Preliminary Experiment
This is a practice experiment that I will conduct. This works as a way of finding out what we need to do to improve this experiment and make it a fair test. We used a concentration of 0.50 molars for this experiment.
Equipment List
I will need to use a:
- Scalpel ~ for cutting the potato strips
- Corer ~ to core the potato strips
- Potato ~ to conduct the experiment on
- Tile ~ to cut the potato strips on
- 25ml measuring cylinder ~ to measure how much water or sucrose is present
- Beaker (cup) ~ to put the potato strips inside
- Digital balance ~ to weigh the weight of the potato strips
- Label ~ to label the cup with
- Ruler (ascending in millimetres) ~ to measure the length of the potato strips
- Rubber band ~ to hold the plastic on top of the lid over the cup
- Plastic cover ~ to cover the cup and keep the moisture in
- Sucrose ~ to mix with the water
- Water ~ to mix with the sucrose
- Paper Towels ~ to dry off the potato strips
Method
Before I will start the experiment I will draw out a results table to record my results. I will collect all my apparatus that I need to conduct the experiment. I will measure out 20ml of Sucrose and pour it into a beaker. I will then measure the 20ml of water and I will pour that into the beaker also. I will do this to make a concentration of 0.50 molars. I will get the tile, potato, corer and scalpel. I will place the potato on the tile and I will push the corer through twice to get 2 potato cores. I will then put the 2 cores on the tile and measure them with the ruler to 2cm and cut them. I will try to cut them equally as accurately as possible. I will then write the length down in my results table and I take the potato strips to the digital balance to weigh the potato strips. I will record their results and place the 2 potato strips inside the beaker with the sucrose and water in it. I will get my plastic cup and my elastic band and put the plastic cover over the cup. I will do this so the water does not evaporate because this would change the result. To hold the plastic cover in place I will use an elastic band so the lid does not come off. I will then put the beaker somewhere safe and I will leave it on the side overnight so Osmosis can occur.
The next day I will remove the plastic cover and elastic band. I will then remove the potato strips from the solution and I will wipe the dampness off of the potato strips with the paper towels. I will then take the potato strips back to the digital balance and weigh their weights after the experiment. I will then record their results. I will then work out the average weight before the experiment (potato strip 1 + potato strip 2 divided by 2), after the experiment (same calculation) and change in mass (average weight after experiment – average weight before experiment 100).
Results
After I will do this experiment I will go on to doing my Main Experiment.
Main Experiment
Equipment List
I will need to use a:
- Scalpel ~ for cutting the potato strips
- Corer ~ to core the potato strips
- Potato ~ to conduct the experiment on
- Tile ~ to cut the potato strips on
- 25ml measuring cylinder ~ to measure how much water or sucrose is present
- Beaker (cup) ~ to put the potato strips inside
- Digital balance ~ to weigh the weight of the potato strips
- Label ~ to label the cup with
- Ruler (ascending in millimetres) ~ to measure the length of the potato strips
- Rubber band ~ to hold the plastic on top of the lid over the cup
- Plastic cover ~ to cover the cup and keep the moisture in
- Sucrose ~ to mix with the water
- Water ~ to mix with the sucrose
- Paper towels ~ to dry off the potato strips
- Permanent pen ~ to mark the potato strips
Main Experiment
Firstly I will draw my results table and get all of my equipment. I will write my labels up which will have my name, a letter from A-D and what concentration it is from 0-1. I will measure out the right amount of water and sucrose and I will put it in cup. Each cup has a certain concentration in it so I will put the right amount of solution in each cup.
I will core the potato until I have 15 potato strips. I will then cut them each to 2cm using the scalpel and the ruler. I will then divide the 15 potatoes into 5 groups of 3 potatoes. I will then get a permanent marker and I will mark each potato in each group either with 1 dot, 2dots or 3 dots. So I will have 5 potato strips with 1 dot, 5 with 2 dots and 5 with 3 dots. I will do this so I know which potato is which when it comes to me recording the final results. I will then weigh each potato strip on the digital balance and record the result before I will put it into a beaker. I will put it into a beaker and cover the beaker and I will cover the beaker with the plastic cover. This will stop the water from evaporating and making the test unfair. I will then find out the average mass of the 3 potato strips (potato strip 1 + potato strip 2 + potato strip 3 divided by 3) in each group and put the cups to the side to leave overnight.
The next day I will take the potatoes out and I will dry the moisture off of the outside of the potato strip. I will then weigh them individually on the digital balance and record the results. I will find the average mass after the experiment (potato strip 1 + potato strip 2 + potato strip 3 divided by 3), and use that to find the average mass change overall through the experiment (average mass after the experiment – average mass before the experiment 100).
The factor I will change during the experiment is the concentration of Sucrose. It starts at 0.0 molars and finishes at 1.0 molar. The cups will go up by 2.5 molars so they will be labelled 0.00, 0.25, 0.50, 0.75 and 1.00.
Analysis
On looking at my graph I came to the conclusion that the general trend is when the sucrose content is higher than 0.5 more osmosis occurs. So when there is a high sucrose content the potato strip loses mass. However when the sucrose content is lower than 0.5 osmosis occurs again but the potato strip gains mass in this instance. By doing this experiment I realised that osmosis occurs. As I predicted when the concentration of sucrose in the cup was lower than 0.5 then the mass of potato increased but when the concentration of sucrose in the cup was higher than 0.5 then the mass of potato decreased. This was because the water molecules passed through the visking tubing, to balance out the concentration in the potato strip with the concentration of sucrose in the water. This happened because if the water had a high sucrose content than the potato strip, the potato would allow water molecules in, to make the sucrose concentration in the potato and around the potato even. In the opposite way when the water had a low sucrose content than the potato strip, the potato would allow water molecules out to make the sucrose concentration in the potato and around the potato even. Also my predictions on which way the weight of the potato would increase/decrease to were correct.
Evaluation
I was not completely satisfied with my results and I thought that I could improve my experiment. I came to the conclusion that I could have made the tests more accurate if I had used a syringe for measuring the ml of sucrose and water. I could also have tried to look for a more accurate way of cutting my potato strips because although I had tried my hardest I had not cut all of them accurately. Also I need to put my beakers in a more controlled environment because having them on the side may not have been the best place to put them. I could also have conducted the experiment more than once and then done the averages of them and my results would have been much more accurate. Also not all the potatoes were taken out of the beakers at the same time because I took them out and dried them so some were left in the mixtures longer than others. I could have made this better by putting the potatoes in at 5-minute intervals. For example I could have put the potatoes in cup A at 12:20 and cup B at 12:25 etc. Although with my experiments I was happy with myself because I believe my results were quite accurate. I took every measurement to 2 decimal places and throughout the experiment I used the same type of potato. Another factor of my experiment that I would change if I were to do it again would be how I dried the potatoes. This is because I may have dried some potatoes more than other potatoes. I f I could change this I would put the potatoes on a tissue and place a fan 10cm away. I would then turn the fan on for 30 seconds to dry it before weighing the potato strip.
With all these changes I believe I could improve my experiment and make the results more accurate. However I think that for my first attempt at doing this experiment my results have come out quite accurately.
