20% sucrose solution
Scales
Borer
5 test tubes
Syringe (maximum measurement of 10ml in 1ml increments)
Potato
Test-tube rack
Labels
White tile
Knife
Diagram
Method
5 strips of potato will be made using the borer on the white tile. They will then be cut to roughly the same size using the knife making it easier to fit into the test-tube. The five pieces will then be weighed on the scales and the weights recorded. Each piece of potato will be placed into different test tubes, labelled A-E. 5ml of the 20% sucrose solution will be added to each test-tube using the syringe. A will then b left in the 10°C water bath, B in the 20°C water bath and so on up to 50°C. all of the test-tubes will be left for 20 minutes in the water baths. After that, the potatoes will be re-weighed and the weights recorded. The experiment will be repeated twice more and the results compared to get an average and to eliminate abnormalities. Abnormalities may occur if the experiment is inaccurate in some way. It could be and inaccurate measure of sucrose solution or an inaccurate weight taken.
Fair Testing
- The same amount of sucrose solution will be used and of the same strength (20%). If it’s not kept the same, the results would not be as expected as the strength and amount affect the rate of osmosis. If it were to change it would be another variable change and in this experiment only 1 variable is to change, which is the temperature.
- They will be left for the same amount of time (20minutes) again because it would be changing another variable.
- Results will be rounded to 1 decimal place.
- The experiment will be carried out a total of 3 times to compare the results and get an average and to eliminate abnormalities due to inaccuracy.
Safety Precautions
- Goggles will be worn to protect eyes from harmful substances used.
- All clothing will be protected by overalls or lab coats.
- Jewellery will be removed to prevent it from getting in the way.
- Hair will be tied back.
Results
Preliminary results
Preliminary results are taken to get useful results. Useful results are results that match the prediction. In this case the results above do match my prediction and as the temperature increased mass was lost. The experiment will be repeated twice more and the results displayed below.
1st set of results
2nd set of results
Overall results averaged
Analysis
From this experiment I have found that as the temperature is increased the more mass is lost. So as the temperature increases the rate of osmosis increases. The particles gain kinetic energy through the temperature. The higher the temperature the more kinetic energy gained.
The graph shows an overall negative correlation. Temperatures 10°C and 20°C have the same change in mass, as do temperatures 40°C and 50°C.
The potato was surrounded by a higher concentrate in sugar therefore the water diffused from the potato to the high sugar concentrate as I predicted. The water does this to equalize the concentrate. The water is able to do this because the sugar particles won’t diffuse, as they are too big. As the particles gained kinetic energy, they moved quicker and diffused through the potato. The more the potato was heated the more kinetic energy it gained therefore the particles moved and diffused quickly.
I expected the lower the temperature to have the lowest change in mass and the higher temperature to have the bigger change in mass. This happened but was not continuous for the temperatures inbetween, as two others had equal results to the lowest and highest temperature.
Evaluation
The results were fairly accurate and there is a general trend though there are two abnormalities. Temperatures 10°C and 20°C have the same change in mass, as do temperatures 40°C and 50°C. I would have expected at 10°C a much smaller amount of change in mass, barely anything because the temperature is so low. I rounded the figures to one decimal place so this could be why it is the same as 20°C. At 40°C I also would have expected a much lesser change in mass. If it were to follow the trend it would have been around –0.25 and then rounded to -0.3 which is why I got an inaccurate result. To make it more accurate I should have rounded all of the figures in all four tables to two or three decimal places. Inaccurate results were obtained perhaps because the temperature on the water bath was wrong, which could explain the inaccuracy of test tube A’s results. If the water bath’s temperature was slightly higher that 10°C slightly more mass would have been lost causing it to be rounded up instead of down.
The method is fairly easy and obtaining the results is also easy. Rounding proved a problem because I only rounded it to one decimal place causing inaccurate results. If I were to do it again I would make sure the water bath is at the right temperature and measure it with a thermometer. I would also round to three decimal places. To be more accurate when weighing I would make sure the scales are completely dry and the potato is as dry as possible.
Enough results were taken to make a conclusion and for each experiment the results matched my prediction. The results would have been even clearer if I’d have rounded to two or three decimal places.
To extend the experiment a wider range of temperatures could have been used. For instance 0°C-60°C. 0°C is the freezing point so it would be interesting to see if osmosis does occur at freezing point. At 60°C I stated that the outside of the potato would disintegrate leaving no semi-permeable membrane. Using 60°C would prove this. If you were to use the capillary tube method it would measure the loss of water not the mass. I chose not to do this method however because it was quite difficult and needed more than one person to tie the visking tube to the capillary tube.
