A. (i) Electron affinity [1 mark]
(ii) Mole [1 mark]
B. Ammonium hydroxide when added to copper sulphate drop-wise forms a pale blue precipitate of copper hydroxide which dissolves in excess of ammonium hydroxide to form a deep blue solution.
[1 mark]
Sodium hydroxide when added to copper sulphate drop-wise forms a pale blue precipiate which is insoluble in excess sodium hydroxide. [1 mark]
C. (i) Ionic compounds have high melting points because there is a strong electrostatic force of attraction between the oppositely charged ions and hence a large amount of energy is required to break the strong bonding force between ions. [1 mark]
(ii) During the electrolysis of copper sulphate using platinum electrodes copper ions from copper sulphate solution get reduced on the platinum electrode. Cu2+(aq) + 2e− → Cu (s).
The blue colour of copper ions fades due to a decrease in Cu2+ ions and finally, the solution becomes colourless as soon as Cu2+ ions are exhausted. [1 mark]
(iii) Acetic acid is weak electrolyte which dissociates partially whereas HCl is strong electrolyte which dissociates completely. Therefore, conductivity of dilute hydrochloric acid is greater than acetic acid. [1 mark]
D. (i) At STP, 22.4 L or 22400 cc of any gas contain Avogadro number of molecules.
Here, the volumes of the gases are in the order of SO2 < N2 < O2. So the required arrangement of molecules in the increasing order is SO2 < N2 < O2. [1 mark]
(ii) In the electrochemical series of metals, the lower a metal is placed in the series, the easier is for it to get discharged at the cathode.
Among K+, Al3+, Cu2+, Cu2+
lies below Al3+ which in turn lies below K+ in the electrochemical series.
So the required order is Cu2+ < Al3+ < K+. [1 mark]
(iii) We know that atomic size increases from right to left and from top to bottom in the periodic table. So the required correct order of atomic radius is Li < Na < K. [1 mark]