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Factors affecting Osmosis in Potato Tissue.

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Vicky Scurr 19/5/02 Factors affecting Osmosis in Potato Tissue Background Scientific Information: Key Variables: There are several variables we must consider. These are: 1. Length of potato chip 2. Mass of potato chips 3. Temperature 4. Variety of potato 5. Volume of salt solution 6. Duration 1. We must keep the length of potato chip the same because if some are longer than others then they have a larger surface area which will affect the rate of osmosis. 2. We have to weigh the potato chips at the beginning of the experiment and at the end so that we can measure the increase or decrease in mass. 3. The temperature must be kept the same as an increase in temperature may increase the rate of osmosis. 4. The variety of the potato is kept the same because 5. We keep the volume of the salt solution the same because if there is less salt solution in some of them then 6. We keep the duration of each experiment the same to make sure the experiment is a fair test which is why we keep all the others the same as well. To make this experiment a fair test we can only change one thing. This is the concentration of the salt solution. This is the independent variable. Hypothesis: I predict that if we double the concentration of the hydrochloric acid then the reaction rate will double. We are going to use a range of 3 to 1 molar so we have two doubles which are 1 and 2 and 1.5 and 3. The results will be directly proportional. ...read more.


The concentration of the hydrochloric acid is the only thing that we change. 2. Temperature stays the same. 3. The volume of the acid stays the same. 4. The length and width and depth will all be the same, because we can measure the length and the width and depth will be the same because all our magnesium will be taken from the same roll of magnesium ribbon. 5. There will be no catalyst present. 6. We will have straight magnesium ribbon. Observations: We have drawn up the tables of the results we got from the experiments. We have also done graphs. The tables show the time against the volume of hydrogen, and the graphs show the same thing, with a best fit curve. We can see that when the curve on the graph goes up, the volume of the hydrogen is increasing, but the rate of reaction is decreasing. Results: Results table 1 (3 molar) Time (s) Volume of hydrogen (cm )1 2 3 average 2 50 59 48 52.4 4 71 84 66 73.7 6 85 92 99 89.7 8 88 95 97 93.4 10 91 95 98 94.7 12 91 95 98 94.7 Results table 2 (2.5 molar) Time (s) Volume of hydrogen (cm ) 1 2 3 average 3 37 53 46 45.4 6 79 84 79 80.7 9 95 91 90 92 12 100 94 95 95.8 15 100 95 95 96.4 18 100 95 95 96.4 Results table 3 (2 molar) Time (s) Volume of Hydrogen (cm ) 1 2 3 average 3 18 18 28 21.4 6 27 40 45 37.4 9 53 53 70 58.7 12 67 66 84 72.4 15 77 77 88 80.7 18 83 82 89 84.7 21 84 82 89 85.0 24 84 82 89 85.0 Results table 4 (1.5 molar) ...read more.


There are also two anomalies on the graph on which I plotted rate of reaction against concentration, at 1.5 molar and 2.5 molar on the x axis. These are dues to some sort of experimental error. Another reason is that possibly the concentration of the hydrochloric acid was slightly different each of the three times we repeated each experiment. With the highest concentrations of hydrochloric acid, the reaction was over very fast, and the initial rate, which is what we are most interested in, was so fast that it was hard to measure the volume of hydrogen collected at exactly regular intervals. We might have been a fraction of a second out and that would have made a lot of difference to each individual result. I think that it altogether the procedure used to carry out the investigation is quite accurate and suitable. There are thing which could have been done to improve it. There are many limitations to this experiment because it is difficult to be exact with such limited apparatus. It is difficult to put the magnesium into the hydrochloric acid at the same time as putting the bung in and starting the stop clock. This means that some of the magnesium may already have reacted with the hydrochloric acid before it was possible to put the bung into the side armed flask. To find out more relevant information, we could have used a wider range of concentrations as then we could have seen more proof of our prediction being partially correct. I think that altogether the results are quite good and accurate because I have so few anomalies, and this is proof that it is quite accurate, because we can see where the inaccuracies are (where there are anomalies) and there aren't many. ...read more.

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