We’d cut three potato chips weighed them, noted this down and then put them in the solutions. We’d make the solutions by mixing distilled water with a salt solution. The solutions we’d use would be in the ratio 100% solution: 0% solution, so it was 1:0, 1:1, 0:1. 1:0 means that for every 1 cubic cm of distilled water we put in we put in 0 cubic cm’s of solution. 1:1 means that for every 1 cubic cm of solution we put in we added 1 cubic cm of distilled water. The solutions and the potato chips would be in boiling tubes in test tubes rack for safe storage. We would leave these for 24 hours. The next day when we would come to check them, after 24 hours, we would take the potato chips out of the boiling tubes to weigh them.
This next part is very important to the accuracy of the experiment. If you were to place the potato chips straight onto the weighing scales then you could have a wide range of anomalous results. When you take the potato chips out of the solutions there is still some of the solution coating the potato chips. This small amount of solution is enough to throw all of your results off by adding weight. Therefore you must dry the potato chips before you weigh them. Also the solution on the potato chips might erode or damage the scales. We placed them on the paper towels and dried them and then weighed them. The weight change was very obvious.
To create a fair test certain aspects of the experiment will have to be kept the same whilst one key variable is changed. I have chosen to vary the concentration of the sugar solution. This will give me a varied set of results from which I hope to make a decent conclusion. If any of the non-variables below are not kept constant it would mean it would not be a fair test. For instance if one of the potato chips was 1cm longer the surface area of the chip would be larger and there would therefore be more space for osmosis to occur. Doing all the tests at one temperature will control the temperature.
For the purpose of my experiment I am going to do all the experiments at room temperature.
To keep the water potential of the potato initially will be kept the same by using the same type of potato, which have been treated in the same way, e.g. have all been cut without being washed and peeled.
The mass of the potato is a dependent variable, and this means that it will be measured
throughout the experiment. I will measure the mass in grams. The potato chip will be
measured before it is put in the solution, and after. This will allow us to see whether
osmosis has taken place, and to what extent.
The volume of the solution that the potato chips are kept in must be fair. The must be totally covered in the solution, and the amount of solution will be kept the same because all the potato chips are the same size.
I am also going to use the same scales to weigh my potato chips. This is because the measurements may slightly vary between scales.
Preliminary Work
We decided to do some preliminary work so that we could see what results to expect in the final experiment. Also we could then get information from them and use that information to compare with our final results these would tell us if we have any anomalous results. In the preliminary work we followed the plan exactly.
On the next page is a graph showing the results.
These results confirmed my hypothesis but theses are only one set so they could be anomalous results. Therefore I had to do more experiments on a larger scale with more variables. The preliminary work did help. It showed me that we had to dry the potato chips before you weighed them. Also when you are inserting the potato chips into the boiling tubes you make sure that you have labeled them correctly, I found out the hard way. All the results pointed in the direction that if there is a higher concentration then there would be a higher decrease in mass and vice-versa.
I think the results were quite accurate as there is no unexplained result and the graph has a smooth curve. The potato chips were nearly the same weight but that problem was overcome by converting them into percentages. The boiling tubes were left in the same conditions overnight in a lab. The temperatures were all the same and there were equal amounts of light on them all.
The Experiment
Next we did the actual experiment this was much like the preliminary work but we used more variables and did them all twice. This was to make the experiment more reliable. We cut the potato’s chips from a potato and weighed them. Then we put them into the different solutions. There were two sets of each solution. There was the 100%, 75%, 50%, 25%, 0% solutions. The next day, after 24 hours, we returned to measure the weight of the potato chips. Once again we dried them on paper towels first. Then placed them in the scales and noted down the results.
This was once again a fair and accurate test. The boiling tubes were kept in a lab; they were all exposed to the same conditions. Therefore whatever happens to one happens to the other.
When we took the potato chips out there was a noticeable difference in the ones that had been in the 0% solution and the 100% solution. The ones that had been in the 0% solution had become rigid and harder. They looked as if they had swollen. This could only mean that they had taken on some of the water and increased in weight. The potato that had been in 100% solution where shriveled and flexible. They had become stringy. There was also a definite decrease in size. This must mean that they had lost water due to Osmosis and the concentration differential. Hopefully my results would prove this.
Results and Analysis
The next few pages are my results. They include graphs and tables. These will show if there are any connections and if my experiment has succeeded.
The results have proved my hypothesis, again. In all three graphs there is a definite slope in the same direction for each graph. The higher the concentration the higher the decrease in mass. There are a few anomalous results but these have been taken into consideration and the line of best fit has been drawn. This proves that there is a connection between concentrations of solutions and the movement of water. In Osmosis water moves through a semi-permeable membrane form a high concentration gradient to a low concentration gradient. Using this fact you can now roughly determine the concentration of a solution. If you look at the table then you can determine which the higher concentration is by looking at the results. If the change in weight is a minus you know that the solution is over 50% concentration. And if it is a plus or zero you know that it is under 50% concentration.
In conclusion I completely agree with my hypothesis and so do the results except for a few anomalous results.
Evaluation
The experiment was very successful in my opinion. I obtained a large quantity of very accurate results from which I was able to create informative graphs. I think I took easily enough results for the amount of concentrations that I was using, and the time that I used for the experiment to last was enough to allow sufficient osmosis to occur. However if I was to repeat the experiment I might well increase the time of the result to allow more Osmosis to happen and possibly find out the saturation point of the chips. The range of concentrations was adequate but I would possibly create more concentrations if I repeated the experiment so that I would have more varied results, i.e. 0.10m, 1.15m, 1.20m, and so on. In my experiment the greatest care was taken to measure the weight of each individual potato chip. The movement of water into and out of the potato chips is accurate but it is a very hard thing to do so a few anomalous results have been made. It is hard because the water molecules are moving into and out of the cells. The cells are very small and are impossible to control or see so we cannot see what is happening. Anything could affect the cells i.e. if they have been damaged or they have been destroyed.
You can make this experiment more accurate by measuring the amount of water left in the boiling tubes as well as the weight of the potatoes. To do this you would have to keep the solutions in a dark, cold area to stop evaporation. Also there is the surface area. If 1000 molecules diffuse through 1cm of cell membrane in 1 minute then it is reasonable to believe that 2000 molecules will diffuse through 2cm of cell membrane .0in 1 minute. Therefore the larger the surface area the more water that can be diffused. So if a potato chip has a large surface area but has the same weight as another potato chip then the potato chip with the larger surface area will take on more water in a set time. For example if a potato chip is cut in a wavy shape or is crinkled it could have the same weight as any other potato chip but it would have a larger surface area. This could affect your results. So you must be careful in cutting the same shape potato chips. The slight difference in our experiment was negligible so we did not take it into account but it might have helped to make one of those anomalous results.
All the anomalous results were negligible. They could be caused by anything. Form a slight increase in room temperature to the cell membrane being damaged when being cut. If I were to repeat this experiment I would try to make sure there are no anomalous results. The experiment would take a longer time and would be conducted in a sterile lab where there are no possible ways of the experiment being effected.
In conclusion the experiment was a success we got the results we expected and they proved our hypothesis. But this experiment could always be repeated maybe on a much larger scale over and over again. This experiment suggests that there is a connection between the concentration of a solution and the movement of water.
