_2(g) \\ \space 2K(s) + \underset{\text{Cold}}{2H_2O(l)} → \underset{\text{Potassium hydroxide}}{2KOH(aq)} + H_2(g)+ \text{Heat}$$

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.
Ans. (i) B is the most reactive metal because it gives displacement reaction with iron (II) sulphate.
(ii) When metal B is added to copper (II) sulphate solution, a displacement reaction will take place due to which the blue colour of copper (II) sulphate solution will fade and a red-brown deposit of copper will be formed on metal B.
(iii) Metal B is the most reactive because it displaces iron from its salt solution. Metal A is less reactive because it displaces copper from its salt solution. Metal C is still less reactive because it can displace only silver from its salt solution and metal D is the least reactive because it cannot displace any metal from its salt solution. Hence, the decreasing order of reactivity of the metals is B > A > C > D.
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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.
Ans. Hydrogen gas is produced when dilute hydrochloric acid is added to a reactive metal. Chemical reaction 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.
Ans. When zinc is added to solution of iron (II) sulphate, zinc displaces iron and forms ZnSO4. A grey precipitate of iron is formed leaving behind a colourless solution of ZnSO4. This is because Zn is more reactive than iron.
$$\underset{\text{Iron (II) Sulphate (Greenish solution)}}{FeSO_4(aq)} + \underset{\text{Zinc}}{Zn(s)} → \underset{\text{Zinc sulphate (Colourless solution)}}{ZnSO_4(aq)} + \underset{Iron}{Fe(s)}$$
 Page Number 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 ions present in these compounds?
Ans. (i)
Element Sodium (Na) Oxygen (O) Magnesium (Mg)
Electron dot structure $$\underset{\text{2,8,1}}{\text{\.{Na}}}$$ $$\underset{\text{2,8,6}}{\underset{\text{\" }}{\cdot \text{\"{O}}\cdot}}$$ $$\underset{\text{2, 8, 2}}{\ddot Mg}$$
(ii) Formation of Na2O and MgO
(iii) In Na2O, ions present are Na+ (cation) and O2– (anion).
In MgO, ions present are Mg2+ (cation) and O2– (anion).
2. Why do ionic compounds have high melting points ?
Ans. The ionic compounds have high melting point because the ions present in it i.e., cation (+ve charge) and anion (–ve charge) are bound with strong electrostatic force of attraction. So to break it, high energy or heat is required. Due to this ionic compounds have high melting points.

 Page Number 53

1. Define the following terms:
(i) Mineral
(ii) Ore and
(iii) Gangue
Ans. (i) Mineral: The elements or compounds, which occur naturally in the earth’s crust, are known as minerals.
(ii) Ore: The mineral from which metal can be profitably extracted is called an ore.
(iii) Gangue: Ores mined from the earth are usually contaminated with large amounts of impurities such as soil, sand, etc. These impurities are called as gangue.
2. Name two metals which are found in nature in the free state.
Ans. Gold and platinum or copper and silver.
3. What chemical process is used for obtaining a metal from its oxide?
Ans. Metal can be extracted from its oxide by reduction process. In reduction process, the oxides of metal are reduced by reducing agents such as carbon at very high temperature to obtain its metal.
$$\text{Example: } \underset{\text{Zinc oxide}}{ZnO(s)} + \underset{\text{Carbon}}{C(s)} → \underset{\text{Zinc}}{Zn(s)} + \underset{\text{Carbon monoxide}}{CO(g)}$$

In this reaction zinc oxide is reduced by carbon on heating at high temperature to get zinc metal.

 Page Number 55

1. Metallic oxides of zinc, magnesium and copper were heated with the following metals:
Metal Zinc Magnesium Copper
1. Zinc oxide
2. Magnesium oxide
3. Copper oxide
In which cases will you find displacement reactions taking place?
Ans. A more reactive metal can displace a less reactive metal from its oxide. But out of zinc, magnesium, and copper metals, magnesium is the most reactive, zinc is less reactive whereas copper is the least reactive metal.
The displacement will take place in the following cases:
Metal Zinc Magnesium Copper
1. Zinc oxide - Displacement -
2. Magnesium oxide - - -
3. Copper oxide Displacement Displacement -
2. Which metals do not corrode easily?
Ans. Gold and Platinum, do not corrode easily because they do not loose electrons easily.
3. What are alloys?
Ans. An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal. For example, bronze is an alloy of copper and tin.

NCERT Exercise Questions

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
Ans. (d) AgNO3 solution and copper metal
Explanation: In displacement reaction highly reactive metal displaces less reactive metal.
Cu is less reactive than Na so it cannot displace Na.
Al is less reactive than Mg so it cannot displace Mg.
Ag is less reactive than Fe so it cannot displace Fe.
Cu is more reactive than Ag so it will displace Ag and form CuNO3.
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 the above
Ans. (c) Applying a coating of zinc
Explanation: We can prevent iron getting rusted by applying a coat of zinc or a thin coat of plastic helps to prevent rust. The process for coating metal like iron or steel with a thin zinc layer is known as galvanization.

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

Ans. (a) Calcium.
Explanation: Ca reacts with oxygen to form CaO which has high melting point and is soluble in water.
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 less reactive than tin
(d) zinc is more reactive than tin.
Ans. (d) zinc is more reactive than tin.
Explanation: Food cans are coated with tin and not with zinc because zinc is more reactive than tin and it may react with preserved food items.
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.
Ans. (a) We can easily dintinguish between metals and non-metals in a sample by comparing their properties.
Metals are malleable in nature i.e., when beaten with hammer it will be converted into thin sheets without breaking whereas non-metals are non-malleable i.e., brittle i.e., when beaten with hammer it will break into pieces.
Metals are good conductor of electricity because of presence of free electrons whereas non-metals are not good conductor of electricity. So, when metals are connected into circuit using battery bulb, wire and switch, current passes through the circuit and the bulb glows and when the non-metals are connected in circuit, bulb does not glow.
(b) Useful of these tests is because of malleability, metals can be casted into sheets. Metals are good conductors of electricity so these can be used for manufacturing electrical cables.
6. What are amphoteric oxides? Give two examples of amphoteric oxides?
Ans. Those metal oxides which show basic as well as acidic behaviour are known as amphoteric oxides. In other words, metal oxides that react wtih both acids and bases to form salt and water are called amphoteric oxides. Aluminium oxide and zinc oxide are amphoteric in nature.
$$\text{(a)}\space \underset{\text{Aluminium oxide}}{Al_2O_3(s)} + \underset{\text{Hydrochloric acid}}{6HCl(aq)} → \underset{\text{Aluminium chloride}}{2AlCl_3(aq)} + \underset{\text{Water}}{3H_2O(l)} \\ \underset{\text{Aluminium oxide}}{Al_2O_3(s)} + \underset{\text{Sodium hydroxide}}{2NaOH (aq)} → \underset{\text{Sodium aluminate}}{2NaAlO_2(aq)} + \underset{\text{Water}}{H_2O(l)}\\ \text{(b)}\space \underset{\text{Zinc oxide}}{ZnO} + \underset{\text{Hydrochloric acid}}{2HCl} → \underset{\text{Zinc chloride}}{ZnCl_2} + \underset{\text{Water}}{H_2O} \\ \underset{\text{Zinc oxide}}{ZnO} + \underset{\text{Sodium hydroxide}}{2NaOH} → \underset{\text{Sodium zincate}}{Na_2ZnO_2} + \underset{\text{Water}}{H_2O}$$
7. Name two metals which will displace hydrogen from dilute acids and two metals which will not.
Ans. (i) Metals which are more reactive than hydrogen can displace hydrogen from dilute acids.
Examples: Sodium and Potassium
(ii) Metals which are less reactise than hydrogen cannot displace hydrogen from dilute acids.
Example: Copper or silver.
8. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
Ans. (i) Cathode – Pure metal
(ii) Anode – Impure metal
(iii) Electrolyte – Metal salt solution
During electrolytic refining of a metal, impure metal is used as anode and a pure metal is used as cathode and metal salt solution is used as 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 the figure.
(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.
Ans. (a) During this experiment sulphur reacts with oxygen present in air and forms sulphur dioxide gas.
(i) There will be no action on dry litmus paper as both litmus paper and gas lack moisture (H2O).
(ii) The colour of moist litmus paper will turn red because when SO2 gas reacts with moisture (H2O), it will form H2SO4 which is an acid.
(b) Balanced chemical equation: $$\underset{\text{Sulphur}}{S} + \underset{\text{Oxygen}}{O_2} → \underset{\text{Sulphur dioxide}}{SO_2}$$
10. State two ways to prevent the rusting of iron.
Ans. By applying protective layer of paint on iron, a process called painting and a layer of zinc on iron, the process called galvanization, are the ways to prevent rusting of iron.
11. What type of oxides are formed when non-metals combine with oxygen?
Ans. Acid oxides and neutral oxides are formed when non-metals combine with oxygen. Acidic oxide as sulphur dioxide $$\underset{\text{Sulphur}}{S} + \underset{\text{Oxygen}}{O_2} → \underset{\text{Sulphur dioxide (Acidic)}}{SO_2} \\ \text{Neutral oxide as water} \\ \underset{\text{Hydrogen}}{2H_2 (g)} + \underset{\text{Oxygen}}{O_2 (g)} → \underset{\text{Water (Neutral)}}{H_2O_2 (l)}$$
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 reactiv e 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.
Ans. (a) Platinum, gold and silver are used to make jewellery because these are malleable and ductile. These are highly resistant to corrosion.
(b) Sodium, potassium and lithium are very reactive and catch fire when exposed to air. This is due to their low ignition temperature and high reactivity.
(c) Aluminium forms a non-reactive layer of aluminium oxide on its surface. This layer prevents aluminium to react with other substances. That is why aluminium is used to make cooking utensils.
(d) It is easier to reduce a metal oxide into free metal. Since it is easier to obtain metals from their oxides than from their carbonates or sulphides directly, therefore, the carbonate and sulphide ores are first converted to oxides for extracting the metals.

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.

Ans. The acids present in lemon or taramind juice reacts with coating of basic copper carbonate or copper oxide, neutralizing it, thus dissolving the layer; results in copper vessels loosing their brown surface.
14. Differentiate between metal and non-metal based on their chemical properties.
Metal Non-metals
(i) Metals react with oxygen to form basic oxides.
4NO + O2 → 2Na2O
Non-metals react with oxygen to form acidic or neutral oxide.
C + O2 → CO2
(ii) Metals react with water to form hydroxide and hydrogen.
2Na + H2O → 2NaOH + H2
Generally non-metals do not react with water.
(iii) Metals are electropositive. Non-metals are electronegative.
(iv) Metals displace hydrogen from dilute acid and form salts. Non-metals do not displaces hydrogen from dilute acid.
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 repeat. Can you play the detective to find out the nature of the solution he has used ?
Ans. The dishonest goldsmith dipped the gold bangles in aqua-regia (which contains 1 part of concentrated nitric acid and 3 parts of concentrated hydrochloric acid, by volume). Aqua-regia dissolves a considerable amount of gold from gold bangles and hence reduces their weight drastically. The dishonest goldsmith can recover the dissolved gold from aqua-regia by a suitable treatment.
16. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
Ans. Copper is used to make hot water tanks and not steel because:
(i) Copper does not react with water whereas steel reacts with water easily and thus corrodes.
(ii) Copper is unaffected by change in temperature whereas steel is influenced by steam.