Diffusion is the movement of particles from a high to lower concentration. Osmosis is the diffusion of water across a membrane. Active transport moves particles from low to higher concentration.

For a potato cylinder placed in distilled water with a sucrose concentration of 0 mol dm^{−3} the following results were obtained.

Concentration of sucrose % | Mass of potato cylinder at start (g) | Mass of potato cylinder at end (g) | Change in mass (g) |
---|---|---|---|

0 | 2.22 | 2.52 | +0.30 |

The increase in mass is the result of water being taken up by osmosis.

In this experiment, 0.30 grams of water were taken up by the potato cylinder.

This took place over 20 minutes, so the water uptake in an hour, assuming that the rate was constant, would be:

The rate of water uptake is therefore 0.90 g h^{−1}.

There is some variation in mass between the potato cylinders at the beginning of the experiment as it would be impractical to prepare the cylinders so that they were identical in mass.

So that we can compare changes in mass of different potato cylinders, it is necessary to calculate the percentage change in mass.

Some of the values we obtain for percentage change in mass will be positive, some will be negative.

For the potato cylinder in the distilled water:

The changes in mass, as percentages, must be calculated for each potato cylinder.

- Question
For the potato cylinder placed in a sucrose concentration of 0.2 mol dm

^{−3}, the following results were obtained:Concentration of sucrose % Mass of potato cylinder at start (g) Mass of potato cylinder at end (g) 0 2.42 2.54 Calculate the change in mass as a percentage.