Plan
I am going to investigate the affect of solutions of different concentrations on the weight of potatoes.
Apparatus
The apparatus that will be needed for this experiment are:
- 2 test tubes
- 1 top pan balance
- 1 test tube holder
- 2 pieces of potato
- Strong sugar solution
Method
- I will pour 5 cm³ of different salt concentrations (0, 0.2, 0.4, 0.6, 0.8, and 1 Molar) into separate test tubes.
- I will then cut 6 potato pieces that are 2cm in length and weigh them.
- I will place one potato piece in each of the test tubes and leave them to stand for 20 minutes.
- I will remove the potato pieces from the test tubes and dry them to get rid of any water on the surface of them.
- I will then weigh the potatoes on a top pan balance and measure them.
- I will then repeat the experiment to ensure the results are reliable and I will then find an average.
Fair test
To ensure that these experiments are a fair test I will keep the following factors constant:
- The length of the potato pieces- all potato pieces will be 2cm long.
- The surface area of the potato pieces- the potato cylinders that the pieces are cut from will all be the same shape.
- The freshness of the potato (as fresh as possible)- potatoes as similar as possible will be used in the experiments.
- The top pan balance- the same top pan balance will be used to weigh every potato piece before and after the experiment.
- The temperature- all the tests will be carried out on the same day.
- The amount of the solution in the test tube- there will be 5cm³ of salt solution in each test tube.
Safety
To ensure the experiments are safe a will handle the test tubes carefully and clean up any glass quickly in the case of any breakages.
Results
1st Experiment
2nd Experiment
Average
I also recorded the results for the lengths of the potatoes before and after placing them in the salt solutions but all of the potato pieces decreased from 2cm to 1.9cm whatever concentration they were placed in.
Conclusion
The results show that as the concentration of the salt solution increases then the percentage change in mass of the potatoes decreases. This supports my original hypothesis that the stronger the solution is that the potatoes are placed in then the less the potatoes will weigh. This occurs because the water in the potatoes diffuses into an area of lower water concentration. When the concentration of the salt solution is higher then the water concentration of the solution is lower so more water moves from the potatoes into the solution.
However, the results start to level off between 0.6 Molar and 1.0 Molar so the hypothesis is not supported as strongly as if the percentage change in mass had continued to decrease.
Evaluation
The results should be accurate because the potatoes were weighed to the nearest centigram using a top pan balance. The results should also be valid as most of the variables that could affect the results were controlled. However, the temperature may have changed while the experiments were being carried out and the freshness of the potatoes could have varied. The reliability of the results for most of the concentrations is good with the biggest difference between the two sets of results being 5.02%. However, this excludes the 1.0 Molar concentration that has a difference of 7.79% and this means that its reliability is questionable. Also the result is not situated near the line of best fit on the line graph so this suggests that it is an anomalous result. This is mainly due to the result from the first experiment and this result could have been affected by the potato not being properly dries before it was weighed at the start of the experiment.
The experiment could be developed by investigating a larger range of concentrations of the change in mass of the potato or investigating a greater number of concentrations within the same range i.e. 0.1M, 0.2M, 0.3M…1.0M. The experiment could also be extended by investigating the effect of temperature, the amount of the solution or the surface area of the potatoes on the percentage change in mass.
