Edexcel IAL Chemistry 16.5 measuring electrode potentials

Decide whether the half-cell needs a metal electrode or inert platinum, then choose soluble salts, 1 mol dm-3 solutions and a nitrate salt bridge.

Exam points

Choose metal electrodes for metal half-cells and platinum for ion-only systems.
Identify KNO3 salt bridges and 1 mol dm-3 Fe2+/Fe3+ or other soluble ion solutions.
Explain that salt bridges allow ion flow while wires carry electrons only.

[Maximum number: 2]

This question is about cell reactions involving chromium.
Use your Data Booklet when answering this question.

A student set up the following apparatus to measure the standard electrode potential for right-hand electrode system 8 in your Data Booklet.

Figure for Question 16.5—Different methods are used to measure standard electrode potentials of: i metals or non-metals in contact with their ions question 1 — Edexcel A-Level Chemistry A2

Identify X and Y.

X:

Y:

platinum / Pt

- $1 \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{Cr}^{2+}$ and

$1 \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{Cr}^{3+}$

Accept platinised platinum / platinum black

Allow $1 \mathrm{~mol} \mathrm{dm}^{-3}$ named soluble chromium(II) salts

Allow named soluble chromium(III) salts giving $1 \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{Cr}^{3+}$ solution

Allow $1 \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{Cr}^{2+}$ and $\mathrm{Cr}^{3+}$

Ignore equimolar

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16.5—Different methods are used to measure standard electrode potentials of: i metals or non-metals in contact with their ions question 1