For example:
Some water is placed in a science beaker (A), and then some 20% sucrose 80% water solution is placed in a piece of visking tubing (D).
When this is placed in the water contained in the beaker (A) there becomes an imbalance of concentrations either side of the semi-permeable membrane, on the inside of the membrane there is a stronger concentration or ratio of sucrose against water than there is in the outside.
Therefore the sucrose would be required to equalise, by 10% or so moving to the outside of the tubing, there comes the problem.
Due to the size of the small holes in the visking tubing, big molecules, such as sugar, C6H12O6 that is 24 atoms big, cannot pass through, however small ones such as water, H2O with three atoms to a molecule, can.
Therefore, since there is no way of moving the sugar, the best thing to do is to add more water to the inside of the visking tubing. By osmosis and diffusion, the smaller molecules move into the visking tubing whilst the bigger sugar molecules stay.
That is osmosis. Plants also use this method to provide nutrients and various chemicals to their cells.
Equipment:
For my experiment I will need a total of:
Four test tubes; one potato; 2%, 5%, 10%, 20% sucrose and water solution; one knife; one marble cutting plate; aluminium foil; four sticky labels.
Method:
- Cut the potato into equal strips and weigh them. Record the weight.
- Fill each test tube with 100ml of the different solutions, so that you have one 100ml – 2% solution tube, one 100ml - 5% solution tube, etc…
- Leave all the potato chips in for 15 minutes and record the new weights.
- Repeat the experiment for reliability.
Things I will keep the same are:
- The amount of solution in each test tube.
- The rough size of the potato chips.
- The time taken for each experiment.
Things I will change are:
- The strength of the solutions.
To ensure fairness I am going to perform the test twice and make averages during the graphical stages.
Diagram:
Results:
Result Set One:
Result Set Two:
Results Average:
Graphs:
Here are several graphs of the results, and the averages of the results:
Results Table One:
Results Table Two:
Results Table Average:
Analysis:From these graphs and the result tables I can see that my prediction was correct in most cases.
The potato contained a little starch, so when it was placed in plain water, a little water was absorbed into the potato making it swell a little, however when the sucrose solution was placed on the outside water was sucked out of the potato. It seems, there was a connection between the strength of the sucrose solution on the outside and the amount of water sucked out.
It appeared to steadily increase.
The process of osmosis causes water to travel from a lot concentration (generally the potato), to a higher concentration, the outside of the potato.
Therefore, the potato got more flaccid in a greater concentration.
Evaluation:
I feel the experiment went well, it proved a scientific concept and helped me learn more about a subject that I was weak on.
I did encounter one or two odd results, such as the 5% sucrose solution in results table two and results table of the averages, however I feel this must have been due to human error, possible reasons for this may have been, weighing incorrectly, or the usage of the wrong strength of sucrose solution, however, this does not harm the overall results much.
To prevent this happening again, I would have to conduct the experiments many more times and collect the averages.
The next step in this would be to perform the test on other materials, such as visking tubing, and then to take averages and compare the results, even find out which is more permeable.
