Analysing results

The investigation cannot be based on changes in mass from just one potato cylinder.

curriculum-key-fact
In scientific tests, we must ensure a number of measurements are made to allow for uncertainty and error in data and anomalous results.

Percentage changes in mass must be calculated for each cylinder. A mean value for the change in mass of potato cylinders at each concentration - measured in moles of sucrose per dm3 of solution, or mol dm-3 - should be calculated.

A graph is plotted of change in mass, in per cent, against concentration of sucrose.

Where potato cylinders have gained in mass, the change will be positive.

Where potato cylinders have decreased in mass, the change will be negative.

Concentration of sucroseMean change in mass
0.0+26.8
0.2+5.0
0.4-7.7
0.6-17.9
0.8-26.0
1.0-31.4
A graph showing the change of mass and the concentration of sucrose.A graph showing the change of mass and the concentration of sucrose.

Where the plotted line crosses the horizontal axis at 0 per cent change in mass, the sucrose concentration is equal to the concentration of dissolved substances in the potato cells.

This can be identified on the graph as the point which shows no change in mass, and therefore represents no net movement of water by osmosis.

Question

What is the concentration of solutes in the cells of the potato in this investigation?

0.27 mol dm-3.

This value is where the line crosses the x-axis.