Questions in text
Q1. 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 (Hg) is a liquid at room temperature.
(ii) Sodium (Na) or potassium (K) can be easily cut with a knife.
(iii) Silver (Ag) is the best conductor of heat.
(iv) Lead (Pb) or mercury (Hg) is a poor conductor of heat.
Q2. Explain the meanings of malleable and ductile.
Answer:
Malleable means the property of a metal to be beaten into thin sheets by hammering. Ductile means the property of a metal to be drawn into thin wires.
Q3. Why is sodium kept immersed in kerosene oil?
Answer:
Sodium is kept immersed in kerosene oil to protect it from reacting with moisture and oxygen in the air, as it reacts very vigorously with them and can catch fire.
Q4. Write equations for the reactions of (i) iron with steam (ii) calcium and potassium with water
Answer:
(i) Iron reacts with steam to form iron(II,III) oxide and hydrogen gas:
3Fe(s) + 4H2O(g) ? Fe3O4(s) + 4H2(g)
(ii) Calcium reacts with water to form calcium hydroxide and hydrogen:
Ca(s) + 2H2O(l) ? Ca(OH)2(aq) + H2(g)
Potassium reacts with water to form potassium hydroxide and hydrogen:
2K(s) + 2H2O(l) ? 2KOH(aq) + H2(g)
Q5. 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. 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) Metal B is the most reactive as it displaces iron from iron(II) sulphate and also displaces copper from copper(II) sulphate.
(ii) If B is added to a solution of copper(II) sulphate, a displacement reaction will occur. B will displace copper, so a brownish-red deposit of copper metal will be observed on B, and the blue colour of copper(II) sulphate solution will fade or change colour as B's salt is formed.
(iii) The order of decreasing reactivity is: B > A > C > D
Q6. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute HCl.
Answer:
Hydrogen gas (H2) is produced when dilute hydrochloric acid is added to a reactive metal.
The chemical reaction when iron reacts with dilute hydrochloric acid is:
Fe(s) + 2HCl(aq) ? FeCl2(aq) + H2(g)