Chemistry 9701 · AS & A Level · Group 17

Group 17 — practice question

Chlorine gas is produced by carrying out electrolysis of brine in a diaphragm cell.
(a(i))

Write half-equations, including state symbols, for the reactions taking place at each electrode in a diaphragm cell. Anode and cathode.

(a(ii))[3]

In the diaphragm cell, titanium is used for the anode and steel for the cathode. Suggest why steel is never chosen for the anode.

(b)[4]

Chlorine is highly reactive and forms compounds by direct combination with many elements. Describe what you would observe when chlorine is passed over separate heated samples of sodium and phosphorus. In each case, write an equation for the reaction.

(c)[4]

Chlorine reacts with aqueous sodium hydroxide in two different ways, depending on the conditions. In each situation, water, sodium chloride and one further chlorine-containing compound are produced. For each condition below, give the formula of the other chlorine-containing compound and state chlorine's oxidation number in it. Conditions: cold dilute NaOH(aq); hot concentrated NaOH(aq).

(d)[5]

Magnesium chloride, $\text{MgCl}_2$, and silicon tetrachloride, $\text{SiCl}_4$, each either dissolve in or react with water. Suggest the approximate pH of the solution formed in each case. Explain the difference between the two values, using an equation.

Worked solution & mark scheme

This 16-mark question has a full step-by-step worked solution and mark scheme. One marking point: Anode half-equation: $Cl^- (aq) \rightarrow \tfrac{1}{2}Cl_2(g) + e^-$

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