1: Keep the potato cylinders the same length (2cm). If a cylinder was longer than the other than osmosis will happen quicker because of a larger surface area
2: Use the same potato. There are many different types of potato and each could have different cell structures or may have imperfections in the potato
Background information
Osmosis is the diffusion of water only, through a selectively permeable membrane, from where water is in high concentration (a weak solution) to where water is in low concentration (a strong solution). The experiment I am carrying out is to find the point at which no osmosis takes place where the solution will stop gaining water and start loosing it.
Results
Analysis
From the experiment I have found out that when you increase the molar concentration of the salt solution the potato cylinders loose mass.
My graph of results shows that the potato cylinders gain weight with concentrations of 0m, 0.25m, 0.5m and loose weight with concentrations of 0.75m and 1m. Osmosis goes from a dilute to a concentrated solution so between 0.5 and .075 is where the potato will neither gain nor loose weight. This would probably be at 0.65 molars.
The potato in a solution of lower concentration gained weight because the concentration of the potato is higher than the concentration of the salt solution and when the potato lost mass the concentration of the potato was lower than the concentration of the salt solution. From what we know about osmosis it is where water goes from a high concentration to where water is in low concentration, so when the molar concentration was high the water from the solution went into the potato making it gain weight and vice versa.
So by deductive reasoning the concentration of the potato where osmosis did not take place would be between 0.5 and 0.75 molars. I think that 0.64 is the correct value because it is a round figure half way between the two values and it is difficult to tell the exact value.
My prediction was vague and only in one significant figure. The results support the prediction because the concentration at which no osmosis took place was between 0 and 1 molar. The prediction not incorrect because as I said the prediction was very vague and the preliminary experiment that was carried out was not detailed enough because of time limitations.
Evaluation
The procedure was easy to carry out and was not time consuming to setup. I had one off result at a concentration of 0.5 molars, the potato cylinder gained 2.8% mass but at 0.25m the % change was 1.6% and 0.75m was -1.4%.
This odd result could be explained because of not removing the excess water from the cylinder and therefore because the weighing scales used were very precise to 2 decimal places the water not removed would make a big difference to the weight and the overall result. The error could even be because of error in taking results, although I find that unlikely because the weight was checked twice for each potato to make sure the readings were accurate.
In my experiment I found out that it was hard to take the results as they had to be taken individually all at the same time and therefore some of the cylinders were still going through osmosis. The experiment should have been set up with delays between each canister giving me time to get the results of each cylinder accurately, but unfortunately there was not enough time to do this. But overall I think the reliability of my results based on my method was very good given the equipment that was used in the experiment.
Looking back on the experiment there are a few things that could be changed given more to improve the reliability and the accuracy of the results taken
- Using different types of sugar solution
- Use different concentrations around the 0.65m area for example 0.6 to 0.7 in increments of 0.05 to find out the exact point where osmosis does not take place and prove more accurate results
