To keep the amount of milk and lipase constant I will use a syringe correct to 0.5cm. I will only use the milk and lipase provided for me.
To keep the temperature constant I will use a water bath.
I believe that increasing the percentage of bile will decrease the time taken for the fat to be broken down, increasing the rate of reaction. This is because bile decreases the surface area of the fat, which makes it easier for the lipase to break it down.
I also believe that if I double the percentage of bile, the time taken for the fat to break down will half. This is because doubling the bile will halve the surface area of the fat, which will halve the time, taken for the lipase to break it down.
Monitoring the experiment will prove quite difficult because there is no way of accurately telling when the fat has been completely broken down. I will add sodium hydrogen carbonate and Phenolphthalein to my solution. Sodium hydrogen carbonate is an alkali, which will make the solution alkaline. Phenolphthalein is an indicator, which turns alkalis pink and acids colourless. The solution with the sodium hydrogen carbonate in it will be pink. When enough acid (fatty acids from the break down of fat) is produced, the solution will turn colourless. This will be judged as the end of the experiment.
I will conduct the experiment using 8 different values of bile concentration. I will not repeat my readings because with 8 results I will easily spot any anomalous results.
Method
Apparatus
8 test tubes
Test tube rack
1 ml syringe
5 cm syringe
Water bath
Water
Bile
Lipase
Boiled Lipase
Phenolphthalein
Sodium Hydrogencarbonate
Stopwatch
- Decide what concentrations of bile and water are going to be used (see mine below) and make them using a 1 ml syringe.
- Add 2.5 cm of milk (the fat) to each concentration using a 5 cm syringe.
- Add each 0.5cm of each bile solution to each test tube. With a marker pen, clearly mark each test tube with the percentage of bile solution.
- Add 3.5cm of Sodium Hydrogencarbonate (the alkali) to each test tube using a pump burette.
- Add 3 drops of Phenolphthalein (the indicator) to each test tube and shake so the whole solution is pink.
- Put each test tube in the water bath, set to your chosen temperature and leave for ten minutes so the whole solution is at the right temperature.
- Add 0.5 cm of lipase to 2 test tubes and start the stopwatch.
- After two minutes add 0.5 cm of lipase to another two test tubes and repeat until every test tube has lipase in it.
- Take down the time that each test tube turned white and subtract the necessary time from the necessary test tubes.
We did a preliminary experiment and found out that the experiment worked best at 35 C. Any higher temperature and the reaction was to quick to monitor accurately; when the temperature was lower, the reaction took to long and would not have given me enough time to complete the experiment.
The percentages of bile I decided to use are: -
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As you can see on Graph 1, when the percentage of bile is increased, the time taken for the fat to break down decreases. This is because bile breaks down fat by the process of emulsification, decreasing the surface area. This makes it much easier for lipase to chemically break down the fat.
I predicted that increasing the percentage of bile would decrease the time taken for the fat to be broken down, increasing the rate of reaction. As you can see in Graph 1, this prediction was correct. When the percentage of bile was 0%, the time taken was about 523 seconds. When the percentage of bile was increased to 4%, the time taken decreased to about 190 seconds.
I also predicted that if I doubled the percentage of bile, the time taken for the fat to break down would half. As you can see in Graph 1 when the percentage of bile was 2%, the time taken was 312 seconds. When the percentage of bile was doubled to 4%, the time taken was about 180 seconds. Although this is not exactly half, it is well within reasonable experimental error.
Evaluation
I believe that the experiment worked well because I received no anomalous results, they all were close to the line of best fit. However my results were not perfect, although all of my results were close to the line of best fit, they were not all on it.
This could be because the exact time when the colour of the solution turns from pink to white is subjective. There is not a précised point where the colour change happens.
To get round this problem a Colorimeter could be used. A colorimeter is a device, which calculates the colour intensity of a solution by sending a beam of light through it and seeing how much comes out the other side. However using a colorimeter, will make it difficult if not impossible to use a water bath, so by eliminating one problem; another one is created.
Another reason why my results aren't perfect is because a tiny change in the amount of lipase added to the solution could have altered all of my results; as the syringes are not particularly accurate. A chemical balance could be used to weigh the mass of the lipase, but the amounts of Lipase involved are so small, a very accurate balance would have to be used.
If I had to repeat the experiment again, I would do a narrower range of bile percentages, maybe go up in 0.05% instead of 0.5%. This would make it easier to identify anomalous results; and draw precise conclusions from the graph.
Nevertheless my experiment did give me results that are sufficient to give a reliable conclusion. ‘The more bile that is added to the reaction between lipase and fat, the faster the reaction takes place.' By looking at my graph I can see that there is a pattern but I cannot see quantitatively what that pattern does.
Extension
