Method:
1) Label six boiling tubes 0.0, 0.2, 0.4, 0.6, 0.8, 1.0 mol dm^-3 sucrose.
2) Use the 1.0 mol dm^-3 sucrose solution and water to make up 20 cm cubed of sucrose solution of each of the concentrations for each labelled boiling tube.
3) Stand the boiling tubes containing the sucrose solutions in a water bath set at 30 degrees celsius. Use a thermometer to check the temperatures in all tubes reaches the room temperature at 30 degrees celsius.
4) Using the cork borer, cut six chips from your potato. Use a ruler, scalpel and tile to cut all of the chips to the same length. Blot the potato chips dry with a paper towel. Do not squeeze the chips.
5) Weigh each potato chip. Record these initial masses in a suitable table.
6) At the water bath, set the stop clock to zero. Quickly transfer each potato chip from its square of paper towel to its own boiling tube.
7) After 20 minutes, remove the chips from boiling tubes. Blot the chips dry, then reweigh them. Record the final masses in your table.
8) Calculate the change in mass and then calculate the percentage change in mass.
9) Plot a graph of your processed data (change in mass against concentration of sucrose solution). The point at which the line of best fit crosses the x axis (zero change in mass) indicates the point at which the solution is isotonic. This is when the water potential of sucrose solution is the same as the water potential of the potato tissue, so there is no net movement of water in or out of the potato.