Edexcel IAL Chemistry 16.3 standard electrode conditions

Check every condition before calculating: gas pressure, 1 mol dm-3 ion concentrations and dilution from mixed salts all affect whether a half-cell is standard.

Exam points

Select 100 kPa hydrogen pressure and 1 mol dm-3 ion conditions for standard cells.
Calculate solution concentrations or masses needed to prepare a standard half-cell.

[Maximum number: 1]

An electrochemical cell is made from the electrode systems shown by these half-equations.

\begin{aligned} \mathrm{Ag}^{+}(\mathrm{aq})+\mathrm{e}^{-} & \rightleftharpoons \mathrm{Ag}(\mathrm{~s}) & E^{\ominus}=+0.80 \mathrm{~V} \\ \mathrm{VO}_{2}^{+}(\mathrm{aq})+2 \mathrm{H}^{+}(\mathrm{aq})+\mathrm{e}^{-} & \rightleftharpoons \mathrm{VO}^{2+}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l}) & E^{\ominus}=+1.00 \mathrm{~V} \end{aligned}

The apparatus used to measure the value for $E_{\text {cell }}^{\ominus}$ under standard conditions is shown.

Figure for Question 16.3—The standard electrode potential, Eo, is measured in conditions of: i 298 K temperature ii 100 kPa pressure of gases iii question 1 — Edexcel A-Level Chemistry A2

The electrolyte in the right-hand half-cell is prepared using equal volumes of

$1 \mathrm{~mol} \mathrm{dm}^{-3}$ acidified $\mathrm{VO}_{2}^{+}(\mathrm{aq})$ and $1 \mathrm{~mol} \mathrm{dm}^{-3}$ acidified $\mathrm{VO}^{2+}(\mathrm{aq})$

$2 \mathrm{~mol} \mathrm{dm}^{-3}$ acidified $\mathrm{VO}_{2}^{+}(\mathrm{aq})$ and $2 \mathrm{~mol} \mathrm{dm}^{-3}$ acidified $\mathrm{VO}^{2+}(\mathrm{aq})$

$1 \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{VO}_{2}^{+}(\mathrm{aq})$ and $1 \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{HCl}(\mathrm{aq})$

$1 \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{VO}^{2+}(\mathrm{aq})$ and $1 \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{HCl}(\mathrm{aq})$

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16.3—The standard electrode potential, Eo, is measured in conditions of: i 298 K temperature ii 100 kPa pressure of gases iii question 1