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Edexcel IAL Chemistry 16.4 standard hydrogen electrode

A full SHE diagram needs platinised platinum, H2 at 100 kPa, 1 mol dm-3 acid, 298 K, a salt bridge and a linked reference half-cell.

Syllabus
First assessment 2019
Course
Chemistry YCH11
Level
A2

Exam points

  • Label Pt or platinum black, H2 at 100 kPa, 1 mol dm-3 H+ and 298 K in diagrams.
  • Connect the SHE to another half-cell with a salt bridge and high-resistance voltmeter.
  • Explain why platinum black increases the rate of the H2 and H+ equilibrium.

16.4—The features of the standard hydrogen electrode and understand why a reference electrode is necessary question 1

[Maximum number: 5]

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 [Xe]4f145 d106 s2[\mathrm{Xe}] 4 \mathrm{f}^{14} 5 \mathrm{~d}^{10} 6 \mathrm{~s}^{2}.

Question (a)

(a)

Mercury(I) chloride, Hg2Cl2\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 (a) — Edexcel A-Level Chemistry A2

The half-equation for the calomel electrode is

Hg2Cl2( s)+2e−⇌2Hg(l)+2Cl−(aq)\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⊖=+0.24 VE^{\ominus}=+0.24 \mathrm{~V}.

[ 5 ]

Question (i)

(i)

Suggest why KCl crystals are needed in the outer tube of the electrode.

[ 1 ]

Question (ii)

(ii)

Add labels to complete the diagram of a standard hydrogen electrode. Include details of any essential conditions.
(3)

Figure for Question (ii) — Edexcel A-Level Chemistry A2
[ 3 ]

Question (iii)

(iii)

Suggest one advantage of using a calomel electrode, in place of a standard hydrogen electrode, when measuring a cell potential.

[ 1 ]
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