| Date | May 2018 | Marks available | 2 | Reference code | 18M.3.hl.TZ2.18 |
| Level | HL | Paper | 3 | Time zone | TZ2 |
| Command term | Identify and Draw | Question number | 18 | Adapted from | N/A |
Question
The conductivity of a germanium semiconductor can be increased by doping.
A dye-sensitized solar cell uses a ruthenium(II)–polypyridine complex as the dye. Two ruthenium(II) complexes, A and B, absorb light of wavelengths 665 nm and 675 nm respectively.
Draw the Lewis (electron dot) structure for an appropriate doping element in the box in the centre identifying the type of semiconductor formed.
State the feature of the molecules responsible for the absorption of light.
Outline why complex B absorbs light of longer wavelength than complex A.
Markscheme
ALTERNATIVE 1
B/Ga in circle AND Type of semiconductor: p-type
showing 3 electron pairs AND one lone electron «and hole»
ALTERNATIVE 2
P/As in circle AND Type of semiconductor: n-type
showing 4 electron pairs AND one non-bonded electron
Accept any group 13 element labelled as p-type.
Accept showing 7 electrons.
Accept any group 15 element labelled as n-type.
Accept showing 9 electrons.
Accept dots or crosses for electrons.
[2 marks]
conjugated C=C/carbon–carbon double bonds
OR
«multiple» alternating C=C/carbon–carbon double bonds
OR
«extensive electron» conjugation/delocalization
OR
«many» fused/conjugated aromatic/benzene rings
[1 mark]
complex B has greater conjugation/delocalization
[1 mark]
Examiners report
Syllabus sections
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18M.3.hl.TZ2.18b.ii:
Outline why complex B absorbs light of longer wavelength than complex A.
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18M.3.hl.TZ2.18b.i:
State the feature of the molecules responsible for the absorption of light.
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18M.3.hl.TZ1.15c:
The structure of two dyes used in DSSCs are shown.
Predict, giving a reason, which dye will absorb light of longer wavelength.
- 18N.3.hl.TZ0.15d.ii: Outline the effect of sunlight on the dye in the solar cell.
- 18N.3.hl.TZ0.15d.iii: State the purpose of TiO2.
- 18N.3.hl.TZ0.15d.i: Identify the structural feature of the dye that allows the conversion of solar energy into...
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18N.3.hl.TZ0.15d.iv:
Deduce the reduction half-equation at the cathode.
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17M.3.hl.TZ2.18a.ii:
The structures of 11-cis-retinal and β-carotene are given in section 35 of the data booklet. Suggest a possible wavelength of light absorbed by each molecule using section 3 of the data booklet.
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17M.3.hl.TZ1.19b:
Both photosynthesis and the Grätzel cell use energy from sunlight to bring about reduction. Deduce an equation for the reduction reaction in the electrolyte of a Grätzel cell.
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17M.3.hl.TZ2.19a:
Contrast how absorption of photons and charge separation occur in each device.
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17N.3.hl.TZ0.19b:
The natural absorption of light by chlorophyll has been copied by those developing dye-sensitized solar cells (DSSCs). Outline how a DSSC works.
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19M.3.hl.TZ1.18a:
Some solar cells use photovoltaic semi-conductors. Compare, giving reasons, the electrical conductivity of metals and semi-conductors as temperature increases.
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19M.3.hl.TZ2.20a:
Sketch graphs to show the general effect of increasing temperature on the electrical conductivity of semiconductors and metals on the axes below.
- 19N.3.hl.TZ0.20d(ii): Suggest an advantage of the DSSC over silicon-based photovoltaic cells.
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19M.3.hl.TZ1.18b:
Suggest one advantage of a dye-sensitized solar cell (DSSC) over a silicon based photovoltaic cell.
- 19N.3.hl.TZ0.20d(i): Outline the functions of the dye, TiO2 and the electrolyte in the operation of the...
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18M.3.hl.TZ1.15a:
Early photovoltaic cells were based on silicon containing traces of other elements. State the type of semiconductor produced by doping silicon with indium, In, giving a reason that refers to its electronic structure.
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19M.3.hl.TZ2.20b:
Explain the function of dyes in a dye-sensitized solar cell (DSSC).
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16N.3.hl.TZ0.21c:
Dye-sensitized solar cells (DSSC) convert solar energy into electrical energy.
(i) Describe how a DSSC converts sunlight into electrical energy.
(ii) Explain the role of the electrolyte solution containing iodide ions, I−, and triiodide ions, I3−, in the DSSC.
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17M.3.hl.TZ2.19b:
Suggest one advantage a DSSC has over a silicon based photovoltaic cell.
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18M.3.hl.TZ1.15b:
Dye-sensitized solar cells, DSSCs, use a dye to absorb the sunlight. State two advantages that DSSCs have over traditional silicon based photovoltaic cells.
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17M.3.hl.TZ1.19a:
Identify two ways in which the structure of the dye shown resembles the chlorophyll molecule. Use section 35 of the data booklet.
- 20N.3.hl.TZ0.14b: Doping of silicon increases the conductivity in semiconductors. Explain how doping improves...
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20N.3.hl.TZ0.14a:
Doping of silicon increases the conductivity in semiconductors.
Describe the doping in p-type and n-type semiconductors.
