Edexcel A-Level Chemistry A2 17.19 Redox Reactions for the Interconversion of the Oxidation States of Vanadium 5 4 3 And 2 In Terms of the Relevant Eo Questions

An answer that makes reference to the following points:

- equation for oxidation of $\mathrm{V}^{2+}$ to $\mathrm{V}^{3+}$

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- $E^{\circ}$ cell for oxidation of $\mathrm{V}^{2+}$ to $\mathrm{V}^{3+}$

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- equation for oxidation of $\mathrm{V}^{3+}$ to $\mathrm{VO}^{2+}$

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- $E^{\circ}{ }_{\text {cell }}$ for oxidation of $\mathrm{V}^{3+}$ to $\mathrm{VO}^{2+}$

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- $\mathrm{VO}^{2+}$ is not oxidised to $\mathrm{VO}_{2}{ }^{+} /$any further as $E^{\circ}$ cell is $-0.2(\mathrm{~V}) /$ negative

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Examples of equations:

Allow multiples Ignore state symbols even if incorrect Ignore uncancelled $\mathrm{H}^{+} / \mathrm{H}_{2} \mathrm{O}$

Penalise uncancelled electrons once only

$\mathrm{NO}_{3}{ }^{-}+2 \mathrm{H}^{+}+\mathrm{V}^{2+} \rightarrow \mathrm{NO}_{2}+\mathrm{H}_{2} \mathrm{O}+\mathrm{V}^{3+}$

Allow $\mathrm{Cu}^{2+}+\mathrm{V}^{2+} \rightarrow \mathrm{Cu}^{+}+\mathrm{V}^{3+}$

Allow $1 / 2 \mathrm{Br}_{2}+\mathrm{V}^{2+} \rightarrow \mathrm{Br}^{-}+\mathrm{V}^{3+}$$E^{\circ}{ }_{\text {cell }}=(+) 1.06(\mathrm{~V})$

TE on $\mathrm{Cu}^{2+} / \mathrm{Br}_{2}$ chosen as oxidising agent

With $\mathrm{Cu}^{2+} E^{\ominus}{ }_{\text {cell }}=(+) 0.41(0)(\mathrm{V})$

With $\mathrm{Br}_{2} E^{\circ}{ }_{\text {cell }}=(+) 1.35(\mathrm{~V})$$\mathrm{NO}_{3}{ }^{-}+\mathrm{V}^{3+} \rightarrow \mathrm{NO}_{2}+\mathrm{VO}^{2+}$

Allow $1 / 2 \mathrm{Br}_{2}+\mathrm{V}^{3+}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{Br}^{-}+\mathrm{VO}^{2+}+2 \mathrm{H}^{+}$$E^{\circ}{ }_{\text {cell }}=(+) 0.46(\mathrm{~V})$

With $\mathrm{Br}_{2} E^{\circ}{ }_{\text {cell }}=(+) 0.75(\mathrm{~V})$

Allow this shown in an equation

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