Question 3
- (i) Name the gas produced in the set-up
(ii) State the function of each of the reagents A and B.
(iii) Suggest one substance each that could be used in place of A and B. - (i) I. State two possible properties of the gas.
II. State a physical property of the gas that would enable its diffusion to be detected easily.
(ii) Name the method of collection of the gas. Give a reason for the answer.
(iii) Name one other gas that could be collected by the same method - The table below shows the pH of solutions T to Z.
(i) Give the letters of the solutions which will turn:
I. blue litmus paper red;
II. red litmus paper blue.
(ii) Which of the solutions will give out carbon (IV) oxide rapidly when mixed with HCO3- and CO32-(aq) ions ?
(iii) Give the letter of one solution that will not change the colour of
I. methyl orange to yellow;
II. phenolphathalein to purple.
Observation
The question was popular among the candidates.
In part (a), majority of the candidates wrote formula of the gas produced, instead of name. Also, some candidates could not recognize the diagram.
In part (b), majority of the candidates named the method of collecting the gas, but could not give a reason for the answer.
In part (c), majority of the candidates were familiar with the pH table, and they could differentiate between acidic and basic solutions.
The expected answers include:
-
(i) Sulphur (IV) oxide
(ii) A is to dry the gas
B is to identify / test / confirm the gas produced
(iii) In place of A: CaCl2 / fused calcium chloride/silica gel - (i) I - Colourless gas
- Soluble in water
- Pungent / irritating/ choking smell
- can be easily liquidified
- Heavier/Denser than air
II - Odour of the gas / ( pungent / irritating / choking smell )
(ii) Downward delivery of gas / upward displacement of air Gas is denser / heavier than air
(iii) Chlorine, hydrogen sulphide, hydrogen chloride /carbon (IV) oxide /Nitrogen( IV) oxide - (i) I - T,U,V
II - X,Y,Z
(ii) V
(iii) I - W/T/U/V
II - W/T/U/V