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Date May 2017 Marks available 1 Reference code 17M.2.hl.TZ2.2
Level HL Paper 2 Time zone TZ2
Command term Calculate Question number 2 Adapted from N/A

Question

An acidic sample of a waste solution containing Sn2+(aq) reacted completely with K2Cr2O7 solution to form Sn4+(aq).

Identify one organic functional group that can react with acidified K2Cr2O7(aq).

[1]
a.v.

Corrosion of iron is similar to the processes that occur in a voltaic cell. The initial steps involve the following half-equations:

Fe2+(aq) + 2e Fe(s)

1 2 O2(g) + H2O(l) + 2e 2OH(aq)

Calculate Eθ, in V, for the spontaneous reaction using section 24 of the data booklet.

[1]
b.i.

Calculate the Gibbs free energy, ΔGθ, in kJ, which is released by the corrosion of 1 mole of iron. Use section 1 of the data booklet.

[2]
b.ii.

Explain why iron forms many different coloured complex ions.

[3]
b.iii.

Zinc is used to galvanize iron pipes, forming a protective coating. Outline how this process prevents corrosion of the iron pipes.

[1]
c.

Markscheme

hydroxyl/OH
OR
aldehyde/CHO

 

Accept “hydroxy/alcohol” for “hydroxyl”.

Accept amino/amine/NH2.

[1 mark]

a.v.

«Eθ =» +0.85 «V»

 

Accept 0.85 V.

[1 mark]

b.i.

ΔGθ «= –nFEθ» = –2 «mol e» x 96500 «C mol–1» x 0.85 «V»

«ΔGθ =» –164 «kJ»

 

Accept “«+»164 «kJ»” as question states energy released.

Award [1 max] for “+” or “–” 82 «kJ».

Do not accept answer in J.

[2 marks]

b.ii.

incompletely filled d-orbitals

colour depends upon the energy difference between the split d-orbitals

variable/multiple/different oxidation states

different «nature/identity of» ligands

different number of ligands

[3 marks]

b.iii.

Zn/zinc is a stronger reducing agent than Fe/iron
OR
Zn/zinc is oxidized instead of Fe/iron
OR
Zn/zinc is the sacrificial anode

 

Accept “Zn is more reactive than Fe”.

Accept “Zn oxide layer limits further corrosion”.

Do not accept “Zn layer limits further corrosion”.

[1 mark]

c.

Examiners report

[N/A]
a.v.
[N/A]
b.i.
[N/A]
b.ii.
[N/A]
b.iii.
[N/A]
c.

Syllabus sections

Additional higher level (AHL) » Topic 19: Redox processes » 19.1 Electrochemical cells
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Additional higher level (AHL) » Topic 19: Redox processes
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