1Give 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 & Reference:
(i) Mercury
(ii) Sodium or Potassium
(iii) Silver
(iv) Lead or Mercury
(Section 3.1.1, Physical Properties of Metals)
2Explain the meanings of malleable and ductile.
Answer & Reference: Malleable: Metals can be beaten into thin sheets. Ductile: Metals can be drawn into thin wires.
(Section 3.1.1, Activities 3.3 and 3.4)
3Why is sodium kept immersed in kerosene oil?
Answer & Reference:
Sodium reacts so vigorously with oxygen and moisture in air that it catches fire. Hence, it is kept in kerosene oil to prevent accidental fires. (Section 3.2.1)
4Write equations for the reactions of (i) iron with steam (ii) calcium and potassium with water.
5Samples of four metals A, B, C and D were taken... (see full question in PDF)
Answer & Reference:
(i) Most reactive metal: B
(ii) B will displace copper from CuSO₄, so blue solution turns green and reddish-brown deposit appears.
(iii) Order of decreasing reactivity: B > A > C > D
(Based on Reactivity Series – Table 3.2, Section 3.2.5)
6Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H₂SO₄.
Answer & Reference:
Hydrogen gas (H₂) is produced.
Reaction: Fe(s) + H₂SO₄(aq) → FeSO₄(aq) + H₂(g)
(Section 3.2.3)
7What would you observe when zinc is added to a solution of iron(II) sulphate? Write the chemical reaction.
Answer & Reference:
Green colour of FeSO₄ fades and greyish deposit of iron forms.
Reaction: Zn(s) + FeSO₄(aq) → ZnSO₄(aq) + Fe(s)
(Section 3.2.4, Activity 3.12)
8(i) Write electron-dot structures for sodium, oxygen and magnesium. (ii) Show formation of Na₂O and MgO. (iii) What ions are present?
Answer & Reference:
(i) Na• , •O• , •Mg•
(ii) Na transfers 1 e⁻ to O → Na⁺ and O²⁻ → Na₂O
Mg transfers 2 e⁻ to O → Mg²⁺ and O²⁻ → MgO
(iii) Na₂O: Na⁺ and O²⁻; MgO: Mg²⁺ and O²⁻
(Section 3.3, Figures 3.5 and 3.6)
9Why do ionic compounds have high melting points?
Answer & Reference:
Due to strong electrostatic forces between oppositely charged ions, large energy is needed to break the bonds. (Section 3.3.1, Table 3.4)
10Define: (i) Mineral (ii) Ore (iii) Gangue
Answer & Reference:
(i) Mineral: Naturally occurring elements/compounds in earth’s crust.
(ii) Ore: Mineral with high metal % that can be profitably extracted.
(iii) Gangue: Impurities like soil/sand in ores.
(Section 3.4)
12What chemical process is used for obtaining a metal from its oxide?
Answer & Reference:
Reduction using carbon (for medium reactivity metals) or electrolysis (for high reactivity metals). (Sections 3.4.4 and 3.4.5)
13Which of the following pairs will give displacement reactions? (a) NaCl + Cu (b) MgCl₂ + Al (c) FeSO₄ + Ag (d) AgNO₃ + Cu
Answer & Reference:
Only (d) AgNO₃ + Cu → Cu(NO₃)₂ + Ag
Reason: Cu is more reactive than Ag (see Reactivity Series). (Section 3.2.5)
14Which method prevents rusting of iron frying pan? (a) grease (b) paint (c) zinc coating (d) all
Answer & Reference:
(c) Applying a coating of zinc (galvanisation) is suitable for cooking utensils; grease/paint would burn off. (Section 3.5.1)
15An element reacts with oxygen to give high-melting, water-soluble compound. Element is likely: (a) calcium (b) carbon (c) silicon (d) iron
Answer & Reference:
(a) Calcium → CaO → Ca(OH)₂ (soluble alkali, high melting). Non-metals like C/Si form acidic oxides insoluble in water. (Section 3.2.1)
16Food cans are coated with tin, not zinc because: (a) zinc costlier (b) higher m.p. (c) zinc more reactive (d) less reactive
Answer & Reference:
(c) Zinc is more reactive than tin and may react with food acids. (Reactivity Series: Zn > Sn)
17How to distinguish metals/non-metals using hammer, battery, bulb, wires, switch?
Answer & Reference:
Oxides that react with both acids and bases to form salt + water.
Examples: Aluminium oxide (Al₂O₃), Zinc oxide (ZnO). (Section 3.2.1)
19Name two metals that displace H₂ from dilute acids, and two that don’t.
Answer & Reference:
Displace H₂: Mg, Zn
Do not: Cu, Ag
(Metals above H in reactivity series displace H₂; below do not. Table 3.2)
20In electrolytic refining of metal M, what are anode, cathode, electrolyte?
Answer & Reference:
Anode: Impure metal M
Cathode: Thin strip of pure metal M
Electrolyte: Aqueous solution of salt of M
(Section 3.4.6, Fig. 3.12)
21Pratyush heated sulphur... (a) Action on dry/moist litmus? (b) Equation?
Answer & Reference:
(a) No effect on dry litmus; moist blue litmus turns red (acidic gas SO₂).
(b) S(s) + O₂(g) → SO₂(g)
(Section 3.1.2, Activity 3.8)
22State two ways to prevent rusting of iron.
Answer & Reference:
(i) Galvanisation (coating with zinc)
(ii) Painting or oiling
(Section 3.5.1)
23What type of oxides are formed when non-metals combine with oxygen?
Answer & Reference:
Acidic or neutral oxides (e.g., CO₂ acidic, CO neutral). (Section 3.1.2)
24Give reasons: (a) Au/Ag/Pt for jewellery (b) Na/K/Li stored under oil (c) Al used for utensils (d) carbonate/sulphide ores converted to oxides
Answer & Reference:
(a) Low reactivity, lustrous, do not corrode.
(b) Highly reactive with air/water → stored in oil.
(c) Forms protective oxide layer → corrosion resistant.
(d) Easier to reduce oxides to metals than sulphides/carbonates.
(Sections 3.2.1, 3.4.4)
25Why are lemon/tamarind used to clean tarnished copper vessels?
Answer & Reference:
Acid in lemon/tamarind neutralises basic copper carbonate (green layer) and dissolves it. (Section 3.5)
26Differentiate metals and non-metals based on chemical properties.
Answer & Reference:
Property
Metals
Non-Metals
Oxides
Basic (or amphoteric)
Acidic or neutral
Reaction with acids
Displace H₂ (if above H)
No H₂ displacement
Ion formation
Lose e⁻ → cations
Gain e⁻ → anions
Reaction with Cl₂
Form ionic chlorides
Form covalent chlorides
(Sections 3.2 and 3.3)
27Goldsmith reduced weight of bangles using a solution. What was it?
Answer & Reference:
Aqua regia (3:1 mix of conc. HCl and HNO₃), which dissolves gold. (Section 3.2.3)
28Why is copper used for hot water tanks, not steel?
Answer & Reference:
Iron (in steel) reacts with hot water/steam; copper does not react with water even at high temps. (Section 3.2.2)