Method
Apparatus
- Boiling Tubes x 6
- Sugar Solutions x 6
- Measuring Cylinder
- Test Tube Rack x 2
- Knife
- Ruler
- Cutting Tile
- Cork Borer
- Cloth
- Beaker
- Scales
- Labels x 6
- Stop Watch
Plan
We have decided that we are going to use a range of solutions that will make ourselves (0.1, 0.2, 0.4, 0.6, 0.8, 1.0 molar solutions). The method we will use is shown in our theory. We are going to cut up the potato into six pieces of the same size, so that the potato will have roughly the same surface area. It is important that they have the same surface area because this affects the rate of Osmosis and as they are only in the water for 15 minutes (5 minutes in water & 10 in the solution), it is important that none of the potatoes have an unfair advantage. We will try to get all of the samples from the same potato so that there is no difference in the amount of sugar in the potatoes before we start the test. After doing a pre-test we decided that in the main test we would soak the potato samples in water before putting them in the solution because they were shown signs of dehydrating. This would help us to get more accurate results.
Fair Test
There are a number of things to consider that could affect the results of the test giving us unreliable results. The first thing is we will try to get all our samples from the same potato so there is no difference in the amount of sugar in the potato before the test starts. We will try to keep all the potato samples to the same length (5cm), as this is the best indication to the surface area of the potato. It is important that the whole potato is covered by the water as this will affect the surface area and the rate of osmosis occurring. The weights of the potatoes have to be as accurate as they can be to show any little differences in the weights as these could turn out to make a big difference when it comes to drawing up our graphs. To make sure any moisture left on the scales is not affecting the results we will wipe the top and reset the scales after each potato. It is important that we start and stop the stop watch as quickly as we can because as the potatoes are only in the solutions for a short time, even if one potato was in the water for a few seconds more than the others this would affect the results.
Safety
In any experiment safety is an important factor even if the experiment seems to be harmless. In our experiment we will be using shape tools such as knife’s and cork borers. It is important that when using any of these tools that they are used on a cutting tile. Remember not to run in the science lab especially when holding boiling tubes. When doing any experiment it is important that you follow all the rules such as packing away any books not being used, pushing the stools under the benches, removing all blazers and tucking in ties.
Method
I believe that this will be a relatively easy experiment to carry out. The first thing to do is to cut the samples from the potato, trying to waste as little as possible. All of the samples have been measured to 5cm (it is important that they are the same length so that they have the same surface area, allowing the same amount of osmosis to occur). When all six samples have been cut and measured they are put into soak in tap water for five minutes to stop them from dehydrating. After five minutes take them out of the water and weigh each of the potatoes, using a cloth to wipe off any excess water on the outside of the potato before weighing. While the potato is being weighed some one else should set up the boiling tubes in the test tube rack, each one with 30mls off a different molar solution. Put the potatoes into the solutions and start the stop watch. After the ten minutes is up, take all of the potatoes out of the boiling tubes and dry them off with the cloth to remove any excess solution again before weighing the potatoes to get the results off the test. In the main test this must be repeated three times. It is important that the test is repeated three times so that the results are more reliable and we can use them eliminate any anomalous data. This also helps us to make it a fair test.
Obtaining evidence
After the potatoes have been in the water for the set amount of time, they are removed, any excess water is removed and they are weighed. It is important that they are dried because there will be water on the outside that has not yet been absorbed by the potato and this therefore should not be counted in the experiment. The samples must be moved quickly to the scales as they will be losing water through evaporation. After each potato has been weighed the scales have to reset so that no moisture has been left on the scales and it cannot affect any potatoes that will be weighed after.
Results
Results
I have made a table of results that I collected from the experiment that we have just completed. There are four columns for each of the three tests we did. They are the before weight, after weight, difference and percentage difference. All the weights used and shown in the results are measured in grams too two decimal places. I will also work out the averages of all the tests as this will give as the best indication as to the actual amount of osmosis that has taken place. The formula that I will use to calculate the difference as a percentage is weight increase/decrease divided by the original weight multiplied by a one hundred.
Tables
Graphs
I have made up a graph on the next page showing the average result from the experiment. I have used the averages table shown above to make this table. After looking at the tables I have chosen to ignore some anomalous data. This is because it did not fit in with the other results I had and could lead us to the wrong conclusions when examining the graph. The table shown above does not included the data that I have chosen to leave out.
Conclusion
I think that although not all of the results were accurate, I know have enough evidence to prove my prediction rite. Overall I was happy with the way we conducted the experiment until I looked at the results more closely. The only thing that we did different from the plan was that we had to use two potatoes because we couldn’t get the 5cm samples from one potato. From looking at the tables I can see that there is only a limited link between all the tables and all of the data because some of data is anomalous. This means that none of the tests were entirely accurate. I think that the most accurate results I got were from my first test. In the table I excluded what I thought were anomalous results and used the averages of the results left over to try and make it as fair as possible (I have highlighted the results not included in their tables). After excluding some data the graph that I got looked a lot better. It has a smooth continuous line witch means that there is no longer any anomalous data. You can tell from the graph that the mid point, where the amount of sugar in the potato is the same as the amount in the solution, is some where around 0.45 molars. You can also tell that the potato can absorb water faster than it release’s it but to be sure of that we need to do other tests with different solutions, such as a 2 molar solution.
Evaluation
As I said before, I thought that the experiment went to plan. We stuck to the plan that we had, apart from getting all the samples from one potato, but every thing else went quite smoothly. There were a number of possible reasons as to why not all of our results were correct. It was possible that some of the potatoes may have had a larger surface area and therefore allowed more osmosis to take place in that short amount of time. I think that the results would have been more accurate if the potatoes had been left in the solutions for more than 10 minutes. If they had been left in for a longer time such as an hour, then there would have been bigger changes in weight and therefore the results would have been easier to analyse. Also if we had had better scales such as scales that went to more decimal places then the measurements that we took would have been more accurate. We could have done more tests or worked with other people or as a class, then share our results. This would make the results more accurate and more reliable. If we did the test again I would make the potato samples smaller so that the all the samples could be obtained from the same potato, this could have affected our results because potatoes that grew in different areas are unlikely to have the same amount of sugar in them. In future tests it would be better to try different vegetables or fruit, and try using sugar for example, to see if different things react differently with other substances dissolved in water.
Christopher Pummell 10.4 Cand No. 4419 Osmosis Coursework
