Four different concentrations of sugar solution were tested: 0M (distilled water), 0.3M, 0.6M, and 0.9M. Four potato chips were cut to 50mm, at an angle so that they could be measured before and after the experiment without mixing them up.
Four test tubes were used: one for each of the different solutions used. A chip was placed in each test tube and left for 30 minutes. After the 30 minutes, the chips were removed from the test tubes and their new lengths and changes in length were recorded.
Results:
Table of Class’s Results
N.B. The highlighted results are anomalous and have been discounted when calculating the average.
Table of Averages
Graph:
Graph showing the Percentage Change in the Length of Chip against Concentration
Conclusion:
From the results it is evident that when the chip is placed in distilled water, it increases in length, as water diffuses into the chip. The cells of the potato chip have become turgid and gained in size and volume, as they have gained water. However, when the chip is placed in the sugar solutions, it loses water by osmosis and decreases in length. The cells of the potato become flaccid and smaller, decreasing in volume, as they have lost water. In the sugar solutions, the chips lost water, because there was a higher concentration of water particles in the chips than in the sugar solution and so the chip lost water by osmosis to gain a balanced concentration gradient. The higher the concentration of the sugar, the more water was lost by the chip, due to the fact that the concentration gradient was steeper.
Evaluation:
The biggest problem is the fact that there were a couple of anomalous results in the class table. These anomalous results could have been caused by human error; for example the students may have measured their chips wrong or put the chips in the wrong solutions. To improve upon this, the tests could have been repeated so as to remove any anomalies. One other small problem was the fact that the chips may not have all been measured completely accurately (again due to human error).
Plan
In order to carry out the experiment, the following equipment will be needed: 6 petri dishes, 18 potato chips, a stopwatch, 6 different sugar concentrations (0M, 0.2M, 0.4M, 0.6M, 0.8M, and 1.0M), a small blade, and a balance precise to 2 decimal places.
The equipment will be set up as follows:
Table displaying how the final concentrations were achieved
After 4 hours, the new masses of the potato chips will be measured using the balance which is accurate to 2 decimal places of a gram. From the new masses, the percentage changes in mass will be measured and recorded in a results table. There will be 18 results in total: there will be 6 different concentrations, each of which will be repeated 3 times. The 6 concentrations will be: 0M (distilled water), 0.2M, 0.4M, 0.6M, 0.8M and 1.0M. Due to the fact that there will be so many results, it should be unnecessary to carry out any further repeats. However, if there were a number of anomalous results it would be useful to repeat the experiments in which they occurred.
Some changes were made from the method used in the preliminary experiment. It was decided that it would be necessary to produce more results in order to achieve a more accurate average, and so that there would be a wider spread of data and any anomalies could easily be identified. As opposed to using just 4 different concentrations, 6 different concentrations were to be used, and instead of only doing the experiment once, it would be repeated 3 times. In order to make the experiment more accurate, the change in mass will be measured as opposed to the change in length. This is because it is very difficult to measure all the chips to the same length, whereas if the change in mass is being measured, then the percentage change in mass can be found. The mass could also be much more accurately measured than the length, due to the use of the balance which is correct to 2 decimal places, and the results therefore should be more accurate.
The following factors might affect the results of the experiment: the temperature, the volume of the liquid, the surface area of the chip, and the concentration of the liquid. In order to ensure a fair test, these factors must be the same for each experiment (except for the concentration, as this is the variable being used in this experiment). Temperature will affect the rate of osmosis, because as it increases, the molecules move quicker and react quicker. To make sure that the temperature does not become a factor on the rate of osmosis, all the experiments will be at the same time so that any change in temperature that may occur during the experiment, will affect all of the experiments, canceling each other out. The volume of the liquids used could affect the rate of osmosis, as the more of the liquids there are, the more molecules there will be and the quicker osmosis will occur. The volume of the liquids used will be kept the same (50 ml). This will be carried out accurately, as the solutions will be measured carefully using measuring cylinders. Surface area affects the rate of osmosis, in that as the surface area increases, so does the rate of osmosis. This is because there are more cells in the potato and therefore more water to osmose. It does not matter that the surface areas of the chips will vary, due to the fact that it is the percentage change in mass that is being measured. The concentration of the liquid is the variable being used in this experiment, and the different concentrations being used are: 0M (distilled water), 0.2M, 0.4M, 0.6M, 0.8M, and 1.0M.
Results Table 1
From the results, a table showing the percentage change in mass could be produced. This is displayed below.
Results Table 2
From the results, a graph displaying the averages against concentration, and a graph showing the spread of the data could be produced.
Analysis
The results show that as the concentration of the salt solution increases, the percentage change in mass decreases. From the graphs it is visible that to start off with, between the concentrations of 0M and 0.4M, the decrease is very steep, but as the concentrations get higher, the lines of the graphs start to level out.
The reason why the percentage increase in mass got lower as the concentrations got higher (from 0M to 0.4M) was due to the fact that there was less water in the higher concentrations of the salt solution, and so less water had to osmose into the potato chips in order to level the concentration gradient. When the concentrations got even higher (from 0.4M to 1.0M) and water began to osmose from the potato chips into the salt solutions and the masses of the chips consequently decreased, the percentage decrease in mass of the chips got higher, as the concentrations got higher. This was because as the concentrations got higher, the concentration gradient became steeper and more water had to osmose in order to level it out.
The results prove the prediction made at the start of the investigation correct because, as predicted, for the lower concentrations the chips did increase significantly in mass and as the concentrations got higher the increase in mass would get smaller until the mass would begin to decrease. This occurred at the 0.4M concentration, and as the concentrations got even higher, the decrease of the mass of the chips got higher (as predicted). However, I failed to predict the shape of the graph that would be produced from the results and that the graph’s line would level out at the end (when the concentrations were at their highest).
Evaluation
The investigation went very well, for a number of reasons, as the results proved the hypotheses correct. Enough data was produced, as displayed in the graph, in order to obtain accurate results and formulate a conclusion. Fortunately, there were no anomalous results in the data; although if there had been, they would have been discounted when calculating averages. The fact that there weren’t any anomalies proves that the experiment was carried out carefully and to a suitable degree of accuracy. The fact that the results are not widely spread also proves this and strongly suggests that the results are accurate enough to support the above conclusion.
However, there could be a few improvements to this experiment to obtain even more accurate results. Firstly, even more results could have been obtained: the “in-between” concentrations (i.e. 0.1M, 0.3M, 0.5M, 0.7M, and 0.9M) could have been investigated; and a couple more repeats could have been done (to get an even wider range of results). The temperature could also have been carefully monitored (perhaps through using a water bath) so that it did not affect the osmosis rate. There may also have been very slight anomalies that could have occurred due to human error. For example, the measuring of the liquids may not have been entirely accurately done (especially considering that no burettes or pipettes were used to measure out the quantities of the liquids); or the masses of the chips could have been recorded slightly incorrectly. Despite these improvements that could be made, overall the investigation was carried out carefully and accurately; and because of this, a good set of results that prove the hypotheses correct have been obtained.
In order to produce further work to provide additional relevant evidence, more procedures could be carried out. One could investigate the effects of the other factors that affect the rate of osmosis (i.e. surface area, temperature, and the volume of the liquids used). The potato chips could be cut to different sizes, so that they would have different surface areas and the effects of this on the osmosis rate could be investigated. In order to discover the effects of temperature on the osmosis of the potato chips in the salt solutions, the experiment could be carried out in different temperature conditions. To achieve this accurately, a water bath could be used, but would still have to be monitored carefully to ensure that the temperature is remaining the same. The effects of using different volumes of the liquids could also be investigated. To carry this out, the experiment would be carried out much the same as before, but different amounts of the liquids could be used. To ensure accurate results, the volumes would have to be measured carefully using burettes and pipettes.