Metals and Non-metals - NCERT Solutions

Questions from Text

Exercise Questions

Key Concepts

Questions from the Chapter

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.

(i) Mercury (Hg)

(ii) Sodium (Na) and Potassium (K)

(iii) Silver (Ag)

(iv) Lead (Pb) and Mercury (Hg)

2. Explain the meanings of malleable and ductile.

Malleable: Metals can be beaten into thin sheets. This property is called malleability. Gold and silver are the most malleable metals.

Ductile: Metals can be drawn into thin wires. This property is called ductility. Gold is the most ductile metal.

3. Why is sodium kept immersed in kerosene oil?

Sodium is a highly reactive metal that reacts vigorously with oxygen and water. If kept in open air, it can catch fire. To protect it from accidental fires and prevent reaction with air and moisture, sodium is kept immersed in kerosene oil.

4. Write equations for the reactions of (i) iron with steam (ii) calcium and potassium with water

(i) Iron with steam: 3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)

(ii) Calcium with water: Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)

Potassium with water: 2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g) + heat energy

5. 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	No reaction	No reaction
B	Displacement	No reaction	No reaction	Displacement
C	No reaction	No reaction	No reaction	No reaction
D	No reaction	No reaction	Displacement	Displacement

(i) Which is the most reactive metal? Metal B

(ii) What would you observe if B is added to a solution of Copper(II) sulphate? No reaction occurs

(iii) Arrange the metals A, B, C and D in the order of decreasing reactivity: B > A > D > C

6. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H₂SO₄.

Hydrogen gas is produced when dilute hydrochloric acid is added to a reactive metal.

Reaction of iron with dilute H₂SO₄: Fe(s) + H₂SO₄(aq) → FeSO₄(aq) + H₂(g)

7. What would you observe when zinc is added to a solution of iron(II) sulphate? Write the chemical reaction that takes place.

Zinc is more reactive than iron, so it displaces iron from iron(II) sulphate solution. The green color of iron(II) sulphate solution fades, and a grayish coating of iron is deposited on the zinc.

Chemical reaction: Zn(s) + FeSO₄(aq) → ZnSO₄(aq) + Fe(s)

8. (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?

(i) Electron-dot structures:

Sodium (Na): Na• (1 valence electron)
Oxygen (O): :Ö: (6 valence electrons)
Magnesium (Mg): Mg: (2 valence electrons)

(ii) Formation of Na₂O: 2Na + ½O₂ → Na₂O (2Na atoms transfer 1 electron each to O atom)

Formation of MgO: Mg + ½O₂ → MgO (Mg atom transfers 2 electrons to O atom)

(iii) Ions present: In Na₂O - Na⁺ and O²⁻ ions; In MgO - Mg²⁺ and O²⁻ ions

9. Why do ionic compounds have high melting points?

Ionic compounds have high melting points because a considerable amount of energy is required to break the strong inter-ionic attraction between the positively and negatively charged ions in the crystal lattice.

10. Define the following terms. (i) Mineral (ii) Ore (iii) Gangue

(i) Mineral: The elements or compounds, which occur naturally in the earth's crust.

(ii) Ore: Minerals that contain a very high percentage of a particular metal and the metal can be profitably extracted from it.

(iii) Gangue: The impurities such as soil, sand, etc., that are present in an ore.

11. Name two metals which are found in nature in the free state.

Gold (Au) and Silver (Ag) are found in nature in the free state.

12. What chemical process is used for obtaining a metal from its oxide?

Reduction process is used for obtaining a metal from its oxide. The method depends on the reactivity of the metal:

For metals low in activity series: Heating alone
For metals in the middle of activity series: Reduction using carbon
For metals high in activity series: Electrolytic reduction

Exercise Questions

1. Which of the following pairs will give displacement reactions?

(a) NaCl solution and copper metal - No reaction (Copper is less reactive than sodium)

(b) MgCl₂ solution and aluminium metal - No reaction (Aluminium is less reactive than magnesium)

(d) AgNO₃ solution and copper metal - Displacement reaction occurs (Copper is more reactive than silver)

2. Which of the following methods is suitable for preventing an iron frying pan from rusting?

(d) All of the above.

Applying grease, paint, or a coating of zinc (galvanizing) are all effective methods to prevent rusting of iron.

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

Calcium reacts with oxygen to form calcium oxide (CaO), which has a high melting point and is soluble in water to form calcium hydroxide.

4. Food cans are coated with tin and not with zinc because

Zinc is more reactive and may react with acidic food contents, while tin is less reactive and safer for food containers.

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?

Using the hammer: Metals are malleable (can be beaten into sheets), while non-metals are brittle (break into pieces).
Using the battery, bulb, wires and switch: Set up an electric circuit. Metals conduct electricity (bulb glows), while non-metals (except graphite) do not conduct electricity (bulb does not glow).

(b) These tests are useful in distinguishing between metals and non-metals as they test fundamental properties: malleability and electrical conductivity.

6. What are amphoteric oxides? Give two examples of amphoteric oxides.

Amphoteric oxides are metal oxides that show both acidic and basic behavior. They react with both acids and bases to produce salts and water.

Examples: Aluminium oxide (Al₂O₃) and Zinc oxide (ZnO)

7. Name two metals which will displace hydrogen from dilute acids, and two metals which will not.

Metals that displace hydrogen from dilute acids: Zinc (Zn) and Iron (Fe)

Metals that do not displace hydrogen from dilute acids: Copper (Cu) and Silver (Ag)

8. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?

In electrolytic refining:

Anode: Impure metal M
Cathode: Thin strip of pure metal M
Electrolyte: Solution of salt of metal M

9. Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it.

(a) Action of gas on:

(i) dry litmus paper: No change
(ii) moist litmus paper: Turns red (acidic)

(b) Balanced chemical equation: S(s) + O₂(g) → SO₂(g)

10. State two ways to prevent the rusting of iron.

(1) Galvanization: Coating iron with a thin layer of zinc

(2) Painting: Applying a protective paint layer on iron surface

11. What type of oxides are formed when non-metals combine with oxygen?

Non-metals form acidic or neutral oxides when they combine with oxygen.

Examples: Carbon dioxide (CO₂ - acidic), Sulphur dioxide (SO₂ - acidic), Nitrous oxide (N₂O - neutral)

12. Give reasons

(a) Platinum, gold and silver are used to make jewellery.

These metals are lustrous, malleable, ductile, and do not corrode easily.

(b) Sodium, potassium and lithium are stored under oil.

These metals are highly reactive and can catch fire when exposed to air. Storing under oil prevents their reaction with oxygen and moisture.

Aluminium forms a protective oxide layer (Al₂O₃) that prevents further reaction. It is also a good conductor of heat.

(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 compared to its sulphides and carbonates.

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.

Copper vessels get tarnished due to the formation of basic copper carbonate. Lemon or tamarind juice contains acids (citric acid, tartaric acid) that react with the basic copper carbonate to form soluble salts, thus cleaning the vessels.

14. Differentiate between metal and non-metal on the basis of their chemical properties.

Property	Metals	Non-metals
Reaction with oxygen	Form basic oxides	Form acidic or neutral oxides
Reaction with water	React to form metal oxide/hydroxide and H₂	Generally do not react
Reaction with acids	Displace H₂ from dilute acids	Do not displace H₂
Reaction with bases	Generally do not react	Some react to form salts
Displacement reactions	More reactive displace less reactive	More reactive displace less reactive

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?

The man used aqua regia, a mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1. Aqua regia can dissolve gold, which is why the weight of the bangles reduced drastically.

16. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).

Copper does not react with water or steam, while iron (in steel) reacts with steam to form iron oxide and gets corroded. Copper is also a better conductor of heat than steel.

Key Concepts

Physical Properties of Metals

Metallic lustre (shining surface)
Generally hard (hardness varies)
Malleable (can be beaten into thin sheets)
Ductile (can be drawn into thin wires)
Good conductors of heat and electricity
Sonorous (produce sound when struck)
Generally solids at room temperature (except mercury)

Physical Properties of Non-metals

Generally dull (except iodine and graphite)
Generally soft (except diamond)
Not malleable or ductile
Poor conductors of heat and electricity (except graphite)
Not sonorous
Can be solids, liquids or gases at room temperature

Chemical Properties of Metals

React with oxygen to form basic oxides (some amphoteric)
React with water to form metal oxide/hydroxide and hydrogen
React with acids to form salt and hydrogen
More reactive metals displace less reactive metals from their compounds

Reactivity Series

Metal	Symbol	Reactivity
Potassium	K	Most reactive
Sodium	Na
Calcium	Ca
Magnesium	Mg
Aluminium	Al
Zinc	Zn	Reactivity decreases
Iron	Fe
Lead	Pb
[Hydrogen]	[H]
Copper	Cu	Least reactive
Mercury	Hg
Silver	Ag
Gold	Au

Formation of Ionic Compounds

Formed by transfer of electrons from metal to non-metal
Contain positively charged cations and negatively charged anions
Have high melting and boiling points
Generally soluble in water but insoluble in organic solvents
Conduct electricity in molten state or in aqueous solution

Extraction of Metals

Metals low in activity series (Cu, Ag, Au): Found in native state, extracted by heating alone
Metals in middle of activity series (Zn, Fe, Pb): Found as oxides, sulphides or carbonates, extracted by reduction with carbon
Metals high in activity series (K, Na, Ca, Mg, Al): Never found free, extracted by electrolytic reduction

Corrosion and Prevention

Corrosion: Deterioration of metals when exposed to air and moisture
Examples: Rusting of iron, tarnishing of silver, green coating on copper
Prevention: Painting, oiling, greasing, galvanizing, alloying, anodizing

Alloys

Homogeneous mixtures of two or more metals, or a metal and a non-metal
Have properties different from constituent metals
Examples: Steel (Fe+C), Brass (Cu+Zn), Bronze (Cu+Sn), Solder (Pb+Sn)