Investigating Osmosis In Potato Cells
Uploaded by mozilla on Feb 15, 2006 |
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Investigating Osmosis In Potato Cells
Apparatus:
The apparatus used in this experiment were: 1) 5 beakers, 2) 3 large potatoes (same type), 3) 15 pieces of potato without skin (roughly the same size), 4) 10 pins, 5) 50ml of distilled water, 6) 50ml salt solution 0.50, 7) 50ml salt solution 1.00, 8) 50ml salt solution 1.50, 9) 50ml salt solution 2.00 10) Scales, 11) Knife, 12) chopping board, 13) cork borer,
Prediction & Theory:
When the potato pieces are put in to the water there are more water molecules in the water then there is in the potato cells; therefore the water molecules move by osmosis into the potato cells through the membrane. This means that the mass of the potato piece will increase and the potato will feel harder.
When the potato pieces are put in to the salt water there are more water molecules in the potato cells then in the salt water; therefore the water molecules by osmosis into the water from the potato. This means that the mass of the potato piece will decrease, and it will feel really soft. The stronger the concentration of the salt solution the more it will decrease in weight.
Fair Testing:
The things needed to be kept the same during this experiment to make it a fair test are:
1) The amount of each concentration must be 50ml.
2) There must be 3 pieces of potato in each concentration.
3) The same potato must be kept the same.
4) They all have to be left for the same amount of time.
5) They all have to be washed to get rid of the dead cells.
Method:
Making sure that there is a chopping board down cut with a cork borer 15 pieces of potato, but make sure that there isn't any holes and that you cut of the dead skin and that all the pieces are roughly the same size. In 5 pieces of potato put a pin at the top end, in another 5 pieces of potato put a pin in the middle, and leave the last 5 without out. This is done so that each piece is easier to identify when weighing. Weigh each piece of potato and make a note wether is has a pin in and what concentration it's going in to. Fill 5 beakers with the 5 solutions (see apparatus), and then put 3 pieces of potato one with the pin in the top, one with a pin in the middle and one without in each of the beakers. Leave for about 3/4 hours so that osmosis can occur. After the period of time take out the pieces of potato from each solution one at a time wipe of the access water and weigh it, write down the result noting what the weight was and what solution it came from. Repeat this for all 15 pieces. Once that is done you can work out the difference in mass and also the percentage change.
Results:
Distilled Water:
Mass at Start (g) Mass at End (g) Difference in Mass % Difference
Pin at Top 4.51 4.81 0.3 6.7
Pin in Middle 4.4O 4.73 0.33 7.5
No Pin 3.21 3.39 0.18 5.6
Salt Solution 0.50:
Mass at Start (g) Mass at End (g) Difference in Mass % Difference
Pin at Top 3.91 3.55 -0.36 -9.2
Pin in Middle 4.23 3.85 -0.38 - 9.0
No Pin 3.99 3.4 -0.59 -14.8
Salt Solution 1.00:
Mass at Start (g) Mass at End (g) Difference in Mass % Difference
Pin at Top 4.43 3.79 -0.64 -14.4
Pin in Middle 4.81 4.2 -0.61 -12.7
No Pin 3.88 3.41 -0.47 -12.11
Salt Solution 1.50:
Mass at Start (g) Mass at End (g) Difference in Mass % Difference
Pin at Top 4.49 4.12 -0.37 -8.2
Pin in Middle 4.57 4.19 -0.38 -8.3
No Pin 3.86 3.29 -0.57 -14.8
Salt Solution 2.00:
Mass at Start (g) Mass at End (g) Difference in Mass % Difference
Pin at Top 4.54 4.19 -0.35 -7.7
Pin in Middle 4.6O 4.21 -0.39 -8.5
No Pin 3.89 3.37 -0.52 -13.4
Conclusion & Analysis:
My prediction for this experiment was correct. That the higher the concentration the faster the reaction will happen. This is because by increasing the concentration it increases the speed of the reaction. This is because the higher the concentration the molecules there are in the same volume of acid, so there are more collisions.
Evaluation:
In this experiment I tried to find out whether the prediction was right and it was. I think that some of the equipment was accurate in the investigation like when the stop watch was started, because when the stop watch has started and the rubber bung put on top some of the gas may have escaped. Also the carbon dioxide is soluble in water, so some of it will dissolve as it comes out of the delivery tube into the measuring cylinder.
When I repeated my results that most of them were close together either a few higher or lower, although a couple of the results for the 1.0m some of the results were quite far off. This may have been because some of the gas escaped from the beginning, or it wasn't read properly from the cylinder, but I don't think this could've been improved on.
I think that the experiment method was suitable but there could be another way of putting in the acid without the gas escaping as much as this method. Below is a diagram of another method which could've been used to do this experiment which may have produced more reliable results. |
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