A student carries out an experiment to investigate how concentration affects the rate of diffusion through a semi-permeable membrane.
The student places different concentrations of glucose solution into five separate visking tubing bags, which are then submerged in beakers containing 100 cm3 of distilled water.
After 30 minutes, the student measures the concentration of glucose that has diffused into the surrounding water. The experiment is performed using three separate setups for each concentration. The results are shown in the table below:
| Glucose concentration inside tubing (mol dm−3\text{mol dm}^{-3}mol dm−3) | Glucose concentration in external water in Trial 1 (mmol dm−3\text{mmol dm}^{-3}mmol dm−3) | Glucose concentration in external water in Trial 2 (mmol dm−3\text{mmol dm}^{-3}mmol dm−3) | Glucose concentration in external water in Trial 3 (mmol dm−3\text{mmol dm}^{-3}mmol dm−3) | Mean glucose concentration in external water (mmol dm−3\text{mmol dm}^{-3}mmol dm−3) |
|---|---|---|---|---|
| 0.2 | 1.15 | 1.25 | 1.20 | 1.20 |
| 0.4 | 2.35 | 2.45 | 2.40 | 2.40 |
| 0.6 | 3.52 | 3.65 | 3.57 | ? |
| 0.8 | 4.55 | 4.70 | 4.61 | 4.62 |
| 1.0 | 5.10 | 5.30 | 5.20 | 5.20 |
Describe what is meant by the term diffusion.
Calculate the average (mean) glucose concentration in the external water for the 0.6 mol dm-3 initial concentration.
Describe the effect of the initial glucose concentration inside the tubing 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.