A student carries out an experiment to investigate how concentration affects the rate of diffusion using dialysis tubing (Visking tubing) as a model of a cell membrane. The student fills a length of dialysis tubing with glucose solution and submerges it in a beaker of distilled water.
The diagram shows the experimental setup:
The student repeats the experiment using five different initial concentrations of glucose solution inside the dialysis tubing, each for a duration of 30 minutes. For each concentration, the experiment is carried out three times, and the final concentration of glucose in the surrounding water is measured in mmol/dm3\text{mmol/dm}^3mmol/dm3.
The results are shown in the table below:
| Initial concentration of glucose inside tubing (mol/dm³) | Glucose concentration in beaker after 30 mins: Trial 1 (mmol/dm³) | Glucose concentration in beaker after 30 mins: Trial 2 (mmol/dm³) | Glucose concentration in beaker after 30 mins: Trial 3 (mmol/dm³) | Mean glucose concentration in beaker (mmol/dm³) |
|---|---|---|---|---|
| 0.2 | 1.2 | 1.1 | 1.3 | 1.2 |
| 0.4 | 2.3 | 2.5 | 2.4 | 2.4 |
| 0.6 | 3.4 | 3.9 | 3.5 | ? |
| 0.8 | 4.6 | 4.8 | 4.7 | 4.7 |
| 1.0 | 5.6 | 5.9 | 5.6 | 5.7 |
Describe what is meant by the term diffusion.
Calculate the mean glucose concentration in the beaker for the 0.6 mol/dm³ initial concentration.
Describe the effect of the initial glucose concentration on the rate of diffusion.
Explain the relationship between initial glucose concentration and the rate of diffusion.
State two variables that the student should control in this experiment to ensure that the results are valid.