The Effect of Sodium Chloride on a Potato Chip

The Effect of Sodium Chloride on a Potato Chip
To investigate what happens to a potato chip?s weight when placed in different concentrations of Sodium Chloride introduction:~ ====== Osmosis is defined as ?the movement of water molecules from an area of high water concentration to an area of low water concentration, across a semi-permeable membrane? (Collins, 1999). A semi-permeable membrane is a membrane that partially allows liquid to pass through. In the case of the experiment I am carrying out, the potato chips have small holes in their membranes, which only lets some water molecules flow in and out of the solution and potato chips depending on the concentration of both. In a high concentration of water the amount of solute (e.g. salt) is low. This would be called a weak or dilute solution. In a low concentration of water the amount of solute (e.g. salt) is high.
This would be called a strong or concentrated solution. When two such solutions are divided by a semi-permeable membrane the water will move from the area of high concentration to the area of low concentration, until both sides are equal or have reached ?equilibrium?. [image] [image] [image] [image] [image] Dilute Solution Concentrated Solution Semi-permeable membrane Text Box: Water Molecule Text Box: Sodium Chloride Molecule Plant cells always have a strong cell wall that surrounds them. When osmosis takes place, and they soak up water, they start to swell. However the cell wall stops them from bursting as it is made from cellulose, which is very strong. When plant cells are put into dilute solutions they become ?turgid?, which means hard. Turgidity is important in plants, as it is this what makes plant stems strong and upright. Pressure inside the cell (when in dilute solutions) rises, and eventually this pressure is too high that no more water can enter the cell. The potato cells would increase in length, volume and weight because of the extra water. When plant cells are put into concentrated solutions they lose water by osmosis and become ?flaccid?, which means the opposite of turgid - limp. The contents of the potato cells shrink and pull away from the cell wall. These cells are said to be ?plasmolysed?. When plant cells are put into solutions that have the same osmotic strength as the plant cells, they are in a state between turgidity and flaccidity. This is called ?isotonic?, meaning equal. The potato cells will have decreased in length, volume and weight. variables:~ To create a fair experiment, I am going to use 3 different variables:
The Independent Variable
The Dependant Variable
The Fixed Variable
The independent variable is the factor that I am going to change. I will change the concentrations of solution. The different salt concentrations will be changed so that I can see the difference of the potato chips when placed in different molarities (strengths) of NaCl. The dependant variable is the factor that I will measure. I will measure the weight change of the potato chips before and after being placed in different molarities of salt solutions. I will measure this by using an electronic scale. The fixed variable is the factor that I will keep the same. I will keep the amount of solution I put into the beakers for each experiment the same by using a measuring cylinder. hypothesis:~ I predict, that as the concentration increases, the weight of the potato chip will decrease. My reasoning behind this, is that the higher the concentration of salt in a solution, the lower the concentration of water. When the potato chip is put into the solution, it will, by osmosis lose some of its water, and the water will diffuse into the solution of salt, causing the potato chip to lose water, thus decreasing in weight. I am going to perform my experiment using 5 different concentrations of NaCl. These will be 1M, 0.5M, 0.25M, 0.125M and 0.625M. I will repeat this 3 times to make sure that it is a fair test and so that I can obtain accurate results. When I put the potato chip into:
The concentrated solution (1M NaCl) I will expect the chip to
decrease a lot in weight
The isotonic solution (0.5M NaCl) I will expect the chip to stay
roughly the same in weight
The solution of 0.25M NaCl I will expect the chip to increase
slightly in weight
The solution of 0.125M NaCl I will expect the chip to increase more
in weight
The dilute solution (0.625M NaCl) I will expect the chip to increase
a lot in weight.
apparatus:~ 5 Beakers Labels NaCl Solution (1M) Distilled Water Measuring Cylinder (x2) Potato Chips (x15) Electronic weighing scales planned method:~ A range of salt solutions in the 5 beakers will be arranged with the concentrations, 1M, 0.5M, 0.25M, 0.125M and 0.625M. Adding varying amounts of distilled water to the solutions using a measuring cylinder will change the strength of the solutions. On each of the beakers a label will be put on labelling the contents. Then a potato chip will be weighed then put into each beaker. The potato chips will stay in the different solutions for 2 hours, and then they will be taken out and weighed. I will repeat this 3 times to achieve accurate results. method:~ 1. I set up 5 beakers and lined them side-by-side. 2. Using a measuring cylinder I poured 60ml of NaCl (1M solution) into the first beaker. 3. I used the same measuring cylinder to pour 30ml of NaCl from the first beaker into the second beaker. Into this beaker I poured 30ml of distilled water using the second measuring cylinder. The second beaker now contained 0.5M of NaCl. 4. I repeated method no.3 (beaker 3 would have 0.25M of NaCl and beaker 4 ? 0.125) until all five beakers had solution in. As the last beaker (beaker 5), had 60ml of solution whereas the others had 30ml because they had another beaker to put the other 30ml into, I poured out 30ml using the first measuring cylinder and emptied it down the sink. This beaker now contained 0.625M of NaCl. 5. I used the labels to write down each molarity of the solutions in the beakers and stuck them on each beaker so that I knew which one had what strength solution in it. 6. I then took 5 potato chips and weighed each one using the electronic weighing scales. I recorded the results. 7. I placed each potato chip into a different concentration of salt. 8. After 2 hours, I took the potato chips out of the solutions, shook off the excess liquid, and measured them again using the scales. I recorded the results. 9. After doing this, I repeated method 1-8 twice (using the remaining ten potato chips) to get accurate results. results:~ 1ST concentration (M) before (g) after (g) percentage change IN mass (%) 1 3.94 3.40 -13.71 0.5 3.70 3.23 -12.70 0.25 4.17 4.03 -3.36 0.125 3.75 3.83 +2.13 0.625 3.93 3.96 +0.76 2ND concentration (M) before (g) after (g) percentage change IN mass (%) 1 3.46 2.51 -27.46 0.5 3.14 2.42 -22.93 0.25 3.94 3.67 -6.85 0.125 3.37 3.45 +2.37 0.625 3.25 3.24 -0.31 3RD concentration (M) before (g) after (g) percentage change IN mass (%) 1 3.35 2.64 -43.28 0.5 3.29 2.56 -22.19 0.25 2.94 2.71 -7.82 0.125 3.45 3.52 +2.03 0.625 3.37 3.55 +5.34 average concentration (M) 1. percentage change IN mass (%) 2. percentage change IN mass (%) 3. percentage change IN mass (%) avg. percentage change IN mass (%) 1 -13.71 -27.46 -43.28 -28.15 0.5 -12.70 -22.93 -22.19 -19.27 0.25 -3.36 -6.85 -7.82 -6.01 0.125 +2.13 +2.37 +2.03 +2.18 0.625 +0.76 -0.31 +5.34 +1.93 conclusion:~ My graph shown on the previous page shows the line of best fit for the percentage change in mass of the potato chips over the course the two-hour experiment. The graph is a curve that slopes downwards and does not go through the origin. As the line is not straight and doesn?t pass through the origin, it means that the percentage gain and loss in mass and concentration are not directly proportional to one another. However I have noticed a pattern on my graph. As the concentration of the solution increases, the percentage change in mass decreases. My graph proves that my prediction was right. It shows that the potato cells increase in mass in solutions with a high water concentration and decrease in mass in solutions with a low water concentration. This graph of the change in mass helps prove the point of complete plasmolysis, whereby the potato cannot expand and take in any more water. On the graph the molar concentration increases as the change in mass decreases. From right to left the first three points on the graph are very spread out indicating that there was a large change in the mass. This decreases throughout the increasing molar concentration until the change is very small. A solution in which the concentration of salt is greater than that inside the cell is called a Hypertonic solution and will cause a cell to become plasmolyzed. An example of this in my results is the test using 1M of NaCl. It becomes dehydrated and loses water through plasmolysis. If the concentration of the salt solution outside the cell is less than that inside the cell, it means that the solution is Hypotonic to the cells of the potato chip. The water will diffuse into the cells, making it turgid. This would explain why potato chips put into a solution of 0.625 molar seemed very firm compared to the potato chip used for 1 molar, this was because the cells of the potato had lost their turgidity, and had become flaccid [image]To conclude I can say that the movement of water through a semi-permeable membrane is affected by the concentration of a salt solution, or by any other solution. The higher the concentration of the salt solution, the more the potato chip will lose its weight, width and length. [image] osmosis diagram [image] evaluation:~ I found my results to be fairly accurate as they followed my prediction. I say fairly accurate, because while plotting the results onto my graph I came across an anomalous result, which I have circled on it. If I were to repeat the experiment again I would repeat the investigation more than three times. I thought that the range of concentrations that I used were sufficient, although if I repeated the experiment I would use more concentrations to enable me to obtain more diverse results, for example 0.10M, 0.15M and 0.20M. This would have given me a more accurate insight into the osmosis going on in the potato chips. When I removed the potato chips from the beakers and shook off the excess water I may not have taken enough water off of it before I weighed it. As the electronic scales are very accurate, they would have measured the excess water on many of the potato chips which would have added to their ?after? weight. If the experiment was repeated I could find another way to dry the potatoes that would ensure that all were dried in the same way for the same time, which would also not deduct the potato chip?s own water inside it. Having said all of the above I think that the experiment was successful and I was very pleased with the comparison of my results with my initial prediction.

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