Explain5 marksStandard
A student investigated the effect of surface area to volume ratio on the rate of diffusion. She prepared colourless agar blocks containing a pH indicator. She cut cubes of different sizes and placed each into a beaker of dilute hydrochloric acid. The acid diffuses into the agar and causes a colour change from purple to yellow. The time taken for the acid to diffuse completely through the cube (turning the entire cube yellow) was recorded.
| Cube side length (mm) | Surface area (mm²) | Volume (mm³) | SA:V ratio | Time for complete colour change (s) |
|---|---|---|---|---|
| 5 | 150 | 125 | 1.2 | 120 |
| 10 | 600 | 1000 | 0.6 | 480 |
| 20 | 2400 | 8000 | 0.3 | 1920 |
Explain the relationship between the size of the agar cube and the time taken for the acid to diffuse completely through the cube.