I required the following apparatus to carry out my preliminary work: 1.00M sucrose, 2 Beakers – to hold sucrose solutions and water, Water, Cork borer (4mm) – cuts out accurate potato chips, Blade of some sort to cut potato chip to size, Ruler to measure length of potato chips – to get the same length potato chips, Scales – weigh the potato chips to 2.d.p for accuracy, Potato, Cutting tile, Syringe to get more accurate measurements and Measuring Cylinders to measure how much water and sucrose I need. Using this apparatus will help me seeing which piece of apparatus is useful and which isn’t so when doing my proper investigation I can deduce what apparatus I require. I set the apparatus as shown in the following diagram:
Once this is done I will follow a similar method to the one which I will carry out when using both carrots and potatoes. The quick method I carried out was:
Make solutions – different concentrations, put solutions into test tubes and label them, make potato chips, make potato chips all the same size, weigh potato chips, put potato chips into solutions for 3 hours or more, re-weigh potato chips. The results I gathered are on a table shown below:
My results showed that my prediction was correct. My results showed that as the concentration of sucrose increased the weight of the potato chip decreased from its normal weight; and as the sucrose concentration decreased the weight of the potato chip increased from its normal weight.
Also by looking at the results table I can see that as the concentration of sucrose solution gets weaker the less water has moved out of the potato chip. This is because water moves into the cell from a high concentrated area to a low concentrated area. Because the potato chip is heavier in the weaker solution it shows that water has moved into the potato chip. This means that in the stronger solutions water moves out of the potato chip because the water potential is lower than in the potato chip so water will diffuse (osmosis) out of the potato chip into the strong sucrose solution. The water potential of the actual potato was 1.4kPa.
As mentioned earlier the reason for carrying out preliminary work was to minimise errors for when I carry out the proper investigation. There were some errors that I encountered during the preliminary work and they were:
Anomalous results, getting correct concentration of sucrose solutions, weighing of the potato chips before putting them into solutions, length of the potato chips. The reason for having anomalous results was because I forgot to weigh the potato chips before they went into the sucrose solution. This was a major error on my account and have to remember to weigh the potato chips and carrots chips for when I carry the proper investigation out. I have to make sure I make the length of both the potato chips and carrot chips the same length so I will have to decrease the length of the potato chips as I made them quite long. I will have to make them small as carrots get thinner as you from top to bottom and you won’t be able bore holes from the top only. I also need to repeat the investigation or use more carrot and potato chips for reliability.
This ‘preliminary’ work will give me guide lines to as what I should do and not do for when I carry out my investigation.
Prediction
I predict that as the concentration of sucrose solution increases there will be a decrease in mass. There will be a gradual decrease in mass from a 0.2M concentration up to the 1M concentration. The mass change from the original mass will differ as some values will increase from the original mass and some values will decrease from the original. This happens because of osmosis. Osmosis is when water molecules move from a high concentrated are to a low concentrated area. So for example in the 0.8M solution the water will move out of the potato chip as there is a lower concentration of water molecules (higher concentration of solute molecules) in the solution than in the potato chip. But however the case will be different in the 0.2M concentration solution. Water will move into the potato chip as there is a lower concentration of water molecules (higher concentration of solute molecules) in the potato chip than the solution. Water moves down a water potential gradient and tries to reach equilibrium, this is where there’s a balance of water molecules on both sides of a partially permeable membrane, in this case inside the potato chip and outside the potato chip.
Apparatus
This is the list of apparatus I will need to carry out the investigation:
- 1.00M sucrose
- 2 Beakers – to hold sucrose solutions and water
- Water
- Cork borer (4mm) – cuts out accurate potato chips and carrot ships
- Blade of some sort to cut potato chip to size
- Ruler to measure length of potato chips – to get the same length potato chips
- Scales – weigh the potato chips to 2.d.p for accuracy
- Potato’s – as many as required to make 18 2cm potato chips
- Carrot’s – as many as required to make 18 2cm carrot chips
- Cutting tile
- Syringe to get more accurate measurements
- Measuring Cylinders to measure how much water and sucrose I need.
- Labels – to put on test tubes so different concentrated solutions can be identified.
Risk Assessment
Safety is always an issue to be aware of so to make sure that accidents keep to a minimum I will try to keep close to where I am working. All coats bags and stools should be put onto the sides because there’s the danger of tripping up. Also on the razor blade I will keep a piece of paper covering the sharp end to stop anybody from getting a cut.
Wearing a lab coat is also a good idea as this will keep your clothes from being stained by the sucrose or getting wet. I don’t think there is a need for safety goggles as there aren’t any harmful chemicals being used thought there is the razor blade which could cut someone’s eye but the chances of that happening is low so I would say it is optional to wear safety goggles. Also when cutting the potato chip I will use a tile to stop any damaging anything.
Method and Diagram
The first step that will be carried out is attaining the apparatus and setting it up as follows:
- Once all the apparatus is set I will then make my solutions out by making different concentrations as shown in the table below:
As you can see there will be 6 different concentrations that will be made.
- I will put these different concentrated solutions into test tubes and put them into a test tube rack. I will also label them so I know which test tube contains which concentration of sucrose.
- I will then get a size 4 cork borer and make 18 2cm potato chips and 18 2cm carrot chips.
- I will then weigh these but wiping them down before hand and recording down the results.
- Once this is done I will put the potato and carrot chips into the test tubes. 6 chips will go in each test tube, 3 potato chips and 3 carrot chips.
- I will then leave these inside the test tubes for around 3 hours or more.
- After this I will take them out of the test tubes, wipe them down so there isn’t any solution left on and then re-weigh the carrot and potato chips and record the results.
Variables
My variables for this investigation are sucrose concentration, potato/carrot chip length, the weight of potato/carrot chips, the amount of water and sucrose in each test tube, size of potato chip and the amount of solution in each test tube.
Things that I will be changing in this investigation:
- The concentration of the sucrose solution.
- Weight of potato/carrot chips – these will be different as the potato/carrot chips won’t all weigh the same.
- The amount of water and sucrose solution in each test tube will be different so different concentrations can be made.
Things I will keep the same in this investigation:
- The length of the potato/carrot chip.
- The size of the potato/carrot chip (use cork borer size 4)
- The amount of solution in each test tube will be 20ml of a mixture of water and sucrose depending on the concentration of the solution.
Results
Table of results to show the weight of potato chips before and after being in different concentrations of sucrose solution and the difference.
Table of results to show the weight of carrot chips before and after being in different concentrations of sucrose solution and also the difference.
Table of results to show the average weight of potato chips before and after being in different concentrations of sucrose solutions and also the difference.
Table of results to show the average weight of potato chips before and after being in different concentrations of sucrose solutions and also the difference.
After getting my results I needed to get the water potential for the carrot and potato using my graph of results and my conversion graph.
Table of results to show Water potential for three carrots and 3 potatoes’
Graph and Table of results conclusion
By looking at my table of results and graph I can see that my prediction was correct. The graphs show as the concentration of sucrose increases the difference decreases. This shows that the mass decreases significantly from the original mass for potato chips and carrot chips which were in higher concentrated solutions of sucrose. This shows that water has moved out of the potato chip as there is a lower amount of water molecules outside of the potato/carrot chips so water moves out to try and reach equilibrium. This also makes the potato/carrot chip become falcid.
As the concentration of sucrose solutions decreases the difference begins to increase. This verifies that less water is moving out off the potato chip and instead water is moving into the potato chip as the mass begins to increase from the original. Water moves down a water potential gradient and because there is less water in the potato/carrot chip water will move into the potato/carrot chip trying to reach equilibrium. This also shows that the potato/carrot chip becomes turgid.
Both the graphs and tables show a general trend. The graph shows that as the concentration increases the mass begins to decreases as water moves out of the potato/carrot chip.
T-Test
The t-test assesses whether the means of two groups are statistically different from each other. This analysis is appropriate whenever you want to compare the means of two groups (definition of T Test from ).
Hypothesis:
- Null – This hypothesis will be accepted if there isn’t really any significant difference between the potatoes’ water potential and the carrots water potential.
- Alternative – This hypothesis will be accepted if there is a difference between the potatoes’ water potential and carrots water potential.
Firstly I have to put the water potentials into a table and also have to square the water potential values with the Σ from each column as shown below:
You can see that the mean has also been put in as this is important for when doing calculations.
Now that the means have been worked out I have to calculate the variance for sample (S) 1 (potato) and 2 (carrot) using the equation:
By substituting in the values you can work out the variances for S ² and S ²:
Once sample ones variance has been worked out we have to work out the variance for sample 2:
Now that I have figured out the variances I can begin to figure out what ‘t’ is by using this formula:
Now that we have a formula for ‘t’ we can begin to substitute the values:
= 0.11
——
0.25
t = 0.44
Now that ‘t’ has been figured out we can by using the table of ‘degrees of freedom’ (sample size) we can see whether there is a null hypothesis or a alternative hypothesis. We can work out the ‘degrees of freedom’ by using this formula:
n + n - 2
= 3 + 3 – 2
= 4
This shows that ‘t’ is smaller than the critical value at p<0.05 (2.776) so we accept the null hypothesis meaning that there isn’t a significant difference between the potato and carrot.
Conclusion
By looking at the overall results with the t-test and ‘degrees of freedom’ data, you can see that potatoes’ and carrots don’t entirely have significant differences in terms of water potential.
There are some differences between the potato and carrot such as potatoes’ are more turgid than carrots as they can hold more water in them. I know this by looking at my results table. Also carrots tend to lose water a lot easier than potatoes’. Overall they seem pretty similar because by looking at the results table you can see that the concentrations between 1M and 0M the values are around the same.
Evaluation
During my experiment I tried to minimise errors as much as I could and by doing preliminary work I cut down on errors even more. Unfortunately errors still occurred during the investigation, some due to apparatus and some human errors.
The errors that occurred were not having enough test tubes, measuring potato/carrot chips length. Errors that could have occurred without me knowing were probably when doing most of the measuring such as measuring solutions and also possibly when weighing the potato/carrot chips. Any of these errors could be due to a misreading or human error. The effect of most of these errors would or could have resulted in unreliable results and these are significant in that you wouldn’t have to make much of an error to get unreliable results and results which don’t fit a pattern.
To most problems there’s usually a solution and I these are the steps I will take in minimising more errors if I were to repeat this investigation again:
- Apparatus (supply) – make sure that there’s enough of something that is needed as I had only the use of six test tubes for putting solutions and 36 carrot/potato chips in. Also to use more accurate apparatus such as a bulb pipette and burette to get solutions that are more liable to be closer to the value that you want the concentration to be (such as 0.2M).
- Apparatus (measuring length) – using a micrometer to measure the length of the potato/carrot chips and cut them to size, it is more reliable than a ruler (which I ended up using)
- Repeat test – This would increase the reliability of my investigation, even thought I retrieved an adequate amount of results for my investigation, the more test you do the better the reliability.
To finish off I think that the investigation was a success but with room for improvement, mainly to do with apparatus.