Quiet a large number of the candidates could not describe how to identify the given solutions which required application of practical works.
The reasons for increasing boiling points in the given compounds were not correctly stated by most candidates.
A fair attempt was made at identifying gases based on their properties.
A good attempt was also made at comparing silicon and sulphur based on their properties.
This question was well attempted by majority of the responding candidates.
The expected answers are:
Test |
Observation |
Inference |
Aqueous solution of (NH4)2 CO3
+ dil HCL/HNO3/H2SO4 |
Brisk effervescene. Colourless gas turns lime water milky |
CO2 from CO32- |
NH4CL + AgNO2(aq) + dil HNO3 |
White precipitate insoluble in excess HNO3 |
Cl- present |
To each of the solutions add dil HCl/HNO3/H2SO4
Brisk effervescence; (NH4)2CO3 confirmed
No reaction; CL- confirmed.
And is therefore ammonium chloride.
(b) CO2; CS2, NaF
Increasing order of boiling point
CO2; weak van der Waal’s forces due to large size
NaF; ionic forces
Ionic forces stronger than van der Waal’s forces
(c) (i) NO2, CO2, HCl, Cl2, SO2, SO3, etc.
(ii) NH3, HCl
(iii) SO2 H2S
Silicon |
Sulphur |
A metalloid |
Non-metal |
A Solid |
A solid |
Semi conductor/conducts |
Non-conductor of electricity |
(They must correspond to score)
(e) Volume of sodium = 1 x b x h
= 3 x 4 x 10
= 120 cm3
Mass = Density x Volume
= 0.971 x 120 = 116.52g
23g of Na contains 6.02 x 1023 atoms
116.52g of Na = 116.52 x 6.02 x 1023
23
= 3.05 x 1024 atoms