Osmosis Laboratory

PSIBiologyName______

Problem

What determines the direction of osmotic flow?

Materials

Each student needs: apron, gloves, and goggles

Each group needs:

6 clear cups

6 pieces of 15cm Dialysis tubing

12 pieces string 10cm in length

1 plastic medicine cup

10ml Distilled water

10ml 0.2 M Sucrose solution

10ml 0.4 M Sucrose solution

10ml 0.6 M Sucrose solution

10ml 0.8 M Sucrose solution

10ml 1.0 M Sucrose solution

1 Marking pencil

Labeling tape

Calculator

Paper towels

Balance

Enough distilled water to cover dialysis tubes in cups

Time Requirements:

Pre-lab prep (Teacher Time): approx. 60min

Osmosis lab: aprox. 90 min. This time includes data analysis (calculations and graphing), which can be assigned as homework. The actual setup and data collection process should take about 45 min.

Procedure

  1. Obtain six plastic cups and number them from 1 to 6.
  1. Obtain six pieces of soaked dialysis tubing. Open one end of each tube by gently rubbing it in between your fingers. Tie one end of each tube off with a piece of string.
  1. Using a measuring cup, measure out 10ml of each of the six solutions.
  1. Pour the contents of one solution into the first dialysis tube and tie it closed with another piece of string. Continue to do the same thing with the remaining five solutions. Make sure to rinse out the measuring cup in between solutions.
  1. Rinse the outside of each dialysis tube with running water and then use paper towels to dry the outside of each bag.
  1. Record the initial mass of each bag in Table 2.
  1. Place the appropriate dialysis tube into each of the numbered cups and fill each cup with enough distilled water to completely cover each tube.
  1. Begin timing for a total of 30 minutes.
  1. After 30 minutes have passed, remove each dialysis tube from its container and gently blot any excess water from its surface.
  1. Record the final mass of each bag in Table 2 and then calculate the percent change in mass for each tube. % Change = (Final Mass – Initial Mass)/Initial Mass x 100. Record the class averages for % Change in Mass in Table 3.
  1. Construct two graphs. The first graph will be of your group’s % Change in Mass. The second graph will be the class average of the % Change in Mass for each dialysis tube.

Table 2

Solution / Dialysis Bag Initial Mass (g) / Dialysis Bag Final Mass (g) / Change in Mass (g) / % Change in Mass
Water
0.2 M
0.4 M
0.6 M
0.8 M
1.0 M

Table 3Class Data For % Change in Dialysis Bag Mass

Group # / Distilled Water / 0.2 M Sucrose / 0.4 M Sucrose / 0.6 M Sucrose / 0.8 M Sucrose / 1.0 M Sucrose
1
2
3
4
5
6

Analysis

  1. What is osmosis and how does it differ from simple diffusion?
  1. In which of the six setups in this experiment do you think osmosis occurred? Explain.
  1. Explain the relationship of the distilled water in each beaker to the solution inside the dialysis tubes with regards to tonicity (solutes concentration).
  1. What do you think would happen if you placed each dialysis tube in a solution containing 0.4 M Sucrose instead of distilled water?
  1. Why was it important to calculate and plot % Change in Mass as opposed to just using the absolute change in mass of each dialysis tube?
  1. What do you think would happen if you took some of your red blood cells and placed them in distilled water? What would happen to these cells if you placed them in 1.0 M sucrose solution? What would happen if you placed them in blood plasma?
  1. On a hot day, under normal conditions, why is it better to drink water to stay hydrated as opposed to drinking fluids containing salt or other solutes?

Teacher notes:

Pre-Lab Prep:

  1. Cut enough 15cm lengths of dialysis tubing to accommodate all lab groups.
  2. Cut enough10cm lengths of string to accommodate all lab groups.
  3. Prepare 1 L of each of the following solutions:
  4. 0.2 M Sucrose
  5. 0.4 M Sucrose
  6. 0.6 M Sucrose
  7. 0.8 M Sucrose
  8. 1.0 M Sucrose

Note: If using a lab kit, bags of pre-weighed sucrose will be provided with mixing instructions.

  1. Just before the lab, put the cut dialysis tubes into a cup of water.