Hypothesis:- I predict, that as concentration increases, the weight and length of the potato chip will decrease. My reasoning behind this, is that the higher the concentration of glucose 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 sucrose, causing the potato chip to lose water, thus decreasing in weight and length. However, if a potato chip is placed into a solution of 0 molar concentrations, it should gain weight, width, and length. This is because the solution has more water potential (its molecules’ ability to move) than the potato chip, and so water moves from a region of high concentration (the solution) to a region of low concentration (the potato chip.)
Variables:-
Independent Variable:
- This is the concentration of sucrose solution in mol/litre; this is the only thing in the experiment that will change.
Dependent Variable:
- The mass of potato chip
- The length of the potato chip
- The width of the potato chip
Control Variables:
- The mass of potato chip will be the same at the start of the experiment.
- The size of the chip will be the same at the start
- The surface area will be the same so there is the same potential for collisions.
- The temperature in the room will be constant, as temperature may affect the rate of osmosis.
- The freshness of the potato chip, as a rotten potato may not absorb as much water.
- The same potato will be used so we can grantee that the rate of osmosis has the potential to be the same.
Fair Test: - For a fair test the independent variable will be the only one that will change and the dependant variables will be the same at the start of the experiment, this will be as accurate as can be in the lab.
Equipment:-
- Stop Clock – to time our experiment
- Cutting tile – to cut the potato on
- Knife – to cut the potato on
- Measuring Cylinder – to measure the amount of solution we use
- Distilled Water
- Sucrose Solution
- Scales – to weigh the potato chips after they have been in the Petri dish.
- Ruler – to measure the length of the potato chips
- Cork borer – to cut out the potato chips.
- Petri Dishes – to leave the chips in their solution
Method:
- Collect all the equipment needed.
- Use the borer to cut out potato cylinders.
- Cut them into twelve pieces.
- Weigh the cut potato chips on the accurate balance and record the results on a table.
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Measure 25cm3 of all the solutions of sugar (0.0, 0.2, 0.4, 0.6, 0.8, 1.0 Molar) and place them into the petri dishes.
- Place two potato chips in each petri dish.
- Leave all the petri dishes containing the potato chips and solutions in the same place for three days.
- After three days measure and weigh the potato chips.
- Record the results.
- Repeat this process twice for accurate results.
Safety: To carry out this experiment safely I will not pour the solutions from a high height and use the cork borer and knife safely keeping them away from the edge of the table.
The table my results will be recorded on will look similar to this.
Results:-
Table 1: Initial
Table 2: After
Table 3: Percentage change in mass:
Table one shows what size and weight the potatoes were prior to placing them into the different sucrose solutions. Table two shows the after measurements. Table 3 shows the percentage change in mass, I used the following formula:
CHANGE IN MASS (g)
ORIGINAL MASS (g)
Table 4 shows the average of the change in mass in percentages.
Conclusion:-
From my results I have drawn a graph showing the effects of concentration on osmosis the graph shows a curve decreasing.
From the result and graph it can be seen that as concentration increases, the weight, of the potato chip will decrease. My reasoning behind this, is that the higher the concentration of glucose 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 sucrose, causing the potato chip to lose water, thus decreasing in weight.. However from my graph you can see, when a potato chip is placed into a solution of 0 molar concentrations, it has gained weight of an average of 56.35% whereas at 0.2 Molar and 1.0 Molar it decreases in weight and therefore all values are minus. This is because the solution has more water potential (its molecules’ ability to move) than the potato chip, and so water moves from a region of high concentration (the solution) to a region of low concentration (the potato chip.)
From the graphs it can also be seen the initial mass changes occur at a greater rate than the end ones for example, the percentage mass change for potato one between 0.0 – 0.2 mol/litre sucrose solution gives a 39.6% change in mass, between 0.2 – 0.4 mol/litre sucrose solution gives only a 9% change, between 0.4 – 0.6 mol/litre sucrose solution gives an 11.6% change and finally the percentage change in mass between 0.8 – 1.0 mol/litre sucrose solution is only 9.5%. In other words the fastest rate of decrease in percentage change occurs from approximately 0.1 – 0.4 mol/litre sucrose solution and is slower at the end. This is because they have a similar amount of water and sugar in the potato and in the petri dish.
My conclusion agrees with my prediction as water moves from a higher concentration to a lower concentration through a semi permeable membrane.
Evaluation: - Although the results obtained support my prediction there are several anomalous results. From my results I can see that repeated results at 0.6 and 1.0 Molar
were anomalous. This is also shown on my graph at 0.4 as that is where the curve breaks slightly. This could be due to the fact that the other variables were not kept constant. They could also have occurred because the potato from which the chips were taken from could be abnormal or different from the other chips. To minimise the number of anomalous results obtained the experiment could be improved by keeping the petri dishes in a water bath at a set temperature, by keeping them at a constant pressure, leaving the potato chips in the solutions for a longer time period to allow the solution to penetrate fully, carrying out the experiment with a greater number of concentrations and repeating it more times for each concentration of sugar solutions. The rest of the points on my graph are close to a curve line. Since most of my results were fairly accurate I can say with reasonable confidence that my results were valid. For further work to provide additional evidence I could repeat this experiment by using a greater range of solution strengths or using tissue samples from other plants to discover whether my prediction is true of other plant tissues and not only correct for potatoes. Also I could calculate the rate of diffusion by Fick’s law as it is used to measure the rate of diffusion. It states that:
(The symbol a means ‘proportional to’)
The larger the area and difference in concentration and the thinner the surface, the quicker the rate. Which could have given me a more precise result.
I would also take into account all the changes I have mentioned for my method e.g. keeping the petri dishes in a water bath at a set temperature, by keeping them at a constant pressure, leaving the potato chips in the solutions for a longer time period to allow the solution to penetrate fully, carrying out the experiment with a greater number of concentrations and repeating it more times for each concentration of sugar solutions