CAIE A-Level Chemistry 24.2.7 Constructing Cell Redox Equations

Practise selecting, reversing and scaling half-equations so electrons cancel in the overall cell reaction.

Exam points

write both reduction half-equations first, then reverse the one that undergoes oxidation
multiply equations to equalise electron numbers while leaving electrode potentials unchanged
add and cancel electrons and common species, then verify atoms and total charge in the result

[Maximum number: 1]

Titanium is a transition element in Period 4. It is commonly found as $\mathrm{TiO}_{2}$ in minerals.

The $\mathrm{TiO}^{2+}$ ion forms when $\mathrm{TiO}_{2}$ reacts with an excess of sulfuric acid.
$\mathrm{TiO}^{2+}$ can be reduced by zinc metal in acidic conditions to form a purple solution containing $\mathrm{Ti}^{3+}(\mathrm{aq})$ .

Write an ionic equation for the reduction of $\mathrm{TiO}^{2+}$ by zinc metal in acidic conditions.

$2 \mathrm{TiO}^{2+}+4 \mathrm{H}^{+}+\mathrm{Zn} \rightarrow 2 \mathrm{Ti}^{3+}+2 \mathrm{H}_{2} \mathrm{O}+\mathrm{Zn}^{2+}$

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24.2.7—Redox equations using the relevant question 1