Scientific reason for my prediction
In nature water concentrations will always try and balance by osmosis. This is how a plants roots absorb water from the soil. The root cells have a higher concentration than the damp soil, so the water is drawn in.
In my experiment the potato has a low water concentration and therefore it will draw water out of the weaker sugar solutions. It will also lose water to the stronger sugar solutions. The movement of water to or from the potato will stop when the water concentrations have equalised.
Plan
1. I plan to collect my equipment which include:
A potato
A cork borer
A pair of scales
A scalpel
1 molar sugar solution
5 beakers
A 20ml-measuring cylinder
Water
2. I will look at my results of the pre-test and figure out what concentrations of sugar solution I will need. I decided I would do 0.10molar, 0.20molar, 0.30molar, 0.40 molar and 0.50molar so I would get lots of different results.
3. I will then prepare my equipment by firstly getting the 20ml-measuring cylinder and measuring the concentration of the sugar solution.
I will do this by getting 10mls of sugar solution and 10mls of water for the 0.50molars.
For the 0.40molars I will need 8mls of sugar solution and 12mls of water.
For the 0.30molars I will need 6mls of sugar solution and 14mls of water.
For the 0.20molars I will need 4mls of sugar solution and 16mls of water
For the 0.10molars I will need 2mls of sugar solution and 18mls of water.
I will then put my five different concentrations in to the five beakers.
4. Next I will cut a length of potato with a cork borer and cut three slices, each at 1cm long for each beaker. All together I will cut 15, 1cm potato slices with a scalpel. I will dry the potato slices so the excess water is removed which may cause anomalous results.
5. I will then weigh them on the scales and record the weight of each piece. I will get each piece the same weight so I don’t need to worry, about which piece of potato is which (if necessary by trimming them).
6. I will place three pieces of potato into each of the five beakers and I will then leave them overnight and return to them the next day.
7. I will weigh the potato pieces the next day on the scales and record the results.
Safety precautions
I will need to take safety precautions when using a scalpel because it is very sharp. Luckily it will be the only safety precaution we will need to take because it is a safe and easy task.
Fair test
· To make sure that this test is fair I must ensure that all the potato pieces are as identical as possible. Firstly I cut each piece so that they are all the same size (1cm long).
· I then dried all the pieces so that they would all start with the same water content.
· I then weighed all the pieces to make sure that they all weighed the same. Any pieces that weighed too much were carefully trimmed until they were the right weight (0.30grams).
· The sugar solutions were all measured to be the same amount (20ml).
· The five experiments were all conducted at the same time, for the same length of time.
· This also ensured that the experiments were all carried out at the same temperature.
Investigation
I collected my equipment, which included:
· A potato
· A cork borer
· A pair of scales
· A scalpel
· 1 molar sugar solution
· A beaker
· A 20ml-measuring cylinder
· Water
I then prepared my equipment by setting up the concentrations of the sugar solution with a 20ml-measuring cylinder.
Firstly I got 10mls of sugar solution and 10mls of water for the 0.50molars. For the 0.40molars I needed 8mls of sugar solution and 12mls of water. For the 0.30molars I needed 6mls of sugar solution and 14mls of water. For the 0.20molars I needed 4mls of sugar solution and 16mls of water. For the 0.10molars I needed 2mls of sugar solution and 18mls of water.
I then put my five different concentrations in separate beakers.
I cut a length of potato with a cork borer and then cut it into three slices each at 1cm long. I repeated this five times so that I had fifteen pieces. I weighed each piece and they all weighed 0.30 grams.
One thing that didn’t make it a fair test was that they didn’t all weigh exactly the same and the sugar concentration would have been slightly different.
I dried the potato slices to make them get rid of any excess water. I then placed three slices of potato in each beaker and left them for one night.
The next day I checked them and weighed them again. This time I got more accurate results.
Results
Concentration Weight at start (gm) Weight at end (gm) Average (loss/gained gm) Difference
0.10molars 0.30 0.39 0.38 +0.08
0.37
0.39
0.20molars 0.30 0.32 0.33 +0.03
0.33
0.34
0.30molars 0.30 0.27 0.27 -0.03
0.26
0.28
0.40molars 0.30 0.27 0.26 -0.04
0.22*
0.28
0.50molars 0.30 0.25 0.25 -0.05
0.25
0.25
I only had one anomalous result (*). This was when I did the 40molars. I would have either got this result because I didn’t cut this slice to weigh exactly 0.30grams or I didn’t dry the potato slice as much as the other slices. I could have made it more accurate by putting a mark on each piece so I would know which was which. I could also have weighed it to three decimal places to be more accurate.
Conclusion
My prediction was correct because at 0.10molars it increased weight the most and at 0.50molars it decreased the most. I drew a graph showing how much weight was lost from the potato slices. The graph shows that the concentration of the sap inside potato cells is 0.295 molars because this is where my line of best fit crosses the axis, which is where the potato stays the same weight all the way through the experiment. So it hasn’t lost or gained any water so the concentration of the sugar solution is the same as the concentration of the sap inside the potato cells.
It changed weight when we did the other concentrations because the sugar solution blocks the pores and only lets the water through one way. Depending on the concentration the higher it is the more sugar particles are blocking holes on the outside of the cell and the more water can come out so it will lose weight. The water only goes through one way because the water on the inside of the cell push it out of the way where as the water on the outside can’t push the particle into the cell and out of the way so a lot less water comes in than out. On the second diagram there are less sugar particles and there is more water particles in the sugar solution less pores are blocked so the water enters the potato cell via the pores.
Scientific reason for what I found out
The lower the concentration of the sugar solution the more water the potato cells are going to gain and therefore the more they will weigh. So the higher the concentration of the sugar solution the less water the potato is going to gain and therefore the less weight it will gain. The highest concentrations of the sugar solutions will cause the potato to lose water and therefore to lose weight. Water movement of this type is called osmosis. Osmosis is the movement of water molecules from a high concentration of water molecules to a low concentration of water molecules through a semi-permeable membrane.
Evaluation of investigation
My results concur with my prediction therefore I think that the conclusion is a valid one. By using three pieces of potato the result of each experiment is checked three times for greater Reliability.
I only had one anomalous result in my experiment, this was one of the pieces of potato in the 40molars solution. I presume this result was because it was not the same weight and size as the other two pieces. I think the result of this anomaly can be rejected because of the small amount of pieces of potato used. This result would drag the average down to far. If more pieces of potato had been used (say 10) then the result could be included because it would not affect the overall result in any significant way.
The results of my experiment are reliable because the line of best fit almost goes through all my results on my graph. The results all seem to give the right answer if you ignore the anomalous result. Strong sugar solutions draw the water out of the potato and weak solutions lose their water to it.
To be on the safe side I think that the experiment should be repeated using more than the five sugar solutions that I used. The next experiment should also include sugar solutions outside and inside the scale that I used. This would include 0.0, 0.05, 0.15, 0.25, 0.35, 0.45, 0.55 and 0.6 molars as well as the strengths that I used in the first experiment. To get a greater accuracy in the next experiment, I think that more than three pieces of potato should be used in each beaker. I think that ten pieces of potato should be used in a larger beaker with a larger quantity of sugar solution. This should ensure that any anomalous results would not affect the average result to a great degree.
To make my investigation more accurate I measured my solutions in a 20ml-measuring cylinder with my head level with it so I could get a clearer reading and I would get the right amount I wanted.