Figure 1: Showing Osmosis
My theory in this experiment is that, due to the difference in the water concentrations of the two substances, I believe that the weight of the potato will start decreasing when it is tested on 0.2 molar solutions of glucose and greater.
Equipment:
- Cork borer number 5
- Six test tubes
- Measuring cylinder
- Two decimal place balance
- Potato
- Scalpel
- Glucose
-
Distilled water
Apparatus Diagram:
Method:
I plan to carry out this experiment by using all the safety issues and fair testing procedures to give me the most reliable and most accurate set of results.
I plan to have use glucose as the sugar solution prepared with concentrations from 0.1M to 1.0M, in intervals of 0.2. Then sections of potato will be cut using a cork borer number 5 and knife to equal lengths (5cm) keeping the surface area constant. I will then measure each tissue of potato using a measuring scale, measured in grams, when I do this I will place the potato on the scale and resetting the scale so that I only get the weight of the potato. I will then add 20ml of each concentration of sugar in two test tubes, giving me a total of 6 test tubes, and labelling each molar reading. Then to each test tube a cut piece of potato will be added and its concentration added to the label. These will be left for 30 minutes. Then the potato pieces will be removed from the test tubes, and surface solution on the potato will be removed using paper towels. I will then measure the potatoes again, recording its change in mass by weighing them. I will then be taking the two readings of each molar concentration. This is because I will be doing a repetition of the experiment, as it will save me valuable time. These results will be taken for each concentration in order to get an average and reduce the effect of anomalous resulting.
As it is difficult to get the cut potato pieces to the same mass it was decided that I would use a percentage change in mass that will be used to compare the data in the results, as this would be far more accurate. I will do this by taking the difference in mass; divide it by the mass before of he potato and multiplying it by 100.
Fair Testing:
In this experiment on osmosis there should only be two changing variables:
1: Different moralities of sugar solution,
2: Change in mass of the potato samples.
To keep these two variables the only variables in the experiment I must:
1: Keep the potato samples the same length (5cm). This is because if one potato sample is 1cm long and one is 3cm long then the 3cm long sample will have a larger surface area and will osmosis much more quickly.
2: Use the same potato. This is because many factors due to the potato may affect the experiment. For example the age and sizes might be different, which means one potato might have more water in them then another.
3: Stop the evaporation of any of the molar solution. This is because if the sugar solution evaporates past the level of the potato, then the potato sample will have less surface area in the solution so this would make osmosis happen much slower. To stop any solution evaporating a cork lid can be placed on top of the test tube.
4: Accurate amount of sugar solution: More Bathing solution may affect the rate of solution. To make the amount of solution placed in the test tube as accurate as possible a syringe will be used to measure out the exact amount needed.
5: Contamination: As each test tube is filled up with the different molar solutions the syringe which would measure the amount of solution placed in the test tube may become contaminated with different moralities. To stop his from happening, the beaker and syringe must be washed every time they are used.
6: Average: To make the experiment as accurate as possible an average will be taken out of the 6 sets of results taken. Also any clearly anomalous results will be ignored.
Results:
Analysis:
The evidence obtained from this investigation supports the prediction I made. It also shows that the potato cells increase mass in solutions with a high water concentration and decrease in mass in solutions with a low water concentration.
In this experiment, I believe that I have collected enough data to support my hypothesis. This investigation was, I think, successful. Successful meaning my results collaborated my predictions.
The potato cells, working to stay alive, took in, or gave out the water depending on the concentration of the tissue and the concentration of the solution it is surrounded in.
The results were fine and by looking at the weights measured before the experiment, you can see that there is no reading, which seems to be out of the line. As the weights before the experiment range between 1g and 1.86g, this tells us that the potato pieces were cut well, and I believe accurate enough. There were, I believe, no anomalous results after the experiment, as the weights were very similar in there own category. This tells us that my experiment was successful.
The graphs and the results show that:
· Osmosis actually took place in the experiment.
· As the molars increased, the percentage of the weight difference decreased.
There doesn't seem to be any results, which undermine my predictions, and I didn't find any anomalous results, which means I didn't have to repeat any of our experiments more than twice times.
Having the results, which backs up my hypothesis, proves that this investigation was fully accomplished, and was an achievement.
In the table seen on the last page, the percentage shows a steady decrease, telling us that the percentage of the difference decreases as the water concentration decreases.
This experiment helped me find out that osmosis occurs between 2 liquid substances with a partially impermeable membrane, and that higher the water concentration is the larger increase in grams (mass). This means that the percentage will also be higher, increasing with the grams.
Evaluation:
I believe I gained accurate and sufficient enough results, shown on my graph and tables that concludes the experiment, and to prove my hypothesis. My final results were very reliable, due to the precautions I took to make this a fair test.
Looking at the overall experiment I have thought of a number of improvements to give me more and better accurate results. Firstly the concentrations were measured using a measuring cylinder and could be made more accurate using titration. Also when the potato was dried to remove surface liquid it was not necessarily done the same on each potato, a more accurate and uniform way of drying would improve the accuracy further.
Using more types of molar glucose solutions would have helped me obtain better results, and more accurate results, so that I can make sure the results are totally correct.
Experimenting with one set for a longer period of time, for each set, would lead us to better results, because the osmosis action would reach its maximum capability, and therefore tells us how much water could be transferred for each solution.
Further work could be carried out to include concentrations that increased in 0.05 M rather than 0.1. This would increase the accuracy and improve the graph. Other investigations could include using different varieties of potato or different plant tissues e.g. carrot, apple.
I could also extend this experiment by repeating it exactly as before. However this time I could take more results at the molarity levels 0.20, 0.21, 0.22,0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30. This would produce much more accurate results.
Other variables in the experiment could be changed for example instead of changing the mass of the potato the species of the potato could be changed. For example I could use a new potato and a really old potato.
Also the shape and size could be changed. However this would not affect the results much. This is because the variable would only change the rate of osmosis because of a different weight and size.
Temperature could also be changed for example the samples could be placed in different water baths and brought up to different temperatures to see if temperature played its part in the osmosis of potatoes. 5 sets of 5 potatoes could be placed in water baths at 10oC, 20oC, 30oC, 50oC and 60oC. Then leave them for 24 hours making sure all the variables in the first experiment still apply however just using one molar solution. Then after 24 hours re-weigh the samples and record the result. I would expect that at high temperatures the potato samples would osmosis the most. This is because at high temperatures the solutions water molecules would move faster and therefore equal the concentration faster. A preliminary experiment could be set up beforehand to find out how long the experiment should be kept going because if the concentration of the potatoes equalises then the weight of the potatoes will be almost exactly the same.
But overall, given the apparatus that I got to carry out the test, I think this experiment turned out to be very successful, and I'm very please with my results.
