When lead iodide, ${\mathrm{PbI}}_2$ is electrolysed, the following reactions occur:
${\mathrm{Pb}}^{2+} + 2{\mathrm{e}}^{-} \to \mathrm{Pb}$ and
$2{\mathrm{I}}^{-} \to {\mathrm{I}}_2 +2{\mathrm{e}}^{-}$

Which of these equations describes the reaction at the cathode? Explain your answer.

State the oxidation number change of each iodide ion in the reaction: $2{\mathrm{I}}^{-} \to {\mathrm{I}}_2 + 2{\mathrm{e}}^{-}$

Calculate the volume of hydrogen produced at r.t.p. when a concentrated aqueous solution of sulfuric acid is electrolysed for $15.0 \min$ using a current of $1.40 \mathrm{A}$. ($\mathrm{F}= 96500 \mathrm{C} {\mathrm{mol}}^{-1}$; $1 \mathrm{mole}$ of gas occupies $24.0 {\mathrm{dm}}^3$ at r.t.p.) (Write the value only rounded off to two decimal places)

A learner passed a constant electric current of $0.15 \mathrm{A}$ through a solution of silver nitrate, using pure silver electrodes, for $45 \min$ exactly. The mass of the anode decreased by $0.45 \mathrm{g}$. Use this data to calculate the charge on a mole of electrons. (A_r value: $\left[\mathrm{Ag}\right] = 108$)

Refer to the list of electrode potentials below to answer the question.

${\mathrm{Ag}}^{+} \left(\mathrm{aq}\right) +{\mathrm{e}}^{-} \rightleftharpoons \mathrm{Ag}\left(\mathrm{s}\right)$          voltage $= +0.80 \mathrm{V}$

${\mathrm{Co}}^{2+}\left(\mathrm{aq}\right) + 2{\mathrm{e}}^{-} \rightleftharpoons \mathrm{Co}\left(\mathrm{s}\right)$        voltage $= -0.28 \mathrm{V}$

${\mathrm{Cu}}^{2+}\left(\mathrm{aq}\right) + 2{\mathrm{e}}^{-} \rightleftharpoons \mathrm{Cu}\left(\mathrm{s}\right)$    voltage $= +0.34 \mathrm{V}$

${\mathrm{Pb}}^{2+} \left(\mathrm{aq}\right) + 2{\mathrm{e}}^{-} \rightleftharpoons \mathrm{Pb}\left(\mathrm{s}\right)$   voltage $= -0.13 \mathrm{V}$

${\mathrm{Zn}}^{2+}\left(\mathrm{aq}\right) + 2{\mathrm{e}}^{-} \rightleftharpoons \mathrm{Zn}\left(\mathrm{s}\right)$     voltage $= -0.76 \mathrm{V}$

Which metal in the list is the best reducing agent?

Refer to the list of electrode potentials below to answer the question.

${\mathrm{Ag}}^{+} \left(\mathrm{aq}\right) +{\mathrm{e}}^{-} \rightleftharpoons \mathrm{Ag}\left(\mathrm{s}\right)$          voltage $= +0.80 \mathrm{V}$

${\mathrm{Co}}^{2+}\left(\mathrm{aq}\right) + 2{\mathrm{e}}^{-} \rightleftharpoons \mathrm{Co}\left(\mathrm{s}\right)$      voltage $= -0.28 \mathrm{V}$

${\mathrm{Cu}}^{2+}\left(\mathrm{aq}\right) + 2{\mathrm{e}}^{-} \rightleftharpoons \mathrm{Cu}\left(\mathrm{s}\right)$    voltage $= +0.34 \mathrm{V}$

${\mathrm{Pb}}^{2+} \left(\mathrm{aq}\right) + 2{\mathrm{e}}^{-} \rightleftharpoons \mathrm{Pb}\left(\mathrm{s}\right)$   voltage $= -0.13 \mathrm{V}$

${\mathrm{Zn}}^{2+}\left(\mathrm{aq}\right) + 2{\mathrm{e}}^{-} \rightleftharpoons \mathrm{Zn}\left(\mathrm{s}\right)$     voltage $= -0.76 \mathrm{V}$

Which metal ion in the list is most difficult to reduce?