CAIE A-Level Chemistry A2 24.2.3 Measuring Standard Electrode Potentials Topic Practice

Hypophosphorous acid is an inorganic acid.
The conjugate base of hypophosphorous acid is $\mathrm{H}_{2} \mathrm{PO}_{2}^{-}$.

$\mathrm{H}_{2} \mathrm{PO}_{2}^{-}$is a strong reducing agent. It can be used to reduce metal cations without the need for electrolysis.
equation $1 \quad \mathrm{HPO}_{3}^{2-}+2 \mathrm{H}_{2} \mathrm{O}+2 \mathrm{e}^{-} \rightleftharpoons \mathrm{H}_{2} \mathrm{PO}_{2}^{-}+3 \mathrm{OH}^{-}$$E^{\ominus}=-1.57 \mathrm{~V}$

Complete the diagram in Fig. 2.1 to show how the standard electrode potential of the $\mathrm{Cr}^{3+} / \mathrm{Cr}$ half-cell can be measured relative to that of the standard hydrogen electrode.

Identify the chemicals, conditions and relevant pieces of apparatus.