Bulk and Surface Properties of Matter Including Nanoparticles

1. Nanoparticles are defined as particles with diameters between 1 and 100 nm. Write this range of diameters in metres in standard form.

Answer: 1 × 10−9 m  and  1 × 10−7 m

2. A cubic nanoparticle of zinc oxide has sides that are 15 nm long. Calculate the surface area to volume ratio of this nanoparticle.

Answer: The total surface area is 15 nm × 15 nm × 6 = 1350 nm2. The volume is (15 nm)3 = 3375 nm3. The surface area to volume ratio of this nanoparticle is 1350 : 3375  = 0.4

3. Give three uses of nanoparticles.

Answer: in fuel cells, medicine, sun cream, cosmetics, clothing, deodorants, electronics 

4. Silver nanoparticles are used in clothing due to their anti-bacterial properties. Using coarse particles of silver in clothing is not effective in killing the bacteria that cause unpleasant odours.

a) Explain why silver nanoparticles have different properties from those of larger silver particles.

Answer: Nanoparticles are very small so have very high surface area to volume ratios compared with larger particles (this means that a much higher fraction of atoms are at the surface of the nanoparticle, and this gives the nanoparticles different properties).

b) Explain why adding silver nanoparticles to clothing does not increase the cost of the clothing significantly.

Answer: Due to the high surface area to volume ratio, only small amounts of silver nanoparticles are necessary to be effective.

c) The diameter of a silver atom is 1.7 × 10−10 m. Calculate the number of silver atoms that fit side-by-side along the edge of a 20 nm wide silver nanoparticle. Give your answer to the nearest whole number.

Answer: Diameter of Ag atom is 0.17 nm. The number of Ag atoms is 20 nm ÷ 0.17 nm = 117.6 atoms = 118 atoms

d) As a bulk material silver is an unreactive metal that has no known risks to human health. Suggest why some people are concerned about the possible health effects of using silver nanoparticles in clothing.

Answer: Because nanoparticles have different properties to those of the bulk material it is not safe to assume that they are harmless. Silver nanoparticles may be able to enter into cells and cause damage, unlike bulk silver.