Question 23M.3.HL.TZ2.15
| Date | May 2023 | Marks available | [Maximum mark: 12] | Reference code | 23M.3.HL.TZ2.15 |
| Level | HL | Paper | 3 | Time zone | TZ2 |
| Command term | Determine, Explain, Identify, Outline, State, Suggest, Write | Question number | 15 | Adapted from | N/A |
Photosynthesis enables green plants to store energy from sunlight as glucose.
Write the equation for photosynthesis.
[1]
6CO2 (g) + 6H2O (l) → C6H12O6 (aq) + 6O2 (g) ✓
Identify the structural feature that allows chlorophyll to absorb light.
Use section 35 of the data booklet.
[1]
conjugated «electronic» structure/delocalized «pi» electrons/alternate «single and» double bonds ✓
Accept “many/delocalized double bonds”.
Do not accept “tetrapyrrole group” alone without reference to idea of conjugation.
Explain how photosynthesis is being employed to control global warming.
[2]
reduces/sequesters CO2/carbon dioxide «concentration from atmosphere» ✓
«planting» more plants/trees ✓
Do not accept “carbon capture” alone for M1.
Do not accept just “plants/trees” alone for M2.
Photovoltaic cells also convert sunlight into energy.
State the form of energy produced by photosynthesis and photovoltaic cells.
Photosynthesis: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Photovoltaic: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
[1]
Photosynthesis: chemical
AND
Photovoltaic: electrical ✓
Accept "electricity" for "electrical".
Explain how a silicon-based photovoltaic cell brings about this conversion.
[3]
Any three of:
n-type AND p-type «silicon layers»
OR
n-type doped with Gp 15 element/P AND p-type doped with Gp 13 element/B ✓
potential difference/charge separation created between layers of silicon ✓
«sunlight produces» free electrons that flow between layers «from p-type to n-type»
OR
«sunlight produces» positive holes that flow between layers «from n-type to p-type» ✓
«excess» electrons move "from n-type to p-type" through an external circuit ✓
Do not accept movement of electrons or holes in wrong direction for M3.
Glucose can be converted to ethanol through fermentation:
C6H12O6 (aq) → 2C2H5OH (aq) + 2CO2 (g)
Determine the energy efficiency of this conversion in terms of the enthalpies of combustion of the reactants and products. Use section 13 of the data booklet.
[1]
«(2x −1367 / −2803) × 100 =» 97.54 %
OR 2.46 % loss «in energy efficiency» ✓
Suggest one reason, other than energy density and specific energy, why ethanol may be considered a more useful fuel than glucose.
[1]
liquid
OR
easier ignition
OR
more volatile ✓
Accept “complete combustion more likely”“
OR
“better octane rating”
OR
“engine must be converted in order to use glucose”.
Do not accept “less viscous”.
Both ethanol and glucose can be used to generate energy through fuel cells.
Outline one way fuel cells differ from primary cells.
[1]
material provides energy in fuel cells
OR
fuel continually added in fuel cells ✓
Accept converse statement.
Do not accept “fuel cells are rechargeable and primary are not easily recharged”.
State one way to increase the maximum current of a voltaic cell.
[1]
reduce «internal» resistance ✓
Accept “increase surface area”
OR
“reduce separation of electrodes”
OR
“increase concentration of electrolyte/ion mobility/temperature”.