Elena investigated the effect of concentration of a solution on the rate of diffusion of gas. In a fume cupboard, she set up a horizontal glass tube with small squares of damp red litmus paper spaced at 8 cm intervals along its length. She added 3 drops of 2.0 M ammonia solution to some cotton wool and placed it at one end of the tube, closing it with a stopper. She timed how long it took for each square of litmus paper to turn blue.
She then repeated the experiment using an identical tube but with 3 drops of 5.0 M ammonia solution.
Her results are shown in the table:
| Concentration of ammonia solution | Time taken for litmus paper to change colour (seconds) | | :---: | :---: | :---: | :---: | :---: | :---: | :---: | | | 8 cm | 16 cm | 24 cm | 32 cm | 40 cm | 48 cm | | 2.0 M | 10 | 21 | 32 | 41 | 51 | 62 | | 5.0 M | 5 | 10 | 15 | 20 | 25 | 30 |
Describe what is meant by the term diffusion.
Calculate the average rate of diffusion, in centimeters per second (cm/s\text{cm/s}cm/s), of ammonia gas from the 5.0 M experiment between the litmus papers at 8 cm8\text{ cm}8 cm and 48 cm48\text{ cm}48 cm. Show your working.
Explain, in terms of particles, why the rate of diffusion is faster when 5.0 M ammonia solution is used compared to 2.0 M ammonia solution.