The temperature affects the rate of osmosis because it changes the kinetic energy that the particles have, by increasing it, so the particles move faster and have a higher chance of passing through the semi- permeable membrane.
The Purpose
The purpose of this investigation is to find out where the iso- osmotic point is for a 1 cm size of potato for different concentrations.
The iso- osmotic point is where the concentrations in the cells, and the concentrations of the solutions are the same. When this happens, osmosis has not stopped it still continues to take place, but it keeps the concentrations of the two different solutions the same.
Preliminary Work
Method:
- 3 potato chips were cut to 3 cm long, then were each weighed, and their mass recorded.
- One was placed in distilled water, and the others in 0.5 and 1.0 molar sucrose solutions. They were then left for about an hour.
- After an hour the chips were removed, blotted, and re-weighed and re-measured.
- The change in mass and length was recorded, and the % change was calculated. The results are shown below.
The Constants:
- The dimensions of the chip
- The amount of solution
- The concentration of the solution
- The room temperature
- The time in the solution
In this investigation we are measuring the mass and the length of the chip, before and after it was put in the different solutions.
Here is a graph of the Preliminary results:
Prediction:
The prediction that we have made for this experiment is that when the concentration of the sugar solution increases, the mass and the length of the chip will decrease. This is because when there is more sugar in one of the solutions, then osmosis will take place, and will level out the concentrations of the two solutions. This can be proved from the results of the preliminary experiment, as when the solution was 1.0 mol/dm³, the percentage mass change was –11.0, and the percentage length change was -5.2. This is a high percentage change as shown by the results of the distilled water: The percentage mass change was 10.0, and the percentage length change was 3.2.
Actual method:
- 7 different solutions of sucrose were measured from distilled water to 1 mol/dm³
- Bore a potato, to get 3 1 cm chunks
- The bored potato will not be 1 cm, so cut it on a measuring tile to 1 cm using a razor
- Skewer the 1 cm potato chunks onto a pin with a small gap in between
- Weigh the pin with the chunks on and record
- Put the skewed chunks into the different solutions, noting down which test tube had which solution in
- Leave the test tubes in a cold place for 3 days
- Take the test tubes out and note down the length of each individual chunk
- Dab off any excess solution and weigh the pin with all of the chunks on
- Note all results into a table
Safety
- Be careful with the glass test tubes
- Be careful with the razor
Results
Conclusion
The results show that our prediction was right, I that when the concentration of the sugar solution increased, the mass and length decrease. This is because of osmosis. There are more water particles in the chip than the sugar solution, so the water molecules pass through the membrane and level out the concentration of the solution. When there is a higher sugar concentration, more water has to be taken from the chip so the mass and length decrease, as 75% of the chip is water. Once the concentrations are balanced, osmosis does not stop, but carries on keeping the levels the same. This can be done because it is not active, and does not use energy to pass the molecules through the membrane.
Evaluation
To improve the accuracy of this experiment, we could have;
- Weighed all of the pieces of chip separately.
- We could have timed the length of the chips being in the fridge, and kept it constant, and not roughly 3 days after