Prediction: I predict, that as the concentration increases, the mass and length if the potato chip will decrease. I think this will happen because, the higher the concentration of sucrose in a solution the lower amount of water. When the potato chip is put into the solution, it will by osmosis lose some of its water.
However if the potato chip is placed in a solution of 0 molar concentration (which is pure water.) it should gain mass, width and length. This is because the solution has more water potential (it’s molecules ability to move) than the potato chip, and so water moves from a region of high concentration (the solution) to a region of low concentration (the potato chip.)
Apparatus:
Measuring cylinder (to measure the volume of sucrose solution)
Scalpel (for cutting the potato chips into size)
Cork borer (to cut the potatoes into cylinders)
White tile (to cut the potato on using the scalpel)
Test tube (to store the solution and the potato in)
Test tube rack (to store the test tubes in)
Potato (to put in with the solution in the test tubes0
Beaker (to store the water until it is needed)
1 molar – sucrose (to vary and put in the test tubes)
Method:
- cut 16 tubes of potato out of the same potato(being careful not to cross them)
- By using a measuring cylinder place a total of 10 cm made up of sucrose solution and water. (As shown how to in table on the left.) Repeat each concentration 3 times then take an average.
3. Cut the ends of the pieces (as there is an impermeable skin layer, which if not removed could prevent osmosis and therefore make the experiment and unfair test) and cut them to the correct length.
- Weigh each and record the mass in a results table. .
- Mark each of the test tubes so you know which test tube holds what concentration of solution.
- Make the sucrose solutions by adding varying amounts of sucrose to varying amounts of distilled water.
- Place 1 piece of potato in each test tube.. Make sure you know where each piece of potato has been placed so you can identify its original weight after the experiment.
- Leave the potatoes in the solution for 40 minutes.
- After the 40 minutes drain the solution form each test tube, weigh the potato nand record the mass in the results table
- Draw a graph.
Fair Test
For the results to be accurate and reliable, the experiment must be a fair test. A fair test is when all the non-variables in the experiment are kept the same. This means the factors like surface-area and volume of solution are all kept the same. For it to be a fair test, the following should and will be accounted for:
- The pieces of potato must be the same width length, because they must have the same surface area exposed to the solutions. This means that if one cylinder is exposed to more solution than another cylinder, then the one with the larger surface-area has a larger contact with the solution. To do this they must be measured down to a mm and the same cork borer must be used throughout the experiment.
- The weights must also be as accurate as possible and therefore the scales must be extremely sensitive. When the balance is being used, before each potato cylinder is placed on the scales the scales must be set 0.
- All the pieces must come from the same potato. If I used a different potato, the second potato may have a higher or lower solute concentration.
- All the pieces must remain in the solution for the same amount of time. If one pieces of potato stayed in the solution longer than a different one then it would have had more time for osmosis to occur. This could lead to inaccuracies in the results.
- I will have to keep the potatoes and solutions at the same temperature (room temperature in this case)throughout the experiment.
Analysis of research.
The graph gives the line of percentage change in length of the potato chips. The graph is a curve that slopes downwards. Because the line is not straight and passes through the origin at 0.48 Mol. There is a pattern on my graph, and this is, as the concentration of the solution increases, the percentage change in mass decreases. The graph shows that the percentage gain and loss in inversely proportional to the concentration. The gradient changes in my graph. It gets steeper as X-axis gets bigger. This is because the potato chip is becoming as flaccid as it possibly can, and so the change in mass of each molar concentration is becoming closer and closer together. This shows that my results are fairly reliable. My graph fits in with my prediction of the experiment graph.
It shows that the potato cells increase in mass in solutions with a high water concentration and decrease in mass in solutions with a low water concentration. This graph of the change in mass helps prove the point of complete plasmolysis, whereby the potato cannot expand and take in any more water. As you can see as the molar concentration increases the change in mass decreases.
Evaluation
The experiment was very successful in my opinion. I obtained a large quantity of accurate. I think I took easily enough results for the amount of concentrations that I was using, and the time that I used for the experiment to last was enough to allow sufficient osmosis to occur. However if I was to repeat the experiment I might well increase the time of the result to allow more osmosis to happen and possibly find out the saturation point of the potato chips. The range of concentrations was adequate but I would possibly create more concentrations if I repeated the experiment so that I would have more varied results, i.e. every 0.1m in between 0.4m and 0.5m , and so on. This way would have allowed me to also find out the isotonic point far more accurately as the one that I estimated is very approximate.
