Edexcel A-Level Chemistry A2 16.7 A Standard Emf Eocell By Combining Two Standard Electrode Potentials Questions

Practise Edexcel IAL Chemistry 16.7 by calculating standard cell emf, deducing unknown electrode potentials and selecting feasible reaction directions from positive E°cell values.

Exam points

Calculate E°cell from Data Booklet values using right minus left or equivalent.
Deduce unknown electrode potentials from measured emf and a reference half-cell.
Use positive E°cell to choose reaction direction and combine balanced half-equations.

[Maximum number: 1]

This question is about mercury, Hg, and its compounds.
Mercury is a liquid element in the same group of the Periodic Table as zinc.
The electronic configuration of mercury is $[\mathrm{Xe}] 4 \mathrm{f}^{14} 5 \mathrm{~d}^{10} 6 \mathrm{~s}^{2}$ .

Mercury(I) chloride, $\mathrm{Hg}_{2} \mathrm{Cl}_{2}$ , is also known as calomel.

A saturated calomel electrode may be used as an alternative to the standard hydrogen electrode.

Figure for Question Edexcel A-Level Chemistry A2 16.7 A Standard Emf Eocell By Combining Two Standard Electrode Potentials Questions question 1 — Edexcel A-Level Chemistry A2

The half-equation for the calomel electrode is

\mathrm{Hg}_{2} \mathrm{Cl}_{2}(\mathrm{~s})+2 \mathrm{e}^{-} \rightleftharpoons 2 \mathrm{Hg}(\mathrm{l})+2 \mathrm{Cl}^{-}(\mathrm{aq})

The standard electrode potential of the calomel electrode is $E^{\ominus}=+0.24 \mathrm{~V}$ .

A calomel electrode was used to measure the standard electrode potential of the $\mathrm{Sn}^{2+}(\mathrm{aq}) \mid \mathrm{Sn}(\mathrm{s})$ half-cell.

The reading on the voltmeter in this cell was +0.37 V .
Deduce the standard electrode potential for the $S n^{2+}(a q) \mid S n(s)$ half-cell.

An answer that makes reference to the following point:

- $(0.24-0.37=)-0.13(\mathrm{~V})$

Ignore working, even if incorrect

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Edexcel A-Level Chemistry A2 16.7 A Standard Emf Eocell By Combining Two Standard Electrode Potentials Questions question 1