Size of potato: The size of the potato in each experiment should be kept the same because if there is a larger surface area, there is more space for the solutions to move through, making the experiment inaccurate if some pieces of potato are larger than others.
Stirring: We will not stir any of the solutions because this may speed up the osmosis.
Temperature: The temperature should be kept similar because heat speeds up the movement of the water particles, speeding up the osmosis. We should measure the temperature using a thermometer.
Type of potato: The type of potato should be kept the same because different types of potato may have different molarities of solution in their cells.
Key Factor: Molarity of solution: The key factor in this experiment is the molarity of the solution. This will be varied to find out the molarity of the solution inside the potato cell.
Pilot test findings: We carried out a pilot test using solutions of 1 molar, ½ molar, ¼ molar and 0 molar (pure water). We found that the difference in weight of the potato in the solution of 0 molar went up by 0.1g, and the weight of the potato in the solution of ¼ molar went down by 0.3g. This shows us that the molarity of the solution inside the potato cell is somewhere in between these two molarities of solution, so we will use solutions between 0 molar and ¼ molar in the main experiment.
Method: Make up 100ml of each of 5 solutions; 0.4 molar, 0.3 molar, 0.2 molar, 0.1 molar and 0 molar.
To make 0.4 molar salt solution, mix 40ml of 1 molar salt solution with 60ml of pure water.
To make 0.3 molar salt solution, mix 30ml of 1 molar salt solution with 70ml of pure water.
To make 0.2 molar salt solution, mix 20ml of 1 molar salt solution with 80ml of pure water.
To make 0.1 molar salt solution, mix 10ml of 1 molar salt solution with 90ml of pure water.
To make 0 molar salt solution, use 100ml of pure water.
Cut five equal pieces of potato and record the weight of each one. Put one piece in each solution and leave in the solutions for 5 minutes. Then take them out of the water and re-weigh them, recording the weight.
Safety: We will keep the experiment safe by being careful when cutting the potatoes and keeping the work area tidy.
Fairness: We will keep the test fair by trying to keep all the factors except the variable the same.
Prediction: I predict that the mass of the potato in pure water will increase because the water moves into the cell to try and balance the solutions inside and outside the cell. When the solution we are using is the same as the solution inside the potato cell, the mass will stay the same because the solution does not need to be balanced out so the amount of water moving into the potato cell is the same as the amount of water moving out. The molarity of the solution inside the potato cell will be between 0 molar and ¼ molar.
Conclusion
As the concentration of the solution increased, the average percentage difference between the start weight and the end weight decreased. This tells us that where the weight stays the same, this is the molarity of the solution inside the cell. From the graph, we can see that this point is around 0.85 molars.
At 0 molars, the weight increases by
