(Question 3
(a) (i) What is an acid-base indicator?
(ii) When is an indicator said to be most suitable for an acid-bas titration?
(iii) Consider the acid-base titration reaction represented by the following equation:
NaOH(aq) + CH3COOH(aq) CH3COONa(aq) + H2O(l)
I. Name a suitable indicator for the reaction.
II. Explain briefly your answer in 3(a)(ii) I.
(b) (i) Write the ionic equation for the reaction between zinc and silver trioxonitrate (V)
solution.
(ii) Which type of reaction occurs between zinc and silver trioxonitrate (V) solution?
Give a reason for your answer.
(c) (i) Consider the reaction represented by the following equation:
CaCO3(s) + 2HCl(aq) CaCl2(aq) + CO2(g) + H2O(l).
State three factors that could increase the rate of the reaction.
- Explain briefly the observation that increase in temperature generally
increases the rate of reaction.
- (i) What is solubility?
(ii) Distinguish between saturated solution and unsaturated solution.
- A saturated solution of volume 10 cm3 yielded 0.06 g of its dry salt at 25oC.
Calculate the solubility of the salt in gdm-3.
This question was fairly attempted by candidates. In (a), candidates were unable to correctly define an acid-base indicator and were unable to explain the suitability of an indicator for a particular acid-base titration. Some candidates used colour in acid and base as a bases for defining indicators instead of changes in pH.
In (b), a majority of the candidates could not write ionic equations although a few of them could identify the reaction as displacement/redox.
In (c), most candidates gave general factors instead of being specific e.g. “concentration” instead of “increase in concentration of HCl” “surface area.” instead of surface area of CaCO3”.
In (d), candidates did not give the correct/complete definition of solubility. In defining solubility, some candidates lost marks for writing “in 1dm3 of solution” instead in 1 dm3 or solvent.
