Investigating how concentration of salt solution affects osmosis in potato

“Investigating how concentration of salt solution affects osmosis in potato”

By Neil Grant

1117

Planning

We have been asked to investigate the effect of osmosis on potato chips. Osmosis is the diffusion of water from a lower concentration of solute to a higher concentration of solute, through a membrane.
I have chosen to investigate the effect of the water potential/concentration of solution on potato chips. This means that I will put potato chips into salt solutions of different concentrations. These concentrations would be ones such as these; 0.25mola, 0.5m, 0.75m, 1.0m and distilled water.
There are other factors (variables) involved and these are;
¨ Temperature
¨ Water potential of potato initially
¨ SIZE of potato
¨ Light intensity
¨ Mass of potato dependent variable
¨ Volume of solution potato chip is in
¨ Type of potato
¨ Time left in solution
¨ Surface area of potato chip
¨ Use the same balance to measure chip

If I am going to conduct a fair test, then I am going to have to control these other factors. 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 size of the potato is very important. This is because if the size of the potato varies,
so will the amount of mass is looses or gains. I will cut all the pieces of potatoes, to the
same size. We will be given potato chips with the same width and dimensions, but the
length of them will differ, (due to potatoes being of uneven shapes). The potato chip will
be 3cm in length.
The light intensity will be kept the same by doing all the experiments in the same room,
with the same light intensity, (no extra light will be shone on the experiments, nor will
there be any experiments kept in the dark).
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. The amount of solution I cover each chip in will be
80ml.
The type of potatoes we use are going to be kept the same, because different potatoes
may absorb at different rates. For this experiment I am going to use the same type.
The time the potato chip is left in the solution must be kept the same in each
experiment. This is because more or less solution may be absorbed depending on time. I
am going to keep each potato chip in each solution for 10 minutes, in a beaker.
The surface area of the potato chips will be kept the same by having all the chips the
same size. This must be kept the same because the amount of surface area exposed to
the solution may affect the rate of osmosis. The thickness of the chip will already be the
same, so we will cut the length so that each chip is 5cm long.
To make the mass readings more fair, we will take each chip of the solution, roll all the surfaces gently on a paper towel, (2 seconds on each surface), to remove all excess solution, and we must not squeeze the chip.
We are also going to use the same balance to weigh my potato chips. This is because the measurements may slightly vary between scales.
I predict that the higher the concentration of salt solution the more water will move out of the potato chip. We know that osmosis the flow of one solvent, (water) of a solution through a membrane while the other constituents are blocked and unable to pass through the membrane (semi-permeable). Experimentation is necessary to determine which membranes permit selective flow, or osmosis, because not all membranes act in this way. Many membranes allow all or none of the constituents of a solution to pass through; only a few allow a selective flow. As the potato is a plant cell, it contains a vacuole and a cytoplasm. The cell membrane is also partially permeable i.e. it lets some substances in but not all substances. This means that water particles can diffuse into cells by osmosis if the cells are surrounded by a weak solution. (Osmosis is the movement of water molecules from a high area of water potential to an area of low water potential through a selectively permeable membrane.) If the cells are surrounded by a stronger solution, e.g. salt water, the cells may loose water by osmosis.

To ensure safety, The potato chips will be cut on a white tile with a scalpel so that no one will be cut. Also while using scalpels everyone will have to wear safety goggles.
My experiment is not experimenting the how permeable the membranes are, but it is testing the rate of osmosis with different solutions. We also know that diffusion of water will occur from a lower concentration of solute to a higher concentration of solute. I am saying that the higher the concentration that the potato chip is exposed to, the more water will move out of it making it lighter. Here are some diagrams to help explain.

Obtaining Evidence

This is a preview of the whole essay

Obtaining Evidence

My graph is a curve that slopes downwards and does not go through the origin. Because the line is not straight and does not pass through the origin, it means that the percentage gain/loss in mass and morality are not directly proportional. However, there is a pattern on my graph, and this is, as the morality of the salt solution increases, the percentage change in mass decreases. The gradient does change in my graph. it gets less steep as 'x' gets bigger. This is because the potato chip is becoming as flaccid as it possibly can, and so the change in mass of each morality are becoming closer and closer together. All of my results lie close to my best-fit curve. This shows that my results are fairly reliable. My graph fits in with my prediction of the experiment graph.
The percentage gain/loss in mass and morality are not directly proportional
are not directly proportional to each other, so I decided to test another simple way of seeing whether the results are related. This is to see if they are indirectly proportional. This is where you get the results and, x, and put 1 over them, 1/x. The graph is not a straight line through the origin which shows that the percentage gain/loss in mass and morality are not directly proportional either.
The average distilled water gains in mass. This means that osmosis takes place and that the water moves from the beaker into the potato. The matches my initial predictions, and fits in with my prediction graph as well. The point where the line crosses the x-axis is the isotonic point. This is where no osmosis is taking place, i.e. no water is moving in or out of the potato. The next point, 0.25 mola looses approximately 4.0g. This shows that the water potential of the salt solution in the beaker is weaker than that of the potato chip. The next, 0.50 m, looses approximately 8.0g in mass. This shows that the salt solution has an even weaker water potential than 0.25 m and that osmosis took place. This is why the potato lost even more mass, and it shows that the water potential in the beaker is less than that of the potato chip. Also that the potato is trying to make the water potential of the fluid on both sides of the semi permeable membrane the same, (osmosis from the potato to the salt solution, from a higher water potential to a lower one). This pattern carries on through the graph, and even more mass is loss, as more water moves out of the potato. My results tally with my initial predictions. These were that osmosis would take place, and as the water potential decreases, morality increases, the percentage change in mass will decrease.

Analysis

My graph is a curve that slopes downwards and does not go through the origin. Because the line is not straight and does not pass through the origin, it means that the percentage gain/loss in mass and morality are not directly proportional. However, there is a pattern on my graph, and this is, as the morality of the salt solution increases, the percentage change in mass decreases. The gradient does change in my graph. it gets less steep as 'x' gets bigger. This is because the potato chip is becoming as flaccid as it possibly can, and so the change in mass of each morality are becoming closer and closer together. All of my results lie close to my best-fit curve. This shows that my results are fairly reliable. My graph fits in with my prediction of the experiment graph.
The percentage gain/loss in mass and morality are not directly proportional
are not directly proportional to each other, so I decided to test another simple way of seeing whether the results are related. This is to see if they are indirectly proportional. This is where you get the results and, x, and put 1 over them, 1/x. The graph is not a straight line through the origin which shows that the percentage gain/loss in mass and morality are not directly proportional either.
The average distilled water gains in mass. This means that osmosis takes place and that the water moves from the beaker into the potato. The matches my initial predictions, and fits in with my prediction graph as well. The point where the line crosses the x-axis is the isotonic point. This is where no osmosis is taking place, i.e. no water is moving in or out of the potato. The next point, 0.25 molar looses approximately 4.0g. This shows that the water potential of the salt solution in the beaker is weaker than that of the potato chip. The next, 0.50 m, looses approximately 8.0g in mass. This shows that the salt solution has an even weaker water potential than 0.25 m and that osmosis took place. This is why the potato lost even more mass, and it shows that the water potential in the beaker is less than that of the potato chip. Also that the potato is trying to make the water potential of the fluid on both sides of the semi permeable membrane the same, (osmosis from the potato to the salt solution, from a higher water potential to a lower one). This pattern carries on through the graph, and even more mass is loss, as more water moves out of the potato. My results tally with my initial predictions. These were that osmosis would take place, and as the water potential decreases, morality increases, the percentage change in mass will decrease.

Evaluation