Concentration of Sucrose Pure Water Sucrose 80% Change
A B A B A B
0% 0.900 0.710 0.960 0.800 +0.060 +0.090
0.1% 0.870 0.880 0.970 0.960 +0.100 +0.120
1% 0.900 0.870 1.040 0.950 +0.140 +0.080
10% 0.610 0.800 0.500 0.760 -0.110 -0.040
80% 0.750 0.790 0.420 0.560 -0.530 -0.230
Conclusion
Potatoes in & to 1& sucrose solution increase in mass. This shows that there is at least 1% of sucrose in the potato.
Potatoes in 10-80% sucrose solution decrease in mass. This shows there is no more then 10% sucrose in the potato
To find the exact percent of sucrose in a potato I will use 2%, 4%, 6%, 8%, 10%.
Osmosis Coursework
Aim: To Find The Exact Concentration Of Sucrose Inside A Potato
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
In a high concentration of water the amount of sucrose is low. This is a weak.
In a low concentration of water the amount of sucrose is high. This is a strong 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. This means that if there is less water in the potato then solution around the potato, water will travel into the potato so it can join with the sucrose to make a strong bond. As there is less water in the potato there is more sugar for the water in the boiling-tube to bond with. When there is the same amount of sucrose in the potato and solution no change in mass will occur as there is nowhere for the water to travel
Sucrose cannot travel through osmosis, as it is too large. In this case only water can travel through the semi-permeable membrane (potato skin).
Prediction: From My Preliminary Work I Have Found Out A Potato will ALWAYS increase in mass when placed in pure water, as there is less water in the potato then the solution so water from the solution will enter the potato. I know this because like my introduction states, the water will travel into the potato to try and join with the sucrose solution. Through my preliminary work I also found out that the sucrose concentration inside a potato was between 0% and 10%. Using that knowledge I predict that the potato in the lower amounts of solution will increase in mass and decrease in mass when the amount of sucrose is higher.
Apparatus: 10 boiling tubes, 2 boiling tube racks, bottles of sucrose solution (2%, 4%, 6%, 8%, 10%) 1 large potato, or two of the same height, stop clock, potato borer.
Fair Test:
To keep it a fair test, all the boiling tubes are in the same temperature water so it does not affect the experiment, there will always be the same amount of sucrose concentration in each boiling tube so that that does not affect the experiment either. Those two variables would speed up the rate of reaction making it unfair. All potato cylinders will be from the same potato so the same amount of sucrose will be in each one.
Method:
- Set 10 boiling tubes in a rack
- Put 10cm3 of the sucrose concentration in each boiling tube. Use:
2% twice
4% twice
6% twice
8% twice
10% twice
- Bore 10 cylinders from the potato, must be the same size (2 per concentration)
- Weigh each cylinder and record in results table
- Place a cylinder in each tube
- Start time straight away
- After 40 mins remove each cylinder and blot.
- Weigh each cylinder and record in results table.
- Record changes in mass
Results
Concentration of Sucrose Mass At Start Mass At End Change Average
A B A B A B
0% 0.900 0.710 0.930 0.780 +0.030 +0.070 +0.050
2% 1.240 1.160 1.250 1.150 +0.100 -0.1 0
4% 1.320 1.190 1.320 1.190 0 0 0
6% 1.180 1.220 1.180 1.180 0 -0.400 -0.2
8% 1.320 1.320 1.290 1.250 -0.030 -0.070 -0.5
10% 1.170 1.320 1.120 1.210 -0.050 -1.100 -0.8
Conclusion
From my investigation I have found out that there is approximately 4% sucrose. I found this out from my graph. The line of best fit runs through the point of no change at about the 4% mark. Also on one of my results, there was no change in the mass of the potato at 4% solution. This ties in with my prediction that the amount of sucrose in a potato will be between 0 and 10% sucrose solution. Also the potato as predicted, increased in mass in the lower sucrose solution, as there was more water in the solution then the potato, so as my introduction says, water would leave the solution to enter the potato and join with the sucrose. When there was a higher amount of sucrose, as I predicted the mass of the potato decreased because there was more sucrose in the solution then potato, so the water left the potato to join the solution.
My experiment proved my introduction and prediction fully. It proved that if the concentration of sucrose were higher outside of the potato then the water from inside the potato would leave the potato to join it. Therefore the potato will lose mass. If the solution of sucrose around the potato is less then inside the potato, the water in the solution will enter the potato to join with the sucrose as that is what water molecules are always trying to do – find a partner. Therefore the potato will increase in mass. If the amount of sucrose is the same inside and outside the potato, the mass of the potato will not change. As there was no change in mass in 4% solution, the percentage of sucrose in the potato was 4%.
Evaluation
Whilst carrying out this investigation, I found that it was difficult to measure a significant difference in mass. There were many variables that affected it, the amount of sucrose solution added, the temperature, if the potato was blotted and weighed correctly. I believe throughout our experiment we made sure it was fair. Perhaps a better method would have been to leave the potatoes overnight, to give the water to travel in and out of the potato until the osmosis process has finished. Our results were very accurate; there was only one anomalous point in the graph, which was the 2% concentration point. Though the line of best fit was very accurate and showed where the point should have been. The point could have been wrong, for a number of reasons; maybe we did not blot the potato enough or did not weigh it properly. To improve my experiment I would have left the potatoes overnight to give them time to fully osomosise, also completely check the weight of each potato was right and it was fully blotted before weighing. This would have maybe given more acute results.
I think my results are defiantly accurate enough to support my conclusion. Almost every value fits or is very near the line of best fit on my graph. And my prediction and introduction were proved by the conclusion and results. If I were to extend the experiment I would have used the sucrose concentrations, 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, this would have given much more accurate results, and I would have used 3 potato cylinders for each solution to make it absolutely fair. I would have got a much clearer idea of what percent sucrose solution is in a potato and even if one potato cylinder or two was a bit wrong the other two would have evened out the results.
By Leo Matlock
