Concentration of sugar solution: the higher the concentration of the sugar solution, the more water will be able to move across the membrane and therefore the mass of the potato will decrease because no sugar can pass through the membrane as the molecules are too big.
Mass of potato: the higher the mass of the potato, the longer it will take for osmosis to take place because there are more molecules to pass across the semi-permeable membrane.
Amount of sugar solution: the more sugar solution that there is, the quicker it will take for osmosis to take place because there would be less water molecules to travel across the membrane and therefore it will take less time for them to move across the membrane.
Type of potato: different potatoes may absorb at different rates. Some may absorb more quickly and others less quickly.
Time potato is left in solution: more or less solution may be absorbed depending on time. More solution may be dissolved if the potato is left in solution for a longer period of time.
Surface area of potato: the amount of surface area exposed to the solution, may affect the rate of osmosis. It may be that the smaller the surface area of the chip, the quicker the rate of osmosis as there are less molecules to travel across the membrane.
Light intensity: the amount of light may affect the rate of osmosis, due to the heat the light may generate. Therefore the more light the solution is exposed to the quicker the rate of osmosis, because the warmer the solution would be, therefore increasing the kinetic energy between the molecules and speeding up the rate of osmosis.
Variable
The variable I have chosen to control is the concentration of the sugar solution. I will change the concentration of the sugar solution from 0% sugar to 50% sugar. With 10% intervals in between. Therefore I will experiment this variable at 0%, 10%, 20%, 30%, 40% and 50%.
Prediction
I predict that the higher the concentration of the sugar solution, the more water will travel across the semi-permeable membrane. Osmosis is the movement of particles of one solvent of a solution, in this case water, across a membrane and therefore other constituents cannot pass through the membrane, in this case the sugar. To see if the rate of osmosis has been affected, after I collect all my results, I will calculate the percentage mass average. I will do this by subtracting the original mass from the final mass, dividing the answer by the original mass and multiplying the answer by 100.
final mass-original mass
x100
Original mass
To ensure a fair test, I will keep all the factors mentioned above, the same. I will use a potato cylinder which is 50g and I will use only one size potato borer to ensure that the potato cylinder is always of the same surface area. I will conduct the experiment in the same place every time so not to change the light intensity and I will try to finish the experiment in one lesson so that I do not need to spread the experimental period over two weeks just in case the conditions change. I will use the same type of potato throughout the experiment and I will keep the potato in the solution for only 10 minutes every single time. I will keep the amount of solution at 10cm3 throughout the whole experiment and I will keep the temperature of the solution at room temperature (I will not heat it or cool it).
To ensure safety, I will wear an overall and goggles to protect my body and my eyes from any splashes or spillages that may occur around the lab. I will take care when walking around with test tubes or scalpels so that I do not bump into anyone or cause any accidents. The potato cylinders will be cut using a potato borer on a white tile so that I do not cut myself or the table.
Apparatus
- Test tube
- Potato
- Scalpel/knife
- Tile
- Potato borer
- Stopwatch
Method
- I will set up the apparatus as shown on the diagram
- I will pour the concentration of sugar solution being tested into a test tube.
- I will cut a potato cylinder using a potato borer, weigh it using scales and measure its length and thickness and make sure that all the potato cylinders are the same measurements to ensure a fair test.
- I will record the weight of the potato cylinder and place it in the test tube with sugar solution.
- I will start the stopwatch.
- Once 10 minutes have passed I will take out the potato cylinder and weigh it and record the weight.
- Then I will repeat steps 2-6 again but with a different concentration of sugar solution.
- Once I have collected all the results, I will analyse them and decide if my prediction was right. I will do this by analysing results and graphs.
Diagram
