Structure and Properties — NanoparticlesAQA GCSE Chemistry: Subtopic test

1. 1
   A sun cream manufacturer replaces the large particles of titanium dioxide used in an older formula with nanoparticles of titanium dioxide of the same total mass, giving a transparent cream instead of a thick white paste. Some customers ask whether the smaller particles are safe to use on skin.

   (a)

   What is the main reason nanoparticles behave differently from the same substance in bulk form?

   [1 mark]

   • ANanoparticles have a smaller surface area to volume ratio than bulk particles
   • BNanoparticles contain completely different atoms from the bulk material
   • CNanoparticles have a much larger surface area to volume ratio than bulk particles
   • DNanoparticles are chemically unreactive compared with bulk particles

   (b)

   Which of these is a genuine concern that scientists have investigated regarding the use of nanoparticles such as titanium dioxide in sun creams applied to human skin?

   [1 mark]

   • AWhether the small nanoparticles could penetrate skin or cells and cause unknown health effects
   • BWhether the nanoparticles will change into a different element once applied to skin
   • CWhether the nanoparticles will make the cream heavier to carry
   • DWhether the nanoparticles will become radioactive after contact with sunlight

   (c)

   Evaluate one advantage and one possible risk of the manufacturer's decision to use titanium dioxide nanoparticles instead of bulk titanium dioxide in its sun cream.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An industrial chemist develops a new catalyst for a factory reaction by using platinum nanoparticles spread across a support material, instead of a solid block of platinum of the same mass. This change allows the factory to use far less platinum overall while achieving the same rate of production.

   (a)

   Why does this change typically make the catalyst more effective at speeding up the reaction?

   [1 mark]

   • AThe nanoparticles change the platinum into a completely different element with new catalytic properties
   • BThe nanoparticles have a lower surface area to volume ratio, concentrating the reaction in a smaller space
   • CThe nanoparticles provide a much greater surface area for reactant particles to collide with per gram of platinum used
   • DThe nanoparticles increase the mass of platinum needed for the same reaction rate

   (b)

   The factory finds that switching to platinum nanoparticle catalysts allows them to use far less platinum overall while achieving the same rate of production. Which of the following best explains a likely economic benefit of this change for the factory?

   [1 mark]

   • APlatinum nanoparticles react completely and are used up, so they never need replacing
   • BNanoparticles of platinum are always cheaper to buy in total than a small solid block of the same substance
   • CUsing nanoparticles removes the need for the factory to purchase any catalyst at all
   • DPlatinum is an expensive metal, so using less of it for the same catalytic effect reduces production costs

   (c)

   Explain, in terms of surface area to volume ratio, why spreading a small mass of platinum as nanoparticles across a support material provides a similar catalytic effect to using a much larger mass of platinum as a solid block.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A cosmetics researcher is comparing silver nanoparticles used as an antibacterial ingredient in a deodorant with ordinary bulk silver metal. She must decide whether to recommend the nanoparticle form for a new product line, considering both performance and safety information supplied by two separate laboratory studies.

   (a)

   Describe how the particle size range that defines a nanoparticle differs from that of particles in bulk material, and explain why the nanoparticle form is more effective at killing bacteria for the same mass of silver used.

   [3 marks]

   (b)

   One laboratory study reports that silver nanoparticles from deodorants can wash off skin during showering and enter waterways, where they may affect the growth of naturally occurring bacteria in rivers. A second laboratory study finds no measurable harm to human skin cells from typical deodorant exposure levels. Using this information, evaluate whether the researcher should recommend using silver nanoparticles in the new deodorant product.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An electronics company is developing a new generation of highly sensitive medical diagnostic sensors that use gold nanoparticles to detect very small amounts of a disease marker in a patient's blood sample, aiming to allow diseases to be diagnosed earlier than with existing bulk-gold sensors.

   (a)

   Using ideas about nanoparticle structure and surface area to volume ratio, explain fully how using gold nanoparticles rather than bulk gold could make the sensor far more sensitive, and outline what further safety and cost information the company would need before bringing such a sensor to market.

   [6 marks]

   (b)

   A regulatory body reviewing the new gold nanoparticle sensor asks the electronics company to justify why nanoparticles were chosen over other possible approaches, such as simply using a larger sample of blood with a conventional bulk-gold sensor to detect the same disease marker. Evaluate the scientific and practical case for using gold nanoparticles rather than increasing the sample size with bulk-gold technology.

   [6 marks]

   Total for question 4: 12 marks

End of questions