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Transition elements

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Question 2

This question is about some reactions of d-block elements and their ions.

Table 1 shows standard electrode potentials which will be needed within this question.

Half-reactionEθ/VZn2+(aq)+2e−⇌Zn(s)−0.76Ti3+(aq)+e−⇌Ti2+(aq)−0.37Ni2+(aq)+2e−⇌Ni(s)−0.25TiO2+(aq)+2H+(aq)+e−⇌Ti3+(aq)+H2O(l)+0.10I2(aq)+2e−⇌2I−(aq)+0.54Fe3+(aq)+e−⇌Fe2+(aq)+0.77H2O2(aq)+2H+(aq)+2e−⇌2H2O(l)+1.77\begin{array}{|l|c|} \hline \text{Half-reaction} & E^\theta / \text{V} \\ \hline \text{Zn}^{2+}(\text{aq}) + 2\text{e}^- \rightleftharpoons \text{Zn}(\text{s}) & -0.76 \\ \text{Ti}^{3+}(\text{aq}) + \text{e}^- \rightleftharpoons \text{Ti}^{2+}(\text{aq}) & -0.37 \\ \text{Ni}^{2+}(\text{aq}) + 2\text{e}^- \rightleftharpoons \text{Ni}(\text{s}) & -0.25 \\ \text{TiO}^{2+}(\text{aq}) + 2\text{H}^+(\text{aq}) + \text{e}^- \rightleftharpoons \text{Ti}^{3+}(\text{aq}) + \text{H}_2\text{O}(\text{l}) & +0.10 \\ \text{I}_2(\text{aq}) + 2\text{e}^- \rightleftharpoons 2\text{I}^-(\text{aq}) & +0.54 \\ \text{Fe}^{3+}(\text{aq}) + \text{e}^- \rightleftharpoons \text{Fe}^{2+}(\text{aq}) & +0.77 \\ \text{H}_2\text{O}_2(\text{aq}) + 2\text{H}^+(\text{aq}) + 2\text{e}^- \rightleftharpoons 2\text{H}_2\text{O}(\text{l}) & +1.77 \\ \hline \end{array}Half-reactionZn2+(aq)+2e−⇌Zn(s)Ti3+(aq)+e−⇌Ti2+(aq)Ni2+(aq)+2e−⇌Ni(s)TiO2+(aq)+2H+(aq)+e−⇌Ti3+(aq)+H2​O(l)I2​(aq)+2e−⇌2I−(aq)Fe3+(aq)+e−⇌Fe2+(aq)H2​O2​(aq)+2H+(aq)+2e−⇌2H2​O(l)​Eθ/V−0.76−0.37−0.25+0.10+0.54+0.77+1.77​​
a.

Complete the electron configuration of:

  • a Ni\text{Ni}Ni atom: 1s2 …1\text{s}^2 \ \dots1s2 …
  • a Ni2+\text{Ni}^{2+}Ni2+ ion: 1s2 …1\text{s}^2 \ \dots1s2 …
[2]
b.

A standard cell is set up in the laboratory with the cell reaction shown below:

Ni(s)+I2(aq)→Ni2+(aq)+2I−(aq) \text{Ni}(\text{s}) + \text{I}_2(\text{aq}) \rightarrow \text{Ni}^{2+}(\text{aq}) + 2\text{I}^-(\text{aq}) Ni(s)+I2​(aq)→Ni2+(aq)+2I−(aq)

Describe how this cell could be set up to measure its standard cell potential. Include details of the electrodes, solutions, salt bridge, and standard conditions required.

[3]
c.

Predict the standard cell potential of this cell.

[1]
d.

Use the information in Table 1 to help answer both parts of this question.

Write the overall equation for the oxidation of Fe2+\text{Fe}^{2+}Fe2+ by H2O2\text{H}_2\text{O}_2H2​O2​ in acidic conditions.

[1]
e.

Zinc reacts with acidified TiO2+\text{TiO}^{2+}TiO2+ ions to form Ti2+\text{Ti}^{2+}Ti2+ ions in two stages. Explain why this happens in terms of electrode potentials and equilibria. Include overall equations for the reactions which occur.

[3]
f.

Three different reactions of transition metal compounds are described below.

  • Reaction 1: Aqueous copper(II) sulfate reacts with excess concentrated hydrochloric acid in a ligand substitution reaction. A yellow-green solution is formed containing a tetrahedral complex ion, C.
  • Reaction 2: Copper(I) sulfate dissolves in water to undergo a disproportionation reaction, forming a blue solution, D, and a red-brown solid precipitate, E.
  • Reaction 3: Nickel(II) carbonate reacts with warm dilute nitric acid in a neutralisation reaction to form a green solution. Unreacted nickel(II) carbonate is filtered off, and the remaining solution is evaporated to allow a hydrated salt, F, to crystallise. The hydrated salt, F, has the percentage composition by mass: Ni\text{Ni}Ni, 20.18%; N\text{N}N, 9.64%; H\text{H}H, 4.16%; O\text{O}O, 66.02%.

Identify C–F by formulae or structures, as appropriate. Include equations, any changes in oxidation number, and working.

[6]

Transition elements Questions

  1. A Level
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  3. /Transition elements