A LevelChemistryEdexcelExam Questions6. Advanced Inorganic Chemistry (A Level Only)6.3 Reactions of Transition Metal Elements

Reactions of Transition Metal Elements (Edexcel A Level Chemistry)

Exam Questions

47 mins3 questions
Medium
Hard
1a1 mark

This question is about the properties of transition elements, their ions and their complexes.

Give the oxidation state of vanadium in the compound NH4VO3.

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1b7 marks

Excess zinc powder is added to an acidified solution of the compound NH4VO3.
Using the data in the table, explain the sequence of reactions that takes place. 

In your answer, include a description of what you would see, and the relevant ionic equations with their calculated E subscript cell superscript ⦵ values. State symbols are not required.

Electrode system bold italic E to the power of bold ⦵ bold space bold divided by bold V
straight V to the power of 2 plus end exponent left parenthesis aq right parenthesis space plus space 2 straight e to the power of minus space rightwards harpoon over leftwards harpoon space straight V left parenthesis straight s right parenthesis −1.18
straight V to the power of 3 plus end exponent left parenthesis aq right parenthesis space plus space straight e to the power of minus space rightwards harpoon over leftwards harpoon space straight V to the power of 2 plus end exponent left parenthesis aq right parenthesis −0.26
VO to the power of 2 plus end exponent left parenthesis aq right parenthesis space plus space 2 straight H to the power of plus open parentheses aq close parentheses plus space straight e to the power of minus space rightwards harpoon over leftwards harpoon space straight V to the power of 3 plus end exponent open parentheses aq close parentheses space plus space straight H subscript 2 straight O open parentheses straight l close parentheses +0.34
VO subscript 3 superscript minus space left parenthesis aq right parenthesis space plus space 4 straight H to the power of plus left parenthesis aq right parenthesis space plus space straight e to the power of negative space end exponent rightwards harpoon over leftwards harpoon space VO to the power of 2 plus end exponent left parenthesis aq right parenthesis space plus space 2 straight H subscript 2 straight O left parenthesis straight l right parenthesis +1.00
Zn to the power of 2 plus end exponent left parenthesis aq right parenthesis space plus space 2 straight e to the power of minus space rightwards harpoon over leftwards harpoon space Zn left parenthesis straight s right parenthesis −0.76

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1c2 marks

Explain how vanadium(V) oxide acts as a catalyst in one step of the contact process. The equation for this step is

2SO2 (g) + O2 (g) rightwards harpoon over leftwards harpoon2SO3 (g)

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1d6 marks

Describe the reactions of separate portions of aqueous copper(II) ions with aqueous sodium hydroxide solution, with excess aqueous ammonia solution and with concentrated hydrochloric acid.

In your answer you should link observations with equations which include the formulae of any copper-containing complex ions. Include state symbols.

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1a4 marks

This question is about transition metals and transition metal complexes.

Describe the bonding in the element chromium and use your answer to justify why it has such a high melting temperature.

You may find it helpful to draw a labelled diagram.

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1b4 marks

When chromium(III) sulfate dissolves in water, a green solution containing the [Cr(H2O)6]3+ ion forms.

i)
Give the shape of this complex ion.

(1)

ii)
Explain why the chromium complex ion is coloured.

(3)

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1c3 marks

The ligand ethylenediaminetetraacetate, EDTA4−, has the structure shown.


q3c-9cho-al-1-nov-2020-qp-edexcel-a-level-chem

When a solution of EDTA4− is added to a solution of [Cr(H2O)6]3+ ions, a new complex ion is formed.


[Cr(H2O)6]3+ + EDTA4− ⇌ [Cr(EDTA)]− + 6H2O


The equilibrium constant for this equilibrium is 2.51 × 1023 dm3 mol−1.

By considering the equilibrium for this reaction and changes in entropy, comment on the value of the equilibrium constant. No calculations are required.

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1d
Sme Calculator5 marks

Aqueous vanadium(II) chloride, VCl2 (aq), can be oxidised by bubbling gaseous chlorine, Cl2 (g), through the solution in the absence of air.

40.0 cm3 of 0.100 mol dm−3 VCl2 solution was oxidised by 144 cm3 of chlorine gas, at room temperature and pressure (r.t.p.).
The chlorine was reduced to chloride ions, according to the half-equation

Cl2 (g) + 2e− → 2Cl− (aq)

[Molar volume of a gas at r.t.p. = 24.0 dm3 mol−1]

i)
Use these data to calculate the final oxidation state of vanadium. 
You must show your working.

(5)

ii)
State the initial and final colours you would see as the chlorine bubbles through the aqueous vanadium(II) chloride, VCl2 (aq).

(2)

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2a2 marks

This is a question about chromium(III) and chromium(VI) compounds.

Describe the observations when aqueous sodium hydroxide is added drop by drop until in excess to a solution of chromium(III) ions.

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2b6 marks

The chromium(III) complex, [Cr(OH)6]3−, can be oxidised to chromate(VI) ions, CrO42−, by hydrogen peroxide solution.

i)
Deduce the oxidation half-equation for this reaction, which takes place in alkaline conditions. State symbols are not required.

(2)

ii)
If the solution of chromate(VI) ions is then acidified, the colour of the solution changes to orange as dichromate(VI) ions form.

Write the equation for this change. State symbols are not required.
(1)

iii)
In acidic conditions, dichromate(VI) ions can also be reduced to chromium(III) ions using hydrogen peroxide.

The value of  E to the power of ⊖ subscript cell = + 0.65V for which the cell diagram is


Pt (s)│H2O2 (aq), [2H+ (aq) + O2 (g)] parallel to [Cr2O72− (aq) + 14H+ (aq)], [2Cr3+ (aq) + 7H2O (l)]│Pt (s)

Deduce from the cell diagram the oxidation and the reduction half-equations, and thus the overall equation for this reaction.
State symbols are not required.

(3)

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2c7 marks

Draw a labelled diagram of the apparatus that you would use to measure the standard emf of a cell with a zinc-zinc(II) electrode system and a chromium(III)-dichromate(VI) electrode system.

Include the formulae of all the compounds required and the concentrations of the solutions.

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