This is not a popular question among the candidates. The few that attempted it could not perform well because of Inconsistency in their readings as majority of the responding candidates did not record b0
the part (b) was poorly attempted as many could not define boiling point nor recall the effect of impurities on the determination of boiling point of a liquid.
The expected answers are:
- Value of b„ read and recorded in °C
- Five values of bi read and recorded in °C to 1d.p and in trend (Trend: As M increases, ij increases)
- Five values of M correctly recorded in gm
- Five values θ =(bi - bo) correctly evaluated to 1d.p
- Composite table showing bo, bi, Mi, and θ
Candidates are also expected to:
- Plot five points on graph – Distinguish betweenthe axes
-- Choose reasonable scales
-- Draw line of best fit -- -- Determine the slope of the graph
-- State any two of the following precaution in acceptable language.
- -- Avoided splashing of water
-- Avoided parallax error on thermometer/stopwatch/clock
- -- Avoided noted zero error on stop watch/clock
- -- Ensured thermometer did not touch the beaker.
- -- Repeated readings shown on the table
(b) (i) This is the temperature of a liquid at which the saturated vapour pressure of the liquid equals the external atmospheric pressure
- Impurities increase the boiling point of a liquid