2.10 Nanoparticles
5 exam questions worth 10 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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What is the size range of nanoparticles?
Choose one answer.
Correct Not quite: the answer is 1 to 100 nm
Mark scheme
B
Model answer
B: nanoparticles are 1 to 100 nm across.
A cube has sides of 3 cm.
Calculate its surface area to volume ratio.
Mark scheme
- surface area = 6 × 3 × 3 = 54 cm2 (1)
- volume = 3 × 3 × 3 = 27 cm3 (1)
- ratio = 54 : 27 = 2 (or 2 : 1) (1)
Model answer
Surface area = 54 cm2, volume = 27 cm3, so SA : V = 54 ÷ 27 = 2.
A cube of side 1 µm is cut into cubes of side 0.1 µm.
State how the surface area to volume ratio changes.
Mark scheme
- it increases by a factor of 10 / is 10 times bigger (1)
Model answer
The side decreases by a factor of 10, so the surface area to volume ratio increases by a factor of 10.
Explain why nanoparticles of platinum make better catalysts than the same mass of platinum powder.
Mark scheme
- nanoparticles have a much higher surface area to volume ratio (1)
- more atoms exposed for the reaction / less catalyst needed (1)
Model answer
Nanoparticles have a much higher surface area to volume ratio, so more of the catalyst is exposed to the reactants and less is needed.
Some sun creams contain nanoparticles of titanium dioxide.
Give one advantage and two possible risks of using these sun creams.
Mark scheme
- advantage: block UV light / better skin coverage / transparent so not visible on skin (1)
- risk: may be absorbed into the body / enter cells (1)
- risk: may be toxic / damage cells / harm the environment / long-term effects unknown (1)
Model answer
The nanoparticles give good protection from UV and are invisible on the skin. However, they could be absorbed through the skin into cells, and their long-term effects on health and on the environment are not yet known.
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