- Clean beakers x 6
- Sharp scalpel and tile.
- Potato x 1
- Cork borer (size 4)
- Scales
- Sucrose x 150g ( 1g = 1% of sucrose solution)
I have decided that there will be 6 different concentrations of sucrose. The first beaker will contain only pure water, and then add 10g of sucrose to the previous amount into the next beaker. Every beaker will be filled with 100ml of pure water. When creating the solution to keep it a fair test I will put the sucrose into the beakers and then fill it to 100ml, this is to keep each solutions volume the same. I have also decided not to stir the solution.
When I measure the level inside of the beaker will measure it from the meniscus level. This is where the water level rises as tension increases near the glass. I will then extract 18 cylinders of potato, from the same potato because the potatoes may have different concentrations. All of the 18 cylinders will have equal diameters – cork borer size 4. All the experiments will be conducted over a dinite period of 24 hours.
In each beaker there will be 3 cylinders of potato. This is so that I can take an average for each concentration. I have chosen to record the results of a beaker with just pure water, so that I can make comparisons with concentrated and un-concentrated solutions. Below is an example of how I will record my results;
Although this is a fairly safe experiment I have to be aware of the potential dangers. When using the scalpel I will have to be very cautious of the blade, as it is easy to slip and cut your self. I will make sure that I know where the blade is at all times and return it to the place where I got it from.
Incase of test tube breakages, I will notify the teacher straight away, and get it cleared up before any thing else happens. I will avoid handling the broken glass.
I will also wear safety glasses to avoid anything coming in contact with my eyes.
I shall make sure that the surface and the space around me is dry and tidy before I carry out the experiment, as the water may affect the results and it will be easier to locate things when I need them. I will also check the floor if it is wet, to avoid any one slipping up whilst rushing about to get equipment (even though they should not be).
From a similar experiment I have done previously I have learnt that just taking measurements of the potato cylinders is not accurate as the potato expands both lengthways and out wards during this process. Hence why this time I will be recording the mass, as opposed to the length. I will record the weight before and after the experiment to compare the increase or loss of mass. This will be more accurate.
Also from similar experiments I have gained knowledge of different variables that affect experiments, and so the following will be taken into account;
Solution volume – remember to fill beakers after sucrose is added.
Duration of experiment – each experiment will start a few minutes behind the
previous one because of preparation time.
Temperature – surroundings in the experiment will affect the rate.
Weighing scales – could have un-noticed errors.
My hypothesis for this particular investigation is that the lower the concentration of the sugar solution in the beaker the larger the mass of the potato. This is because the water molecules pass from a high concentration - in the water itself, to a low concentration - in the potato cylinder. Therefore, the cylinders in higher water concentrations will have a larger mass than in higher sugar concentrations.
RESULTS;
I carried out the experiment with no difficulty and followed my plan exactly. I only took one extra precaution just to be more accurate, which was to weigh the sucrose in the beaker on the scales (set to zero) because I firstly transferred the sucrose to the beakers after weighing it and some started to fall out as I poured it in.
From these results I can see that the more water in the solution, in ratio to the sugar, the more weight is put on by the potato. This is caused by osmosis. I can also deduce the point where no transaction is made – in the 20% sucrose solution, trial 2 (highlighted in green). This was not an anomalous result as it still fitted in with a pattern. The experiment backed up my prediction that the pure water solution would gain the largest mass – 0.4g, and the highest concentration would gain the least. But, I did realize that the cylinders shrink in size by as much as 0.6g.
The cutting of the potatoes was the most difficult part of the experiment as although I was recording my results by mass, it could well have affected the surface area and so the overall rate of osmosis. This is probably the only outside influence on the results I can see.
Graph on the next page. P.T.O.
The experiment was very successful in my opinion. I obtained a large quantity of very accurate results from which I was able to create informative graphs and I was able to make a solid conclusion. I think I took easily enough results for the amount of concentrations that I was using, and the time that I used for the experiment to last was enough to allow sufficient osmosis to occur. The consistency in the results suggests that the apparatus I selected and used in this experiment was appropriate.
However if I was to repeat the experiment I would increase the time of the experiment to allow more osmosis to happen and possibly find out the saturation point of the potato tissue. The range of concentrations I chose, I believe to be adequate, but I would possibly create more concentrations, if I repeated the experiment, so that I would have more varied results, i.e. 5%, 15%, 25%, and so on. Also, I would try not to loose any water through evaporation or let any unwanted substances into the solution with the potato, next time, and so I would cover the opening of the beaker.
There were not any out of the ordinary results, but some were not as close to the line as others. This may have been caused by human error. When the potato cylinders were removed from the beakers and dried I may well have dried some potatoes more thoroughly than others and so some would have more excess water, which would add to the mass. If the experiment was repeated and I could find another way to dry the potatoes that would ensure that all were dried in the same way for the same time, I would. However with all this said I think that the experiment was truly successful and I was very pleased with the complete comparison of my results with my initial prediction.
