1. 1
   A cosmetics company reformulates one of its sunscreens. The original sunscreen contains titanium dioxide particles with a diameter of 4000 nm, which give the cream a visible white appearance on the skin. The reformulated sunscreen contains titanium dioxide nanoparticles with a diameter of 40 nm, which make the cream transparent on the skin while still absorbing ultraviolet light. Both sunscreens contain the same total mass of titanium dioxide per bottle.

   (a)

   A cosmetics company produces a sunscreen containing titanium dioxide particles that are 40 nm in diameter, compared with an older sunscreen containing titanium dioxide particles that are 4000 nm in diameter. What is the diameter, in metres, of the 40 nm particle?

   [1 mark]

   • A4.0 $\times$ 10^{-8} $\text{ m}$
   • B4.0 $\times$ 10^{-7} $\text{ m}$
   • C4.0 $\times$ 10^{-6} $\text{ m}$
   • D4.0 $\times$ 10^{-5} $\text{ m}$

   (b)

   Compared with the original sunscreen, why is the reformulated nanoparticle sunscreen more effective at absorbing ultraviolet light for the same mass of titanium dioxide used?

   [1 mark]

   • AThe nanoparticles have a lower melting point than the larger particles
   • BThe nanoparticles have a much greater surface area to volume ratio than the larger particles
   • CThe nanoparticles contain fewer titanium and oxygen atoms than the larger particles
   • DThe nanoparticles have a different chemical formula from the larger particles

   (c)

   Give one possible risk to human health of using nanoparticulate materials such as titanium dioxide in sunscreens, and explain why this risk exists.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A materials science technician is comparing three samples of the same metal oxide powder: sample X consists of fine particles (PM2.5), sample Y consists of nanoparticles, and sample Z consists of ordinary bulk particles several millimetres across. The technician measures the diameter of a typical particle in each sample and records the surface area to volume ratio for each.

   (a)

   Which of these best describes the size range of nanoparticles?

   [1 mark]

   • A1–100 pm in diameter
   • B1–100 $\text{ }\mu\text{m} \text{ in diameter}$
   • C1–100 mm in diameter
   • D1–100 nm in diameter

   (b)

   The technician finds that sample Y has a much higher surface area to volume ratio than sample Z, even though both samples contain the same total mass of the metal oxide. What is the best explanation for this observation?

   [1 mark]

   • ASample Y contains a different chemical compound from sample Z
   • BSample Y particles have a lower density than sample Z particles
   • CAs particle size decreases, the ratio of surface area to volume increases
   • DAs particle size decreases, the ratio of surface area to volume decreases

   (c)

   Explain, using surface area to volume ratio, why converting sample Z (bulk particles) into sample Y (nanoparticles) could increase the effectiveness of the metal oxide as a catalyst.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A construction company is choosing a material for the outer cladding panels of a new building. They compare four candidate materials: soda-lime glass, a thermosetting polymer, a glass-fibre reinforced composite, and an aluminium alloy. Data supplied by the manufacturers shows: soda-lime glass is very stiff but shatters under a sudden impact; the thermosetting polymer resists cracking but softens above 150 degrees Celsius; the glass-fibre composite combines high strength with low weight but is difficult to recycle; the aluminium alloy is strong, lightweight and can be recycled repeatedly, but conducts heat readily.

   (a)

   Using the data given, explain which single material would be most suitable for the cladding panels, considering strength, durability and safety in the event of a fire.

   [3 marks]

   (b)

   The company also considers using clay ceramic tiles as an alternative to soda-lime glass panels for a decorative, non-structural section of the cladding. Using the properties described, explain two reasons why clay ceramic tiles would be more suitable than soda-lime glass for this decorative section, and one limitation of using clay ceramic tiles compared with the glass-fibre composite.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Silver nanoparticles are increasingly added to textiles, wound dressings and food packaging because of their antibacterial properties, since silver ions released from the nanoparticles kill many types of bacteria. However, some environmental scientists have raised concerns that washing textiles containing silver nanoparticles releases them into wastewater, where they may enter rivers and affect aquatic ecosystems, while some toxicologists note that the long-term effects of nanoparticles on human health are not yet fully understood. A regulator is considering whether products containing nanoparticles should be labelled.

   (a)

   Discuss the benefits and possible risks of using silver nanoparticles in consumer products such as wound dressings and textiles, referring to their small size and large surface area to volume ratio in your answer.

   [6 marks]

   (b)

   A regulator is deciding whether to require manufacturers to label all consumer products that contain nanoparticles, so that customers can choose whether to buy them. Evaluate the case for and against introducing mandatory nanoparticle labelling on products such as wound dressings, textiles and food packaging, using ideas about the risks and uses of nanoparticulate materials.

   [6 marks]

   Total for question 4: 12 marks

End of questions