Required Practical 03: Osmosis

Question 1

Describe how you would carry out an investigation into osmosis using potato tissue. (8)

Answer 1

1. Prepare a table and cut 3 identical potato cylinders with a cork borer.
2. Trim them to identical lengths with a scalpel (3cm).
3. Measure and record the length and mass of each cylinder, with the right equipment.
4. Measure and pour 10cm³ of the 1M sugar solution, 0.5M sugar solution and distilled water into separate labelled boiling tubes.
5. Add a potato cylinder (of known mass and length) to each tube and leave them overnight in a test tube rack.
6. Remove cylinders from tubes and blot them with paper towels.
7. Measure and record new information of each cylinder (length and mass) in the table
8. Calculate the percentage change for each cylinder and plot a graph using this information; Repeat the experiment (IP) to get a mean value.

Question 2

Why is it necessary to use a cork borer to cut the cylinders?

Answer 2

Results in equal sized samples (diameter) so changes in length and mass can be compared easily.

Question 3

Why is it necessary to blot the cylinders with paper after removing them?

Answer 3

Blotting cylinders allows masses to be comparable - each cylinder may have a different amount of water on its surface, so masses may vary.

Question 4

What safety precautions should be taken with this experiment? (2)

Answer 4

• Handle cork borer and scalpel with care.
• Handle boiling test tubes with care.

Question 5

What would be in the x-axis of your table?

Answer 5

The solutions

Question 6

What would be in the y-axiz of your table? (2)

Answer 6

• Initial, Final, Change in lengths (mm).
• Initial, Final, Change in mass (g).