The different beakers will receive different amount of salt:
100cm3 of water and:
0g 2g 4g 6g 8g of salt
To calculate:
% change in mass = change in mass (g) x 100
initial mass (g)
From the results received from the experiment, I will then plot a graph to locate the correct solution needed for Mrs. Chips chips. The concentration of solution is plotted against the average percentage change in mass.
If I use this method, I would expect to find that when concentration increases, the weight and length of the potato chip will decrease. When the potato chip is put into the solution, it will, by osmosis lose some of its water. I predict that through this experiment we will find a solution so that the potato chip will not lose or gain any water through osmosis and the concentration gradients are equal or at an equilibrium. As a prediction, I would guess this value would be approximately 0.1-0.2% of salt solution would be needed for no osmosis to occur in the cells.
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Recording of all the results is very important during this experiment to reach a conclusion. We need to record tables with the following information:
- Percentage salt solution
- Initial mass
- Final mass
- Change in mass (g)
- Change in mass (%)
- Average change in mass (%)
In the experiment I am using six different solutions three times. To make each solution different I will change to percentage of salt in the solution. This will give me a range of salt solutions for Mrs. Chips’ potato chips.
However to make the investigation a fair test I must keep several things the same. These will be:
- I will use the same amount of water in each test tube (30cm3)
- I will use the same size of potato chip in the test tubes (3cmx1cmx1cm)
- I will use the same number and variety of potato chips in each test tube (3 repeats)
- I will leave the potato chips in the test tubes for the same time period
- I will do my experiment in room temperature
- I will use the same balance to measure the weight of the potato chips
Apparatus =
6 test tubes
A beaker
18 equal sticks of potato
Salt
Ruler
Safety blade
Top pan balance
Spatula
Measuring cylinder
Dissecting board
Method =
1. Use a standard kitchen knife to peel the potatoes and cut each one into an even, equal block .
2. Use a scalpel and ruler to cut the potato into chips. There will then be 15 chips.
3. Take a test tube rack and place in 6 test tubes
4. Use a measuring cylinder to measure out different amounts of salt solution and 40cm3 of distilled water and pour it into the test tubes.
5. Weigh every potato chip on an electronic balance and record the weights.
6. Put 3 potato chips into each test tube. 3 chips are used to create an average which gives a better set of results
and more accurate graphs.
7. Whilst waiting set out some paper towels with which will dry the potatoes and draw up a basic table for the results.
8. After several hours drain out the solutions in the sink and place all the chips on the paper towel.
9. Dry each chip with the paper towel and then place each one on the scales so to weigh them.
10. Measure each potato on the scales accurately and then record the weights.
During the experiment we had to keep safety in mind. While cutting the potatoes we had to take extreme care and precision not to harm ourselves and others but also to cut the potatoes accurately and equal.
When we receive the results from the experiment we will have to make up a results table showing all the correct data and we will need to use the following calculation:
% change in mass = change in mass (g) x 100
initial mass (g)
Diagram =
Chips
Test tubes of salt solution
1 2 3 4 5 6
Results =
In the first test tube there contained 0% of salt solution. There was a 5.03% change in mass. This shows that these potato chips gained water by osmosis. In the second test tube there was 1% of salt solution. Here there was a -15.5% change in mass. The mass decreased therefore showing water loss by osmosis.
The third test tube held 3% of salt solution. There was a -28.3% change in mass which shows an even further decrease in mass and more water loss through osmosis. In the fourth test tube there was 4% of salt solution which gave an average of -11.1% change in mass. There was some water loss but we can see that although the concentration was greater, there was less osmosis in the previous solutions.
In the fifth test tube we used 5% of salt solution which made the potato chips lose -18.6% of water through osmosis.
Finally the sixth test tube contained the most amount of salt, 6% of salt solution. The percentage change in mass was -17.5%.
The cells lost water because of the uneven concentration gradients. Mrs. Chips needs a salt solution so that the concentration gradient will be at an equilibrium. Therefore through drawing my results on my graph and producing a line of best fit, I would advise Mrs Chips to use a mixture of salt and water that contained 0.175% of salt solution.
I predicted, before I carried out the experiment, that Mrs Chips should possibly use a solution that would be approximately 0.1-0.2% of salt solution. Therefore my prediction was correct.
The potato chips in the 0% salt solution increased in size because they took in water by osmosis. The cell contained a more concentrated solution to that of the surrounding one, so water molecules move through the cell membrane in to the cell. This makes the cell turgid.
The potato chips in the stronger salt solutions decreased in size because of the loss of water by osmosis. The cell contains a more dilute solution to that of the surrounding solution. This means that water molecules will leave the cell which makes the cell plasmolysed. We wanted to find a concentration gradient at an equilibrium which we found to be 0.175% of salt solution. This is the pint on the graph when the gradient passes over the x axis and there is no change in mass, therefore no osmosis occurs. There is no change in mass, as you can see in the diagram, because there is a horizontal concentration gradient and both concentrations in the cells solution and the surrounding solutions are the same.
The results we recorded were all done accurately. We dried of the potato chips so that there was no excess water to make the mass increase. The results were mostly similar but in the test tube that contained 3% salt solution, one of the potato chips increased in mass although we did expect it to decrease in mass because the cell was more dilute compared to the surrounding solution. All our other results were accurate.
- To ensure we created a fair test we made sure there was
- The same volume of solution in each test tube
- The same size of potato chip in each test tube
- Three potato chips in each test tube
- The same time period used for each investigation
I was very pleased with all y results through the experiment as they were mostly accurate and they created a suitable solution for Mrs Chips to store her chips.
