Investigating osmosis
Investigating the water potential of potato using the weighing method.
INTRODUCTION
When the potato is immersed in a solution where there is no change in mass, there is no net
flow of water into or from the cells by osmosis, i.e. the rate at which water enters the cells =
the rate at which water enters the cells.
At this point, CELL = BATHING SOLUTION
Before you start work:
• Read all instructions carefully.
• Write an equipment list from the method below
• Write a risk assessment and safety precautions
• Prepare a suitable table to record your data.
Method:
a) Sucrose solution preparation.
From the 1 mole stock solution of sucrose, prepare 10 cm3 of each of the required
solutions: 0.2, 0.4, 0.6, and 0.8 mole.
Concentration of sucrose solution (M)
0 0.2 0.4 0.6 0.8 1.0
Volume of 1.0 M sucrose solution added (cm3) 0 2 4 6 8 10
Volume of distilled water added cm3) 10 8 6 4 2 0

Method – Procedure
1. Label six test tubes / boiling tubes with the concentration of Sucrose solution to be
used.
2. Fill the tubes with 10 ml of the prepared sucrose solution at the correct concentration.
3. Cut 6 potato pieces to the size secified and dry them on a paper towel
4. Weigh the potato pieces using a balance and record masses in an appropriately
designed table.
5. Place potato pieces in a beaker/ boiling tube. The solutions should completely cover
the chips.
6. Leave for 30 minutes.
7. Remove potato pieces one at a time from the beakers/ boiling tubes.
8. Dry the potato pieces on paper towel.
9. Reweigh potato pieces and record results in the table.
10. Repeat instructions for steps 3 to 11, using the other concentrations of Sucrose
solutions.
11. Record and keep your results securely.
12. Calculate the change in mass and the percentage change in mass of each set of
potato pieces.
13. Plot percentage change in mass (y–axis) against concentration of Sucrose solution (x–
axis).
14. Calculate the percentage change in mass using the formula below:
% change in mass = final mass – initial mass x 100%
Initial mass
14. Where there is no net gain or loss in mass, CELL is equal to BATHING SOLUTION. From
your graph read the molarity of sucrose where the percentage mass change is zero.
15. From the table below, find the water potential of a sucrose solution of that
molarity

Page 4 of 4
Table showing the water potential of solutions of different molarity
Molarity/mol dm–3 Water potential/kPa
0.05 –130
0.10 –260
0.15 –410
0.20 –540
0.25 –680
0.30 –860
0.35 –970
0.40 –1120
0.45 –1280
0.50 –1450
0.55 –1620
0.60 –1800
0.65 –1980
0.70 –2180
0.75 –2370
0.80 –2580
0.85 –2790
0.90 –3000
0.95 –3250
1.00 –350