The diagram below shows an experimental set-up. Use the diagram to answer questions 2(a) and 2(b).

(a)(i)       What is the aim of the experiment?                                             [1 mark]
    (ii)       What would be observed if air is blown into tube B and sucked out     of tube A? [2 marks]
   (iii)       Give reasons for the observation.                                               [3 marks]

(b)       List the components of expired air.                                                [4 marks]

OBSERVATION

This question was attempted by many candidates but candidates’ responses were not adequate. Most candidates were unable to state the aim of the experiment, what would be observed if air is blown into tube B and out of tube A. Candidates also missed the reasons for the observation.
Question 2(b) required candidates to list the components of expired air and many candidates responded correctly.
The expected answers are:
(a)(i) Aim
To compare the amount of carbon dioxide in exhaled air with the amount in the atmosphere.
Observation
(ii) - The lime water in B becomes milky; while the lime water in A remains clear.
(iii) The air flowing in to A is from the atmosphere. The air flowing into B is from the mouth/expired air; the expired air contains more carbon dioxide, which turns the lime water in B cloudy/milky.