Investigating Osmosis

Question 1

Control variables

Answer 1

Type and volume of solute in solution, temperature and time

Question 2

Method

Answer 2

1) Use a cork borer to cut 5 potato cylinders of the same diameter.
2)Use a scalpel and ruler to trim each potato cylinder so they’re all the same length.
3)Measure the mass of each potato cylinder, in a top pan balance accurate to 0.01g and record in a table of results, recording the initial length(MM) of the potato cylinders in a similar table.
4)Measure 10cm3 of each sugar or salt solution and pour into each boiling tube. Label each boiling tube clearly, with at least one solution distilled water. Five different concentrations should he used.
5)Add one potato cylinder to each boiling tube and leave for a specified amount of time.
6)After a set time, remove the potatoes, blot dry and record the final mass and length of each potato.
7)Measure the percentage change in the mass and length of each plant tissue.

Question 3

Independent variable

Answer 3

Concentration of salt or sucrose solution in mol dm3

Question 4

Conclusion

Answer 4

A positive percentage change in mass indicates the potato’s gained water by osmosis meaning the solution’s more dilute, a negative percentage change suggests the opposite.

Question 5

Risks

Answer 5

Place the potato on a ceramic tile using the cork borer - don’t cut the potato cylinder towards your hand.
Take care when using the scalpel.

Question 6

How to improve the validity of the experiment

Answer 6

Repeat the experiment for several potato cylinders, this makes the experiment more repeatable and means anomalous results can be ignored when a mean is calculated.
Be careful of errors e.g. if the potato cylinders weren’t fully dried, the excess water would give a higher mass.