What are nanoparticles, why does size matter so much, and how do we represent the states of substances?
Nanoparticles, coarse and fine particles, the high surface area to volume ratio of nanoparticles and its consequences, uses and risks of nanoparticles, and the state symbols used in equations.
A focused answer to OCR Gateway GCSE Chemistry A topic C2.2 on nanoparticles, covering the sizes of coarse, fine and nanoparticles, the surface area to volume ratio and why it matters, the uses and risks of nanoparticles, and the state symbols used in chemical equations.
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What this dot point is asking
OCR wants you to know what nanoparticles are, compare them with coarse and fine particles by size, explain the importance of the surface area to volume ratio, and discuss the uses and risks of nanoparticles. You also need the state symbols used in chemical equations, which describe the physical state of each substance in a reaction.
The sizes of particles
A nanometre is one billionth of a metre. Nanoparticles are so small they behave differently from the same material in larger pieces, which is why they have special properties.
Surface area to volume ratio
A useful rule: if the length of each side is divided by 10, the surface area to volume ratio is multiplied by 10. Because chemical reactions and catalysis happen at the surface, the large surface area to volume ratio of nanoparticles makes them very reactive per gram, so only a small mass is needed.
Uses of nanoparticles
The special properties of nanoparticles lead to many uses, for example:
- Catalysts: a huge surface area makes them very effective catalysts using little material.
- Sun creams: nanoparticles (such as titanium dioxide) give better protection from ultraviolet light and are not visible white on the skin.
- Antibacterial: silver nanoparticles kill bacteria, so they are used in wound dressings, socks and surface coatings.
- Electronics and medicine: they are used in tiny electronic components and to deliver drugs to specific cells.
Risks of nanoparticles
Because nanoparticles are so small and new, their risks are not fully understood. They could be breathed in or pass into cells and the bloodstream in ways larger particles cannot, and their long-term effects on health and the environment are uncertain. This is why their use is researched and, in some products, regulated or labelled.
State symbols
Exam-style practice questions
Practice questions written in the style of OCR exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
OCR 20184 marksA cube of a material has sides of 100 nm. Calculate its surface area to volume ratio, and explain why nanoparticles are much more reactive, per gram, than the same material in larger pieces.Show worked answer →
A Higher tier calculation and explanation. Reward: for a cube of side nm, the surface area is and the volume is , so the surface area to volume ratio is (or ). The explanation: as particles get smaller, a much greater proportion of their atoms are on the surface, so the surface area to volume ratio increases. Reactions and catalysis happen at the surface, so nanoparticles expose far more reactive surface per gram and are therefore much more reactive and effective as catalysts than the same mass of larger particles. Markers credit the surface area (), the volume (), the ratio, and the link between higher surface area to volume ratio and greater reactivity.
OCR 20214 marksNanoparticles of silver are added to wound dressings and socks. Give one property that makes silver nanoparticles useful for this, state one possible risk of using nanoparticles, and explain why such a small mass of nanoparticles can be effective.Show worked answer →
A C2.2 application question. Reward: silver nanoparticles have antibacterial (antimicrobial) properties, which is useful in dressings and socks to kill bacteria and reduce infection or odour. A possible risk is that, because nanoparticles are so small and have such large surface areas, their effects on health and the environment are not fully understood; they could be absorbed into the body or cells in ways larger particles are not, or have unknown long-term effects. A very small mass is effective because nanoparticles have a huge surface area to volume ratio, so even a tiny amount provides a large reactive surface. Markers credit a useful property (antibacterial), a sensible risk (uncertain health or environmental effects), and the large surface area to volume ratio explaining why little is needed.
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