Properties of the elements listed in question 2(a) were correctly interpreted by candidates as well as the products obtained when chlorine is passed into each of the solution of iron(II) chloride and potassium bromide. However, candidates could not give the correct observation of change of colour in the solutions.
The differences between conductors and electrolytes were poorly stated because candidates failed to use the appropriate technical terms.
Part (d) was a numerical question and this was poorly handled.
The expected answers are:
2(a) (i) nitrogen
(ii) potassium
(iii) aluminum
(iv) fluorine
(b) (i) I. green solution turns yellow/brown
II. colourless solution turns orange/brown
I. iron (III) chloride
II. bromide and potassium chloride
I. 2Fe2+(aq) + Cl2(g) 
2 Fe3+(aq) + 2Cl-(aq)
II. 2Br-(aq) + Cl2(g) 2Cl-(aq) + Br2
Redox reaction and redox/displacement reaction
| Conductors |
Electrolytes |
| Not decomposed by electric current |
decomposed by electric current |
| Are usually solids |
are aqueous solutions or molten salts |
| Free mobile electrons conduct current |
ions conduct electric current |
(differences must correspond to score)
(d) Molar mass of NH3 = 14 + 1 x 3 = 17 gmol-1
Molar mass of (NH4)2 SO4 = [(14 + 1 x 4) x 2 + 32 + 16 x 4)] = 132g mol-1
(2 x 17)g of NH3 = 132g (NH4)2SO4
34 = 132g
85g = 132 x 85
34
= 330g
OR
Molar mass of NH3 = 14 + 1 x 3 = 17g mol-1 Mass to mass relationship
Molar mass of (NH4)2 SO4 = [(14 + 1 x 4) x 2 + 32 + 16 x 4) = 132g mol-1
No. of moles of NH3 = 85 = moles
17
Since 2 moles of NH3 = mole (NH4)2 SO4
5moles= 1x5
= 2.5moles (NH4)2 SO4
Mass of (NH4)2 SO4 = 2.5 x 132
= 330g
