1. 1
   A cosmetics company adds titanium dioxide nanoparticles, each between 1 and 100 nm in size, to a sunscreen. Unlike bulk titanium dioxide, which appears as a thick white paste, the nanoparticle version spreads on the skin as a transparent layer, while still absorbing harmful UV rays effectively.

   (a)

   Which statement describes what defines a nanoparticle such as this one?

   [1 mark]

   • AA particle containing millions of atoms arranged in a giant lattice structure
   • BA particle with a size of roughly 1 to 100 micrometres, visible under a standard light microscope
   • CA particle with a size of roughly 1 to 100 nanometres, made up of only a few hundred atoms
   • DAny particle that is white in colour and used in cosmetics

   (b)

   The nanoparticle sunscreen absorbs UV rays just as effectively as the bulk material, while using a much smaller mass of titanium dioxide. Which statement explains why nanoparticles can be so effective in smaller amounts?

   [1 mark]

   • ANanoparticles absorb UV rays only because they are white in colour
   • BNanoparticles contain more titanium atoms per particle than bulk titanium dioxide
   • CNanoparticles are chemically different elements from bulk titanium dioxide
   • DNanoparticles have a very high surface area to volume ratio, so a much greater proportion of their atoms are exposed at the surface, where they can interact with UV rays

   (c)

   Explain, in terms of particle size and surface area to volume ratio, why titanium dioxide nanoparticles can be used more efficiently than bulk titanium dioxide in sunscreen.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A car manufacturer uses platinum nanoparticles, rather than bulk platinum, as the catalyst inside a catalytic converter, which speeds up reactions that reduce harmful exhaust gases. A government health agency is also reviewing the safety of nanoparticles used in consumer products, since their properties can differ from the bulk material.

   (a)

   Which statement explains why using nanoparticles allows the manufacturer to use much less platinum than bulk platinum would require?

   [1 mark]

   • APlatinum nanoparticles are magnetic, which attracts exhaust gases towards them
   • BPlatinum nanoparticles react chemically to form a completely new element inside the converter
   • CNanoparticles have a much higher surface area to volume ratio than bulk platinum, providing many more sites for the exhaust gas molecules to react on, using less material for the same effect
   • DNanoparticles of platinum are cheaper to produce than bulk platinum of the same total mass

   (b)

   A government health agency is also reviewing the safety of nanoparticles used in consumer products, since their properties can differ from the bulk material. Which statement describes a genuine concern that health agencies have raised about nanoparticles?

   [1 mark]

   • ANanoparticles always have identical properties and risks to the bulk form of the same substance
   • BNanoparticles are known to be completely safe in all circumstances, with no research needed
   • CNanoparticles cannot be absorbed by the human body under any circumstances
   • DBecause nanoparticles are so small, they may be able to enter the human body more easily than larger particles, and their long-term health effects are not yet fully understood

   (c)

   Explain why using platinum nanoparticles as a catalyst reduces the amount of platinum needed, and explain why health agencies are still cautious about the widespread use of nanoparticles in consumer products.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A textile company adds silver nanoparticles to sports socks because silver nanoparticles kill bacteria that cause odour, more effectively per gram than bulk silver. Environmental scientists are studying what happens to these silver nanoparticles after the socks are washed and the water enters rivers.

   (a)

   Explain, in terms of surface area to volume ratio, why silver nanoparticles are more effective at killing bacteria than the same mass of bulk silver.

   [3 marks]

   (b)

   Environmental scientists are studying what happens to the silver nanoparticles after the socks are washed and the water enters rivers, since nanoparticles may behave differently from bulk silver once released into the environment. Explain why scientists are concerned about the environmental effects of silver nanoparticles entering rivers, referring to their size and reactivity.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A technology company is developing a new gas sensor that uses metal oxide nanoparticles to detect extremely low concentrations of a toxic gas in a factory, far more sensitively than sensors made from the bulk metal oxide. Before releasing the sensor, the company must also evaluate the potential risks of manufacturing large quantities of these nanoparticles.

   (a)

   Describe, in terms of the structure and properties of nanoparticles, how using nanoparticles could make this sensor more sensitive than one made from the bulk material.

   [6 marks]

   (b)

   Before releasing the sensor, the company must also evaluate the potential risks of manufacturing large quantities of these nanoparticles. Evaluate the benefits and potential risks of using nanoparticles in this new gas sensor, referring to their properties and to the current state of scientific understanding about nanoparticle safety.

   [6 marks]

   Total for question 4: 12 marks

End of questions