Part (a) was well attempted. However some candidates mistook specific latent heat of fusion for latent heat of fusion.
The purpose of tube P was poorly identified indicating poor knowledge of experiment used for determining the specific latent heat of vaporization of water.
Part (b) was poorly attempted by majority of the responding candidates though many candidates recalled the fact that pure water boil at a temperature below 100oC when its s.v.p is lower than normal atmospheric pressure. However, majority of the candidates could not explain such using a round bottom flask. Some even attributed it to impurities rather than reduction in pressure.
Part (c) was well attempted by majority of the responding candidates.
Part (d) was fairly well attempted though some candidates used wrong formula.
The expected answers were as follows:
(a) (i) This is the amount of heat required to change a substance from the solid
state to the liquid state without a change in/at constant temperature.
(ii) It is to ensure that only dry steam is used.
(b) Pure water boils at a temperature below 100oC when its s.v.p is less than normal atmospheric pressure.
To achieve this:
- Fill a round bottom flask to ¾ of its volume.
- Insert a thermometer through the stopper and heat the flask to about 80oC.
- Invert the flask and place it under flowing tap water so as to reduce the pressure in the flask as a result of condensation of vapour.
(c) θ = Re - Ro
100 R100 - Ro
θ = 10.2 - 9.6 x 100
12.1 - 9.6
= 0.6 x 100
= 24. 0o C
- Heat lost by hot body = Heat gained by ice
MbCb Δθ = MiLf
2 x 2200 x (100 – 0) = Mi x 330000
Mi = 2 x 2200 x 100 = 4/3
= 1.33 kg.