Chemistry 9701 · AS & A Level · Electrochemistry

Electrochemistry — practice question

(a) Nickel(II) iodate(V), Ni(IO$_3$)$_2$, has only slight solubility in water. At 298 K, the concentration of a saturated solution is $2.30 \times 10^{-2}\,\text{mol dm}^{-3}$.
(a(i))[2]

Complete the solubility product expression, $K_{sp}$, for Ni(IO$_3$)$_2$, and include the units.

(a(ii))[1]

Calculate the numerical value of $K_{sp}$ for Ni(IO$_3$)$_2$ at 298 K.

(b(i))[1]

Use this information to work out $E^\circ_{cell}$. State which electrode is positive.

(b(ii))[1]

Suggest how the measured $E_{cell}$ compares with $E^\circ_{cell}$ under standard conditions. Explain your answer.

(b(iii))[2]

Complete Table 3.1 by using one tick ($\checkmark$) to show how the $E_{cell}$ of this cell changes when a small amount of NiSO$_4$(aq) is added to the beaker containing Ni(IO$_3$)$_2$(aq) and I$_2$(aq) in Fig. 3.1. Explain your answer.

(c(i))[1]

Calculate $[\text{H}^+(aq)]$, in $\text{mol dm}^{-3}$, for a $1.0\,\text{mol dm}^{-3}$ solution of HIO$_3$.

(c(ii))[1]

Use your answer from (c)(i) to calculate the equilibrium concentrations of HIO$_3$(aq) and IO$_3^-(aq), in $\text{mol dm}^{-3}$, for a $1.0\,\text{mol dm}^{-3}$ solution of HIO$_3$.

(c(iii))[1]

Use your answers from (c)(i) and (c)(ii) to calculate the $K_a$, in $\text{mol dm}^{-3}$, of HIO$_3$.

(d(i))[2]

Define buffer solution.

(d(ii))[2]

Use the information to calculate the rate constant, $k$, and state its units.

(d(iii))[1]

The reaction is carried out again at the same temperature and with the same starting values of $[\text{IO}_3^-]$ and $[\text{I}^-]$. $[\text{H}^+]$ is raised to $3.00 \times 10^{-2}\,\text{mol dm}^{-3}$. Calculate the initial rate of the reaction.

Worked solution & mark scheme

This 15-mark question has a full step-by-step worked solution and mark scheme. One marking point: $K_{sp} = [\mathrm{Ni^{2+}}][\mathrm{IO_3^-}]^2$

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