Method
The 2 beakers are filled to equal amounts of water (250ml) for a fair test. Then we weighed and measured the potato for equal surface area and size.
Then we filled one of the beakers water with 3 spatulas worth of salt. That then became the salt solution of the two. Then at the same time we placed the two bits of potato into their respective solutions and began the timer. After 5 minutes we took the bits of potato out of their respective solutions and weighed and measured them. The results are as follows:
The results above prove my prediction that in water the mass and size of the potato will increase and in the salt solution the mass and size of the potato will decrease.
Pre test #2
In this I will try to prove my prediction that the higher the concentration in the beaker the potato’s mass and size will decrease and the lower the concentration in the beaker the potato’s mass and size will increase.
Apparatus:
- 3 x boiling tubes – test tubes would be impractical.
- 3 x measuring cylinder – to get the same amount of water for each boiling tube. And for a fair test.
- 1 x test tube rack – to put the boiling tubes in.
- 1 x spatula – to get salt from the salt container into the solutions.
- 3 x bits of potato – equal size and mass measured and weighed before experiment and the results recorded to be able to compare after the experiment.
- 1 x timer – so wee know when the 10 minutes are up.
- 1x scales – to weigh the potato and find out its mass.
- 1 x ruler – to measure the size of the potato.
- 1 x blunt knife – to cut the potato into equal sizes (so surface area isn’t affected).
Method
We measured out 100ml in the measuring cylinders to put in the boiling tubes, after putting the water into the boiling tubes we placed them into the test tube rack. We had measured out 100ml for each boiling tube because we wanted it to be a fair test. Then we cut up and measured the two bits of potato that were going into the boiling tubes. They were equal mass and length for as fair test. Then we added the salt to one of the solutions (2 spatulas worth) and sugar to another (2 spatulas worth). We then placed the potato in their respective solutions, and started the timer. After 10 minutes we took the pieces of potato out of the solution and weighed and measured them. The results are as follows:
As you can see from the results my prediction was disproved. Instead of losing weight and decreasing in size the two concentrated solutions (sugar and salt solutions) they increased in size and weight. This is quite irregular considering what my prediction said and what previous science has dictated. Why has this happened? Maybe the 2 spatulas worth of salt and sugar weren’t enough and we needed a more concentrated solution – maybe 3 or4 spatulas worth was needed. Maybe we needed to leave it in there for longer as 10 minutes might not have been enough (although in our last pre test it proved my prediction and only 5 minutes was needed). Maybe we weighed and measured them wrong although that seems highly unlikely, yet for our next test we must make sure to weigh and measure the pieces of potato properly.
Pre test #3
In this I will try to prove my prediction that the higher the concentration in the beaker the potato’s mass and size will decrease and the lower the concentration in the beaker the potato’s mass and size will increase.
Apparatus
- 6 x boiling tubes – test tubes would be impractical.
- 6 x measuring cylinder – to get the same amount of water for each boiling tube. And for a fair test.
- 1 x test tube rack – to put the boiling tubes in.
- 1 x spatula – to get salt from the salt container into the solutions.
- 6 x bits of potato – equal size and mass measured and weighed before experiment and the results recorded to be able to compare after the experiment.
- 1 x timer – so wee know when the 5 minutes are up.
- 1x scales – to weigh the potato and find out its mass.
- 1 x ruler – to measure the size of the potato.
- 1 x blunt knife – to cut the potato into equal sizes (so surface area isn’t affected).
Method
The technicians in the prep rooms had already made us 3 slat solutions worth: 0.25%, 2% and 5%. We had to make 5 solutions of different concentrate salt and 1 solution of pure water. We only had 3 solutions of salt and we needed 5 so we halved the 5% and the 2% to give us 2.5% and 1% concentrate solutions. We halved them by measuring out 50ml of the given solution .e.g. 5% and then we added 50ml of water to dilute it, so it was 50ml salt concentrate and 50ml water. After doing this and putting the solutions into the boiling tubes we cut up, weighed and measured 6 pieces of potato that were going into the boiling tubes. Equal size and mass to keep it a fair test, this we have had to do on all as a fair test is very important. Then we placed the pieces of potato into their respective solutions and started the test. Sadly we never finished the test as lesson time ran out. But the above method will be the method used when we do the real experiment after the half term.
Proper Experiment
In this I will try to prove my prediction that the higher the concentration in the beaker the potato’s mass and size will decrease and the lower the concentration in the beaker the potato’s mass and size will increase.
Apparatus
- 6 x boiling tubes – test tubes would be impractical.
- 6 x measuring cylinder – to get the same amount of water for each boiling tube. And for a fair test. 25 ml for each boiling tube.
- 1 x test tube rack – to put the boiling tubes in.
- 1 x spatula – to get salt from the salt container into the solutions.
- 6 x bits of potato – equal size (for a fair test as surface area is a factor that effects osmosis – we only want to change one factor, the concentration) measured and weighed before experiment and the results recorded to be able to compare after the experiment.
- 1x scales – to weigh the potato and find out its mass before and after the experiment so that we can compare the results to find out how much osmosis has occurred.
- 1 x ruler – to measure the size of the potato.
- 1 x blunt knife – to cut the potato into equal sizes (so surface area isn’t affected).
Method
The technicians in the prep rooms had already made us 3 slat solutions worth: 0.25%, 2% and 5%. We had to make 5 solutions of different concentrate salt and 1 solution of pure water. We only had 3 solutions of salt and we needed 5 so we halved the 5% and the 2% to give us 2.5% and 1% concentrate solutions. We halved them by measuring out 12.5ml of the given solution and then 12.5 ml of water. E.g. 5% salt solution, then we added 12.5ml of water to dilute it, so it was 12.5ml salt concentrate and 12.5ml water. After doing this and putting the solutions into the boiling tubes we cut up, weighed and measured 6 pieces of potato that were going into the boiling tubes. Equal size to keep it a fair test, this we have had to do on all as a fair test is very important. Then we placed the pieces of potato into their respective solutions and started the test.
The following day we took the pieces of potato out of their solutions. We weighed and measured them to see if there had been any osmosis occurring in the solutions. The results are on the following page:
As you can see from our experiment it almost proves my prediction that the higher the concentration in the beaker the potato’s mass and size will decrease and the lower the concentration in the beaker the potato’s mass and size will increase.
However it does not totally prove it. The percentage change in size is fine, you can see that as soon as salt is added in the solutions the size decreases as predicted. However, in the percentage change in mass results the percentage change doesn’t start to fall (and therefore its mass is decreasing) up until 1% salt concentration which is a high level of concentrate and it is strange that it should fall here and not as soon as it gets to 0.2% salt concentrate. This means that the concentrate of the salt inside the potato’s cell’s cytoplasm is very high – sadly, it could have just been a dodgy potato as the potato’s we use come in a randomly selected pack (not different types; as this would contradict a factor in osmosis and would not make the experiment fair – all the same type but that doesn’t mean their chemical structure is the same). Or we could have not left the potato in the solution for long enough, causing our results to be what would happen prematurely. To make sure we haven’t done anything wrong in terms of human error in measuring the potato or anything like that we will conduct a repeat experiment.
Repeat experiment
This experiment will try to be exactly as the proper experiment was so we get the most fair and accurate results.
Apparatus
- 6 x boiling tubes – test tubes would be impractical.
- 6 x measuring cylinder – to get the same amount of water for each boiling tube. And for a fair test. 25 ml for each boiling tube.
- 1 x test tube rack – to put the boiling tubes in.
- 1 x spatula – to get salt from the salt container into the solutions.
- 6 x bits of potato – equal size (for a fair test as surface area is a factor that effects osmosis – we only want to change one factor, the concentration) measured and weighed before experiment and the results recorded to be able to compare after the experiment.
- 1x scales – to weigh the potato and find out its mass before and after the experiment so that we can compare the results to find out how much osmosis has occurred.
- 1 x ruler – to measure the size of the potato.
- 1 x blunt knife – to cut the potato into equal sizes (so surface area isn’t affected).
Method
The technicians in the prep rooms had already made us 3 slat solutions worth: 0.25%, 2% and 5%. We had to make 5 solutions of different concentrate salt and 1 solution of pure water. We only had 3 solutions of salt and we needed 5 so we halved the 5% and the 2% to give us 2.5% and 1% concentrate solutions. We halved them by measuring out 12.5ml of the given solution and then 12.5 ml of water. E.g. 5% salt solution, then we added 12.5ml of water to dilute it, so it was 12.5ml salt concentrate and 12.5ml water. After doing this and putting the solutions into the boiling tubes we cut up, weighed and measured 6 pieces of potato that were going into the boiling tubes. Equal size to keep it a fair test, this we have had to do on all as a fair test is very important. Then we placed the pieces of potato into their respective solutions and started the test.
The following day we took the pieces of potato out of their solutions. We weighed and measured them to see if there had been any osmosis occurring in the solutions. The results are on the following page:
As you can see from our results we have another irregularity! On the 0.5% salt concentrate the mass before and after the experiment was the same and there was a very slight percentage change in the percentage change in size column. This means that there was exactly the same concentrate of salt inside the potato’s cell’s cytoplasm! However all the other results correspond with our prediction that the concentration in the beaker the potato’s mass and size will decrease and the lower the concentration in the beaker the potato’s mass and size will increase. As predicted, as soon as salt is in the solution the potato’s mass and size starts to decrease – also they decrease in accordance with their amount of concentrate. I.e. the higher the concentrate the more osmosis is taking place (apart from the anomaly of the 0.5% salt solution). Sadly we don’t have enough time to conduct another repeat experiment to see if we can prove better our prediction.
Evaluation
I do believe that we have set out what we wanted to achieve. I am confident that my results were accurate and that I took enough of them so that my results are reliable. I believe my results are accurate because I used:
- A measuring cylinder which had measurements of millimetres so that we could get it accurately.
- The scales we used to weigh and find out the mass of the potato pieces had an accuracy of 2 decimal places.
- We left the experiment over-night so that there was more than enough time for a recorded change of osmosis in the potato.
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We used a ruler which had millimetre measurements on it and we measured to exactly 2.5 cm.
Improvement
- The water we used could have been pure water – not tap water that may contain chemicals which will affect the process of osmosis.
- We could have kept the temperature in the lab constant when we left them over night as the temperature fluctuated during the night (at night the temperature drops considerably) this may have affected the rate of osmosis.
Extension
- We could use a different substance in the water to make the solution such as sugar or even pepper.
- We could use another type of food or vegetable, like a carrot to see if we get the same results as the potato.
- We could also find the amount of concentration of salt in the potato by fine tuning the solution outside the potato.
- We could increase the amount of concentrations from six to ten solutions in order to get more results and therefore more reliable results that could prove/disprove my prediction that the higher the concentration in the beaker the potato’s mass and size will decrease and the lower the concentration in the beaker the potato’s mass and size will increase.
