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Date May 2021 Marks available 2 Reference code 21M.2.hl.TZ1.3
Level HL Paper 2 Time zone TZ1
Command term Deduce Question number 3 Adapted from N/A

Question

Magnetite, Fe3O4, is another ore of iron that contains both Fe2+ and Fe3+.

Iron exists as several isotopes.

Deduce the ratio of Fe2+:Fe3+ in Fe3O4.

[1]
a.

State the type of spectroscopy that could be used to determine their relative abundances.

[1]
b(i).

State the number of protons, neutrons and electrons in each species.

[2]
b(ii).

Iron has a relatively small specific heat capacity; the temperature of a 50 g sample rises by 44.4°C when it absorbs 1 kJ of heat energy.

Determine the specific heat capacity of iron, in J g−1 K−1. Use section 1 of the data booklet.

[1]
c.

A voltaic cell is set up between the Fe2+ (aq) | Fe (s) and Fe3+ (aq) | Fe2+ (aq) half-cells.

Deduce the equation and the cell potential of the spontaneous reaction. Use section 24 of the data booklet.

[2]
d.

The figure shows an apparatus that could be used to electroplate iron with zinc. Label the figure with the required substances.

[2]
e.

Outline why, unlike typical transition metals, zinc compounds are not coloured.

[1]
f.

Transition metals like iron can form complex ions. Discuss the bonding between transition metals and their ligands in terms of acid-base theory.

[2]
g.

Markscheme

1:2 ✔

Accept 2 Fe3+: 1 Fe2+
Do not accept 2:1 only

a.

mass «spectroscopy»/MS ✔

b(i).


Award [1 max] for 4 correct values.

b(ii).

specific heat capacity « = qm×T/1000J50g×44K» = 0.45 «J g−1 K−1» ✔

c.

Equation:
2Fe3+(aq) + Fe(s) → 3Fe2+(aq) ✔

Cell potential:
«+0.77 V − (−0.45 V) = +»1.22 «V» ✔


Do not accept reverse reaction or equilibrium arrow.

Do not accept negative value for M2.

d.

left electrode/anode labelled zinc/Zn AND right electrode/cathode labelled iron/Fe ✔

electrolyte labelled as «aqueous» zinc salt/Zn2+


Accept an inert conductor for the anode.

Accept specific zinc salts such as ZnSO4.

e.

« Zn2+» has a full d-shell
OR
does not form « ions with» an incomplete d-shell ✔


Do not accept “Zn is not a transition metal”.

Do not accept zinc atoms for zinc ions.

f.

ligands donate pairs of electrons to metal ions
OR
forms coordinate covalent/dative bond✔

ligands are Lewis bases
AND
metal «ions» are Lewis acids ✔

g.

Examiners report

[N/A]
a.
[N/A]
b(i).
[N/A]
b(ii).
[N/A]
c.
[N/A]
d.
[N/A]
e.
[N/A]
f.
[N/A]
g.

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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