A water-treatment plant is testing two forms of the same solid. The pollutant is removed when it interacts with the exposed surface of the solid.
The particles of both forms are cubes. Each form was tested using a 1.0 dm3 sample of polluted water with the same starting concentration. Both forms removed 95% of the pollutant.
| Form | Side length of each particle in nm | Mass used in g | Cost in p per g | Particle mass recovered after treatment in % |
|---|---|---|---|---|
| S | 20 | 0.50 | 14 | 80 |
| L | 200 | 5.0 | 2.0 | 99 |
Particles that are not recovered remain in the treated water. This water would be discharged into a river. The effects of both forms of particle on organisms in the river are uncertain.
Calculate how many times greater the surface area to volume ratio of form S is than the surface area to volume ratio of form L.
A third form, T, is made of cubic particles with a side length of 10 nm10\ \text{nm}10 nm.
Assume that the mass needed to remove 95% of the pollutant is inversely proportional to the surface area to volume ratio.
Use your answer to part (a) and the data in the table to calculate the mass of form T needed.
Evaluate whether the treatment plant should use form S rather than form L.
Use calculations in your answer.
104 exam-style questions on AQA GCSE Chemistry 2.4 Bulk and surface properties of matter including nanoparticles, covering 2.4.1 Sizes of particles and their properties and 2.4.2 Uses of nanoparticles. Each one has a worked solution and a mark scheme showing where the marks go.