Experiment equipment
Chemicals:
Distilled water
0.0mol dm-3 sucrose solution – distilled water
0.5mol dm-3 sucrose solution
1.0mol dm-3 sucrose solution
2.0mol dm-3 sucrose solution
Apparatus:
Boiling test tubes x 4
Test tube rack x 1
Visking tubes x 4
Syringe
Clock
Paper towels
Measuring scale
Methodology
The test tubes were prepared first. This was done by labelling each one with 0.0mol dm-3 sucrose solution, 0.5mol dm-3, and so forth with all four concentrations. This is so that the test tubes correspond to the correct Visking tubing. Each were then filled to three quarters with distilled water, and placed in a test tube rack in the order of least concentration to most.
The visking tubes were then filled with the sucrose solutions. To carry this out, each tube were wet under a tap, so that they open. One end was tied with a knot, to close it up from losing any solution. They were each then filled. The first was half filled with distilled water, being the 0.0mol dm-3 concentration of sucrose solution. The next three were filled with each of the other concentrations by syringe. To keep the experiment consistent they were all half filled. They were tied with another knot on the opposite end, keeping a small amount of space within the tube for the flow of water.
The outside of the visking tubes were washed under a running tap and dried with paper towels, the knots were also squeezed to take out any water absorbed. Each was then weighed using the digital weighing scale and this mass was recorded in the results table. Once all four were measured, they were simultaneously placed into the test tubes on the rack, and the timing had begun.
At every 10 minute intervals the visking tubes were taken out of the test tubes, placed on paper towels and dried, again squeezing out any solution in knots. These were weighed and noted in the table and then placed back into the test tubes. This was repeated for 40 minutes.
Results
Table 1: Weight change of visking tubes with different concentrations at 10min intervals
Table 2: Percentage change in mass of visking tubes with different concentrations.
The above information was calculated using the following method.
Percentage change in mass = mass – initial mass x 100
Initial mass
Table 2 is shown in graph 1 on the following page.
Conclusion
This experiment was carried out to find the effect that different concentrations of sucrose solution have on osmosis using Visking tubes. The graph shows that there was a very low rate of diffusion within the visking tube containing 0.0mol dm-3 sucrose solution, and therefore the rate of diffusion gradually increases with increasing concentrations of sucrose solution. These results accept the prediction made.
Diffusion should not occur when a visking tube containing distilled water is placed within a test tube containing distilled water, as the concentrations are equal. The tube containing 0.0mol dm-3 sucrose solution is distilled water, though in the graph a percentage change of 0.974% is shown. This could be due to human error of weighing the visking tube. As mentioned the knots absorbed some solution, if they were not dried, the weight would be more.
