Osmosis

• Cut tubes of potato using a cork borer
• Trim the potato cylinder so it is at a controlled length
• Record the mass of the potato cylinder
• Put the cylinder in a boiling tube of solution and leave for a fixed period of time
• Remove the cylinder and blot dry
• Record the mass of the potato cylinder
• Measure and record the new length
• Repeat two more times to identify outliers and calculate an average
• Repeat for different concentrations
• Calculate percentage change in mass
• Use a balance to measure mass
• Osmosis is the movement of water through a partially permeable membrane from an area of high water concentration to a lower concentration of water
• Dry the potato piece before weighing it again so that excess water does not contribute to the mass
• Potential sources of error when investigating osmosis

  • concentration of solutions, evaporation from tubes, accuracy of balance
• A potato piece left in solution would increase in mass as the solution would be more dilute than the potato piece and so water has entered the potato by osmosis
• A potato piece left in solution would decrease in mass as the solution would be more concentrated than the potato piece and so water has left the potato by osmosis
• A potato piece left in solution would not change in mass when the concentration of the solution is the same as the concentration of the potato
• Control variables when determining the concentration of a potato piece would be time in solution and volume of solution