Physics Paper 1, May/June 2012  
Questions: 1 2 3 Main
General Comments

Question 2B



You are provided with a beaker, a thermometer, a stirrer, stop watch/clock, measuring cylinder, table salt, water and other necessary materials.

  1. Measure 200 cm3 of water into the beaker.
  2. Heat the water until it boils steadily for about 2 minutes
  3. Read and record the boiling point b0
  4. Add table salt of mass M = 10.0 g to the boiling water and stir continuously until another boiling point b| is attained
  5. Read and record bi
  6. Evaluate 0 = . (bi -b0)
  7. Using the same mixture, repeat the procedure four more times by adding 10.0 g of salt each time to give the cumulative mass Mj of salt as 20 g' 30 g' 40 g and 50g.
  8. In each case allow the mixture to boil steadily for at least 2 minutes then read    and
    record the boiling point bi
  9. Tabulate your readings
  10. Plot a graph with M| on the vertical axis and 0{ on the horizontal axis
  11. Determine the slope, s, of the graph.
  12. State two precautions taken to ensure accurate results

(b)       (i) Define the boiling point of a liquid.
           (ii)What effect does impurities have on the boiling point of a liquid?


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
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