All topics › AQA GCSE Chemistry › Sizes of particles and their properties2.4.1 Sizes of particles and their propertiesAQA GCSE Chemistry (8462), Higher tier · Bonding, structure and the properties of matter › Nanoparticles
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Complete the sentence. surface area Sample questions Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1 Easy 4 marks
Nanoscience is the study of very small structures, such as nanoparticles.
(a) What size are nanoparticles?one box.[1]
1–100 nm 100–2500 nm 2500–10 000 nm more than 1 mm (b) What is 1 nm in metres?one box.[1]
1 × 10−3 m 1 × 10−6 m 1 × 10−9 m 1 × 10−12 m (c) Complete the sentence.[1]
(d) How do fine particles (PM2.5 ) compare in size with nanoparticles?one box.[1]
They are larger. They are smaller. They are the same size. They are single atoms. Show the answer and mark scheme (a) Answer: 1–100 nm
(b) Answer: 1 × 10−9 m
(d) Answer: They are larger.
Question 2 Medium 6 marks
A nanoparticle is a cube with sides of length 20 nm.
(a) Calculate the surface area of the cube.[1]
(b) Calculate the volume of the cube.[1]
(c) Calculate the surface area to volume ratio of the cube.[1]
(d) The length of the side of a cube is decreased by a factor of 10.[1]
(e) Explain why nanoparticles of a catalyst can be more effective than larger particles of the same catalyst.[2]
Show the answer and mark scheme (a) Answer: 2400 nm
2 (6 × 20 × 20 =) 2400 (nm2 ) (b) Answer: 8000 nm
3 (20 × 20 × 20 =) 8000 (nm3 ) (c) Answer: 0.3 nm
−1 (0.3 : 1)
(2400 ÷ 8000 =) 0.3 (nm−1 ) (d) Answer: It increases by a factor of 10.
it increases by a factor of 10 / becomes 10 times larger (e) Answer: They have a much larger surface area to volume ratio, so more of the catalyst is exposed and smaller quantities are needed.
nanoparticles have a larger surface area to volume ratio / more of their atoms are at the surface so smaller quantities are needed / more reacting particles can collide with the surface at once Question 3 Hard 7 marks
A silver nanoparticle is a sphere with a diameter of 40 nm.
(a) Calculate the surface area to volume ratio of the nanoparticle. Give your answer in nm−1 .[3]
(b) Show that a silver particle with a diameter of 40 µm has a surface area to volume ratio 1000 times smaller than that of the nanoparticle.[2]
(c) Silver nanoparticles are used to kill bacteria.[2]
Show the answer and mark scheme (a) Answer: 0.15 nm
−1 r = 20 nm: surface area = 4 × π × 202 = 5030 (nm2 ) volume = \(\frac{4}{3}\) × π × 203 = 33 500 (nm3 ) ratio = 0.15 (nm−1 ) (b) Answer: 40 µm = 40 000 nm, so the radius is 1000 times larger; the ratio (3 ÷ r) is 1000 times smaller: 0.000 15 nm
−1 .
40 µm = 40 000 nm so the radius is 1000 times larger / r = 20 000 nm ratio = 3 ÷ r (inversely proportional to r) so it is 0.15 ÷ 1000 = 0.000 15 (nm−1 ) (c) Answer: Nanoparticles have a much higher surface area to volume ratio, so more silver atoms are at the surface per gram and can act on bacteria.
higher surface area to volume ratio / more silver atoms at the surface per gram so the same effect is produced by a smaller quantity Related subtopics
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