Achievement Test 1 (Question 3 – 5) – Chemistry Form 5 Chapter 1 (Redox Equilibrium)

Question 3:
Figure 1 shows the set-up of apparatus and observation for the experiment to study displacement of a metal from its salt solution.


(a) Suggest a suitable X(NO₃)₂ solution and name the brown solid at the bottom of the test tube.

(b) Write the half equations for oxidation and reduction.

(c) Write the ionic equation for the redox reaction that takes place.

(d) State the change in oxidation number of X in this experiment.


Answer:
(a) Copper(II) nitrate solution.
  Copper

(b)
$$\text { Oxidation half equation : } \mathrm{Pb} \rightarrow \mathrm{~Pb}^{2+}+2 \mathrm{e}^{-}$$
$$\text { Reduction half equation : } \mathrm{Cu}^{2+}+2 \mathrm{e}^{-} \rightarrow \mathrm{Cu}$$

(c) $$\mathrm{Pb}+\mathrm{Cu}^{2+} \rightarrow \mathrm{Pb}^{2+}+\mathrm{Cu}$$

(d) +2 to 0

Question 4:
Table 1 shows the results of an experiment to study the displacement of halogen from its halide solution.


(a) Name the halogen gas that is passed into the test tube in this experiment.

(b) Name the product of the reaction that can be detected with dichloromethane, CH₂Cl₂.

(c) Write the half equations for oxidation, reduction and ionic equation for the redox reaction.


Answer:
(a) Bromine

(b) Iodine

(c)
$$\begin{array}{ll} \text { Oxidation half equation } & : 2 \mathrm{I}^{-} \rightarrow \mathrm{I}_2+2 \mathrm{e}^{-} \\ \text {Reduction half equation } & : \mathrm{Br}_2+2 \mathrm{e}^{-} \rightarrow 2 \mathrm{Br}^{-} \\ \text {Ionic equation } & : 2 \mathrm{I}^{-}+\mathrm{Br}_2 \rightarrow \mathrm{I}_2+2 \mathrm{Br}^{-} \end{array}$$

Question 5:
Based on the E⁰ value, arrange the following atom or ion in an ascending order of the strength of oxidising agent and reducing agent.
$$\begin{array}{ll} \mathrm{P} \rightleftharpoons \mathrm{P}^{2+}(\mathrm{aq})+2 \mathrm{e} & \mathrm{E}^0=-0.85 \mathrm{~V} \\ \mathrm{Q} \rightleftharpoons \mathrm{Q}^{3+}(\mathrm{aq})+3 \mathrm{e}^{-} & \mathrm{E}^0=+1.66 \mathrm{~V} \\ \mathrm{R} \rightleftharpoons \mathrm{R}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} & \mathrm{E}^0=+2.87 \mathrm{~V} \end{array}$$


Answer:
Oxidising agent : R²⁺, Q²⁺, P²⁺

Reducing agent : P, Q, R