Edexcel IAL Chemistry A2 Topic 17 Transition Metals and their Chemistry

Pearson Edexcel IAL Chemistry syllabusChemistry YCH11First assessment 2019

Topic 17 questions move from definitions and electron configurations into ligands, complex ions, colour changes, catalysis and transition-metal redox chemistry.

Exam points

Classify transition metals by stable ions with incompletely filled d orbitals.
Deduce Period 4 d-block atom and ion configurations, including Cr and Cu exceptions.
Use ligand, complex-ion and colour evidence to interpret transition-metal reactions.

[Maximum number: 3]

This question is about transition metal complexes.

(a)

The bonding within the complex $\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]^{2+}$ is

covalent, dative covalent and ionic

covalent and dative covalent only

covalent only

dative covalent only

[ 1 ]

(b)

Which complex is tetrahedral?

$\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\right]$

$\left[\mathrm{Cu}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}(\mathrm{OH})_{2}\right]$

$\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]^{2+}$

$\left[\mathrm{CoCl}_{4}\right]^{2-}$

[ 1 ]

(c)

Which complex contains a bidentate ligand?

$\left[\mathrm{Co}\left(\mathrm{NH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NHCH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\right)_{2}\right]^{3+}$

$\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\left(\mathrm{H}_{2} \mathrm{O}\right)_{2}\right]^{2+}$

$\left[\mathrm{Ni}\left(\mathrm{NH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\right)_{3}\right]^{2+}$

$[\mathrm{Mn}(\text { EDTA })]^{2-}$

[ 1 ]

[Maximum number: 1]

A ligand must be an

electron-pair donor

electron-pair donor and negatively charged

electron-pair acceptor

electron-pair acceptor and negatively charged

[Maximum number: 1]

Diamminecopper(I) ions are not coloured because

the d orbitals in copper(I) cannot be split

the energy difference between the split d orbitals is outside the visible region of the spectrum

d-d transitions are not possible because the d orbitals are fully occupied

copper(I) complexes are readily oxidised

Aqueous sodium hydroxide was added to aqueous iron(II) sulfate and the mixture allowed to stand.

What would be observed?

□ A
□ B
□ C
□ D

Use this space for any rough working. Anything you write in this space will gain no credit.

[Maximum number: 1]

When aqueous ammonia is added to an aqueous solution of zinc sulfate, a white precipitate forms which dissolves in excess ammonia to give a colourless solution.

What types of reaction are occurring?
□ A
□ B
□ C
□ D

(Total for Question 8 = 1 mark)

[Maximum number: 5]

This question is about silver and silver compounds.
Glass decorations are made reflective by coating their inner surface with silver. This is achieved by using the reaction between silver nitrate solution, ammonia and glucose, under alkaline conditions.

Initially the colourless complex ion diamminesilver(I), $\left[\mathrm{Ag}\left(\mathrm{NH}_{3}\right)_{2}\right]^{+}$ , forms.

(a)

Explain the shape of $\left[\mathrm{Ag}\left(\mathrm{NH}_{3}\right)_{2}\right]^{+}$ .

[ 3 ]

(b)

Explain why $\left[\mathrm{Ag}\left(\mathrm{NH}_{3}\right)_{2}\right]^{+}$ is colourless.

[ 2 ]

(a)

Explain, in terms of electronic structure, why iron(III) compounds are more stable than iron(II) compounds.

[ 2 ]

(b)

Invertebrates use a copper complex, haemocyanin, to transport oxygen. Blue oxyhaemocyanin gives invertebrate blood its characteristic colour.

Explain why oxyhaemocyanin and oxyhaemoglobin have different colours.
(3)

[ 3 ]

(c)

The presence of iron in sodium carbonate can affect its properties; the higher the quality of the sodium carbonate, the lower the proportion of iron.

The proportion of iron in a laboratory grade anhydrous sodium carbonate was listed as less than 20 ppm by mass.

In an experiment to check this specification, 20 g of the sodium carbonate was dissolved in sulfuric acid, and thioglycolic acid added in excess to form the iron(III) thioglycolic acid complex, $\mathrm{Fe}\left(\mathrm{HSCH}_{2} \mathrm{COOH}\right)_{3}^{3+}$ . The solution was made up to $500 \mathrm{~cm}^{3}$ in a volumetric flask and thoroughly mixed.

Colorimeter calibration graph

The transmittance of the resulting solution was determined using a colorimeter and found to be 39.8%.

[ 2 ]

(i)

Suggest what type of ligand thioglycolic acid is in the iron(III) thioglycolic acid complex. Justify your answer.
(2)

[ 2 ]

(d)

lodide ions are oxidised to iodine by peroxodisulfate ions.

2 \mathrm{I}^{-}(\mathrm{aq})+\mathrm{S}_{2} \mathrm{O}_{8}^{2-}(\mathrm{aq}) \rightarrow \mathrm{I}_{2}(\mathrm{aq})+2 \mathrm{SO}_{4}^{2-}(\mathrm{aq})

Iron(II) ions act as a homogeneous catalyst for this reaction.

[ 4 ]

(i)

State why the catalyst is described as 'homogeneous'.
(e) lodide ions are oxidised to iodine by peroxodisulfate ions.
(i) State why the catalyst is described as 'homogeneous'.
(i) State why the catalyst is described as 'homogeneous'.

[ 1 ]

(ii)

Write two equations to show how iron(II) ions catalyse this oxidation. State symbols are not required.

[ 2 ]

(iii)

Suggest how iron(II) ions lower the activation energy of this reaction.

[ 1 ]

(e)

Give a possible reason why the chloro complexes of iron ions have a coordination number of four rather than six.
(1)

[ 1 ]

Exam points

Question 1

Question 1(a)

Question 1(b)

Question 1(c)

Question 4

Question 5

Question 7

Question 8

Question 10

Question 10(a)(i)

Question 10(a)(ii)

Question 21

Question 21(a)

Question 21(c)

Question 21(d)

Question 21(d)(ii)

Question 21(e)

Question 21(e)(i)

Question 21(e)(ii)

Question 21(e)(iii)

Question 21(f)