Chemistry 9701 · AS & A Level · Chemistry of transition elements

Chemistry of transition elements — practice question

Copper, with atomic number $29$, is a transition element.
(a)[2]

Fill in the electronic configurations for a Cu atom and a $\text{Cu}^+$ ion. Cu atom: $1\text{s}^22\text{s}^22\text{p}^6\,\ldots$ $\text{Cu}^+$ ion: $1\text{s}^22\text{s}^22\text{p}^6\,\ldots$

(b)[2]

$\text{Cu}^+$ ions form a linear complex with $\text{Cl}^-$ ions, and these are monodentate ligands. Draw the structure of this complex and show its overall charge.

(c)[2]

In aqueous solution, $\text{Cu}^{2+}$ ions are present as $[\text{Cu}(\text{H}_2\text{O})_6]^{2+}$ complex ions. Complete a three-dimensional diagram to show this complex's shape. Name the shape. Mark and state the value of one bond angle.

(d)[4]

If $\text{NH}_3(\text{aq})$ is added to $\text{Cu}^{2+}(\text{aq})$, first dropwise and then in excess, the two reactions below take place: $[\text{Cu}(\text{H}_2\text{O})_6]^{2+} \xrightarrow{\text{dropwise } \text{NH}_3(\text{aq})}$ A $\xrightarrow{\text{excess } \text{NH}_3(\text{aq})}$ B For each stage, describe the observations and write an equation.

(e(i))[1]

$\text{EDTA}^{4-}$ is a polydentate ligand. When a solution of $\text{EDTA}^{4-}$ is added to a solution containing $[\text{Cu}(\text{H}_2\text{O})_6]^{2+}$, a new complex forms. The formula of this complex is $[\text{CuEDTA}]^{2-}$. Name the kind of reaction occurring here.

(e(ii))[1]

Write the stability constant expression, $K_{\text{stab}}$, for $[\text{CuEDTA}]^{2-}$ in this reaction.

(e(iii))[1]

The value of the $K_{\text{stab}}$ of $[\text{CuEDTA}]^{2-}$ is $6.3 \times 10^{19}$ at $298\,\text{K}$. State what this indicates about the $[\text{CuEDTA}]^{2-}$ complex ion.

(f(i))[2]

Ethanedioate ions, $\text{C}_2\text{O}_4^{2-}$, can behave as a bidentate ligand. Explain what the term bidentate ligand means.

(f(ii))[2]

When ethanedioate ions are added to a solution of zirconium ions, $\text{Zr}^{4+}$, a complex ion containing four $\text{C}_2\text{O}_4^{2-}$ ions and one $\text{Zr}^{4+}$ ion is produced. All four ethanedioate ions act as bidentate ligands in this complex. Give the formula of this complex ion and explain why it is not octahedral.

Worked solution & mark scheme

This 17-mark question has a full step-by-step worked solution and mark scheme. One marking point: Electron configuration of Cu correctly given: $3s^23p^63d^{10}4s^1$ or $3s^23p^63d^{10}$

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