Aim:
My aim is to investigate the effect of varying concentrations of a certain sugar solution on the amount of osmotic activity between the solution and a potato chip of a given mass.
Variables:
Variables are the things that we are going to change during the investigation, and are things which will affect the experiment on the whole. One of the variables will be the concentration of sugar in the solution. This will have a big impact on the experiment as different concentrations of sucrose will affect the potato chips in different ways. For the purpose of my experiment I am going to do all the experiments at room temperature.
Another variable will be the type of membrane used in the investigation. This is because different membranes have different properties, such as different sized holes. A change in membrane can cause the process of osmosis to lengthen or to not function properly.
An additional variable which could affect the experiment is the type or age of the potato. This could affect the investigation because an older potato could react differently to osmosis, or have some sort of ‘side effect’. I will treat each potato chip carefully so as to keep the test fair. For example, I will cut all the potatoes with the same knife and without being washed, as well as not peeling potato.
The mass of the potato will be a dependant variable, meaning that it will be measured throughout the experiment. All measurements of the potatoes will be taken in grams, and the chip will be measured before and after entering the sucrose solution, so as to observe whether osmosis has taken place, and if so, to what extent.
Some things during the experiment will not be changed, as this will not allow a fair test to take place. These things are the volume of sucrose solution. This is because all chips will be of roughly the same length and of all the same mass. This means that each chip should be covered with the same amount of sucrose solution to allow osmosis to take place.
Also, I am going to keep the balances I use to weigh the chips the same, because different balances can have slightly different measurements.
Preliminary Experiment:
We conducted a preliminary experiment in the biology class to help us with our investigation of osmosis. We used concentrations of 0% (plain water) and 20% sucrose. The main variables that could have affected the experiment were the concentration of sugar solution, the type of membrane and the temperature. The results were as follows:
As you can see from the table, there was a definite pattern in the reactions of each potato chip. In the solution with no sucrose in, the chip increased in length and mass, due to osmosis. With the solution of concentration 20%, the chip decreased in both mass and length.
Prediction:
From the preliminary experiment, I can predict that during this investigation, the potato chips will decrease in mass as the concentration of sugar solution increases. This therefore means that the chip will increase in size when there is no concentration of sugar present in the solution (ie, distilled water). I reached this hypothesis as a result of my pilot experiment, because of the size of the molecules. The concentration of water molecules inside the potato chip cells will be higher than that in the surrounding solution, as it is a solid and the solution is a liquid. The most movement of water molecules will be form the potato chip into the solution. This is because they are going from an area of high concentration to an area of low concentration. The weight (mass) of the potato chip will decrease because of the vacuoles.
Planned Method:
A range of sucrose sugar solutions will be prepared with concentrations 0%, 1%, 2%, 5%, 10% and 20%. This will be done by adding varying amounts of distilled water to varying amounts of sucrose solution. Sections of potato will be cut using a standard kitchen knife and will be weighed using a pair of scales. This part of the preparation must be done very accurately as a change in the surface area may allow more or less osmosis to occur.
Three chips will be placed in each test tube each time so that I can take an average for each tube. I will use 30 ml of each concentration of sugar solution and once in the test tubes they each will be labeled. The potato pieces will then be placed in the different test tubes and then left overnight. Then the potato pieces will be removed, the surface solution removed using paper towels and then they will be re-weighed. If I then have time afterwards I will repeat this experiment again as to obtain a second set of results. This will hopefully produce more accurate results from which I will be able to draw a more accurate conclusion.
Method:
Firstly, I took a healthy, well sized potato, and checked that it was both healthy and hard. Then, using a standard kitchen knife, I cut the potato into a 7cm by 5cm by 4cm cuboid shape on the white tile I was using. Then, using the knife and the weighing scales, I cut 18 chips, each with a weight of between 2 grams and 2.05 grams. I could not get the mass to an exact number as I was not using special cutting materials. However, during the cutting of the potato, due to the unreliable material which I was presented with, some of the chips were slightly lighter than the rest of the chips in regards to mass. Therefore I had no other option but to take another potato and cut out the rest of the chips. This meant that the experiment was no longer a fair test. Nevertheless, I continued with my investigation.
I then filled the test tubes with the sucrose solution. The solution was already pre-mixed, so I measured out 30 ml of each concentration of sugar using a measuring cylinder and filled each of the beakers (6 in all). I then put three chips in each test tube. I did this in order to be able to work out an average, and also to be able to plot a more accurate graph. My experiment was then put into a fridge by my teacher. This caused the reactions between the potato and the sugar to slow down. I then left it overnight…..
The next day I returned, found my investigation and got back to work. In preparation, I laid out some paper towels and drew up a simple table for my results. Then, I got my test tubes with the solutions and potato still inside, emptied them out and dried the chips on the paper towels. I desiccated each chip, and weighed them individually. Each potato was measured accurately to one decimal place and the results were recorded.
Precautions:
As was stated in the planning section of my coursework, I had to keep all of the different non-variables the same, to make sure that none of them affected the results of the experiment in any way. Also, whilst cutting the potato chips, I had to very careful as the knives were relatively sharp and could easily cause a serious injury.
Another precaution I took was to measure out the solutions carefully and very accurately so as not to ruin the results in any way. And finally, I had to ensure that every time I handled the potatoes my hands were clean and dry. This was to stop any kind of contamination and to make sure that I did not pass on any extra water onto the potato in any shape or form.
Results:
As you can see from the table of results, there was no real pattern in the average or in the change. In my view, this was owing to the fact that we used chips from different potatoes and that our potato chips were put into the fridge overnight, thus slowing down the process of osmosis. The table shows that in general, osmosis took place in all concentrations with the exception of 20%. However, as there is no real pattern to the averages or to the change, we cannot say for sure that Osmosis affected the potato chips. The poor results were due to two things. Firstly, the potato chips were cut from different potatoes due to human error. These caused the most change as the two potatoes could not have been identical and had different physical and biological properties. The other thing that affected the results were that the samples were put into the fridge overnight, slowing down the process of osmosis drastically.
My prediction was proved to be wrong apart from in the 20% solution. This was down to the pilot experiment being conducted differently to the real experiment. Had this been done properly, my prediction would have matched the results.
My method showed how the experiment should be done, and I have full confidence that should I repeat the test; my method will make the results come out better.
The only result that didn’t seem to fit in with the pattern was the chip in 20% sucrose solution. I have already explained the reasons, and in future tests I will make sure not to make those mistakes again.
Overall, the experiment wasn’t what I expected, however, I learned a lot of things regarding osmosis and diffusion, and I have better ideas of how to conduct the experiment in the future should I wish to repeat it.