| Date | May 2021 | Marks available | 1 | Reference code | 21M.2.hl.TZ1.3 |
| Level | HL | Paper | 2 | Time zone | TZ1 |
| Command term | Outline | 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.
State the type of spectroscopy that could be used to determine their relative abundances.
State the number of protons, neutrons and electrons in each species.
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.
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.
The figure shows an apparatus that could be used to electroplate iron with zinc. Label the figure with the required substances.
Outline why, unlike typical transition metals, zinc compounds are not coloured.
Transition metals like iron can form complex ions. Discuss the bonding between transition metals and their ligands in terms of acid-base theory.
Markscheme
1:2 ✔
Accept 2 Fe3+: 1 Fe2+
Do not accept 2:1 only
mass «spectroscopy»/MS ✔
Award [1 max] for 4 correct values.
specific heat capacity « = » = 0.45 «J g−1 K−1» ✔
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.
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.
« 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.
ligands donate pairs of electrons to metal ions
OR
forms coordinate covalent/dative bond✔
ligands are Lewis bases
AND
metal «ions» are Lewis acids ✔
Examiners report
Syllabus sections
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22M.1.hl.TZ1.8:
Why is hydrated copper (II) sulfate blue?
A. Blue light is emitted when electrons return to lower d-orbitals.
B. Light complimentary to blue is absorbed when electrons return to lower d-orbitals.
C. Blue light is emitted when electrons are promoted between d-orbitals.
D. Light complimentary to blue is absorbed when electrons are promoted between d-orbitals.
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17N.1.hl.TZ0.10:
[CoCl6]3– is orange while [Co(NH3)6]3+ is yellow. Which statement is correct?
A. [CoCl6]3– absorbs orange light.
B. The oxidation state of cobalt is different in each complex.
C. The different colours are due to the different charges on the complex.
D. The different ligands cause different splitting in the 3d orbitals.
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22M.1.hl.TZ2.8:
[Cr(OH2)6]3+ is violet and [Cr(NH3)6]3+ is yellow. What is correct?
The Colour Wheel
- 18M.1.hl.TZ1.8: Which complex has the greatest d orbital splitting?
- 18M.1.hl.TZ2.8: Part of the spectrochemical series is shown for transition metal complexes. I−< Cl− <...
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19M.3.hl.TZ1.3b(i):
Identify the colour of the emission spectrum of lithium using section 17 of the data booklet.
- 19M.1.hl.TZ2.6: How is colour produced in transition metal complexes? A. Light is absorbed when electrons...
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17M.2.hl.TZ2.2b.iii:
Explain why iron forms many different coloured complex ions.
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18N.3.hl.TZ0.1c:
Copper(II) ion solutions are blue. Suggest, giving your reason, a suitable wavelength of light for the analysis.
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19N.2.hl.TZ0.6f(iv):
Examine the relationship between the Brønsted–Lowry and Lewis definitions of a base, referring to the ligands in the complex ion [CuCl4]2−.
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19N.2.hl.TZ0.6f(ii):
Deduce why the Cu(I) solution is colourless.
-
19N.2.hl.TZ0.6f(i):
Describe how the blue colour is produced in the Cu(II) solution. Refer to section 17 of the data booklet.
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16N.1.hl.TZ0.9:
The oxidation state of cobalt in the complex ion [Co(NH3)5Br]x is +3. Which of the following statements are correct?
I. The overall charge, x, of the complex ion is 2+.
II. The complex ion is octahedral.
III. The cobalt(III) ion has a half-filled d-subshell.A. I and II only
B. I and III only
C. II and III only
D. I, II and III
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16N.1.hl.TZ0.10:
What is the correct explanation for the colour of [Cu(H2O)6]2+?
A. Light is absorbed when an electron moves to a d orbital of higher energy.
B. Light is released when an electron moves to a d orbital of higher energy.
C. Light is absorbed when electrons move from the ligands to the central metal ion.
D. Light is absorbed when electrons move between d and s orbitals.
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17M.2.hl.TZ1.2f:
Outline why transition metals form coloured compounds.
- 19N.1.hl.TZ0.8: What is the effect of a stronger ligand?
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21M.2.hl.TZ2.2b(iv):
[Cr(OH)6]3− forms a green solution. Estimate a wavelength of light absorbed by this complex, using section 17 of the data booklet.
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22M.2.hl.TZ1.4e:
Mg(OH)+ is a complex ion, but Mg is not regarded as a transition metal. Contrast Mg with manganese, Mn, in terms of one characteristic chemical property of transition metals, other than complex ion formation.
- 21M.2.hl.TZ1.3g: Transition metals like iron can form complex ions. Discuss the bonding between transition...
- 21M.1.hl.TZ2.8: Which factor does not affect the colour of a complex ion? A. temperature of the...
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19M.2.hl.TZ1.6b:
Explain why, when ligands bond to the iron ion causing the d-orbitals to split, the complex is coloured.
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21M.2.hl.TZ2.2b(iii):
Deduce, giving a reason, which complex ion [Cr(CN)6]3− or [Cr(OH)6]3− absorbs higher energy light. Use section 15 of the data booklet.
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20N.2.hl.TZ0.6b:
The electron configuration of copper makes it a useful metal.
Explain why a copper(II) solution is blue, using section 17 of the data booklet.
- 22M.2.hl.TZ2.7d: Explain why transition metal cyanide complexes are coloured.
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21N.2.hl.TZ0.9b(iii):
Copper is a transition metal that forms different coloured complexes. A complex [Cu(H2O)6]2+ (aq) changes colour when excess Cl− (aq) is added.
Explain the cause of this colour change, using sections 3 and 15 from the data booklet.
