Titanium dioxide exists as both bulk material and as nanoparticles. Explain why titanium dioxide nanoparticles are more effective as a catalyst than the same mass of bulk titanium dioxide.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Titanium dioxide is a white solid used as a pigment in paints. Scientists are investigating its use as a catalyst in industrial reactions. Nanoparticles of titanium dioxide have a diameter of around 20 nm.
Model answer (4 marks)
Titanium dioxide nanoparticles have a much larger surface area to volume ratio than bulk titanium dioxide. For the same mass, a larger proportion of atoms are exposed on the surface of the nanoparticles. Consequently more active sites are available for reactant molecules to adsorb and react. This increases the rate of the catalysed reaction, making the catalyst more efficient.
Examiner tips
- Use the term "surface area to volume ratio" to justify the size effect
- Explain that a higher surface area gives more exposed atoms/active sites
- Show the link between more active sites and a higher reaction rate
- Use the word "efficient" to summarise the effect
Common mistakes
- Confusing bulk and nanoparticle properties, e.g. saying bulk has more surface area
- Failing to mention the increased number of exposed atoms or active sites
- Using vague phrases like "smaller particles" without explaining the surface area effect
Mark scheme (4 marks)
- Nanoparticles have a much larger surface area to volume ratio than bulk titanium dioxide
- Because more atoms/particles are exposed on the surface (for the same mass)
- More active sites are available for reactant molecules to interact with
- Therefore the rate of the catalysed reaction is increased / the catalyst works more efficiently
Key terms in this question
nanoparticles · catalyst · bulk
Related
- All Edexcel GCSE Chemistry (1CH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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