The particles need to collide for a reaction to take place, which is why the rate of reaction depends on how well and often the particles collide with one another. When the temperature is increased, then all of the particles will move more quickly. This means that if they are all moving faster, then there will be more collisions with one another.
The three theories/rules that will help me to understand this investigation are the Kinetic theory, the 10o rule and the Arrhenius theory. The Kinetic theory would help me as the molecules will need to collide to react, so that is teaching me why they have to collide with each other. The 10o rule will help me to understand this investigation because it teaches that as the temperature increases by roughly 10oC, then the rate of reaction time will also roughly double. Also the Arrhenius theory helps me as it teaches that increasing the temperature makes the molecules move around much faster.
Preliminary Work
In the investigation, we had to carry out some preliminary work. Firstly, I had to find out the right volume of renin and milk that I would be using in this investigation to make it a success. For me to do this, I had to put a certain volume of renin and a certain volume of milk into a test tube. I then varied the volumes of renin and milk again and put it into another test tube, which I repeated about 3 more times. I then heated each of these test tubes by putting them into separate water baths with different temperatures. Then you add the renin into the test tube with the milk in it and then you time how long it takes for the milk to clot. If it takes too long to clot, then the volume of renin and milk that I had chosen would not be a useful experiment. That is why I chose the right amount of renin and milk for the investigation. The preliminary test was a good way for us to work out the right volumes to use for the investigation.
Apparatus List
- Up to 10ml of milk
- Up to 1 ml of renin
- Beaker
-
4 test tubes – so that we could carry out 2 experiments at the same time
- Test tube rack
- Measuring Cylinder
- Syringe
- Digital stop clock
-
Thermometer – showed us the temperatures of the test tubes while they were in the water baths
-
Water bath – a constant temperature was kept in each separate water bath. This was effective as we did not require the use of a Bunsen burner, which could have led to difficulties with the variation of the different temperatures.
Method
Firstly, I had to measure 0.4 ml of renin using a syringe and squirted it into a test tube. Now I had to measure 4ml of milk using another measuring cylinder and then poured that into another different test tube. Now I had to place these to test tubes into the first water bath. Then when they had reached the required temperature I took them out. I was able to no whether they had reached the right temperature as the thermometer read the right temperature.
Then we got the stop clock ready and poured the renin into the test tube with the milk in it. I put the test tube back into the water bath and then got another person who was working in my group to press the start button on the stop clock.
Once this had been done, we repeated the experiment again and then recorded an average. It was good that we repeated the experiment just in case we found an odd result. The same method was used with the other experiments.
Variables
In this investigation there is only 1 variable and this is the temperature. This is the only variable in this experiment because this is going to be the only thing in the investigation that we are going to change around. We will be keeping the same volume of renin and milk throughout the investigation and only this will change. After our preliminary testing, we found that the temperatures that the renin would not work at would be anything around 70oC and it would take to long for the renin to work at a temperature too below body temperature (37oC). Therefore we decided to investigate the rate of reaction between the renin enzyme and the milk at the temperatures of 25oC, 30oC, 40oC, 50oC and 60oC.
Fair Testing
To make sure that this investigation was a fair one, we had to do some things to keep this investigation fair and to make sure that our results were not wrong.
Firstly, we needed to make sure that we were using the same type of milk, e.g. semi-skimmed milk. It is important that the same type of milk is used throughout the investigation. Different type milk could effect the time in which it takes to clot. Also it is important to keep the same amount of renin and milk for each experiment. An increase in milk or renin could alter the results and give an odd result on the graph.
Also make sure that the thermometer reads the same each time when it is in the water baths. If the thermometer was not at the same temperature as it was in a previous experiment it could make a difference in the results. It would also be recommended that the same person starts and stops the digital stop clock. This is because another person might not have the same reaction speed and therefore could not stop the clock on time and the time taken for the milk to clot could be slightly quicker or slightly slower.
Results Table
Here is the result table that I got for using 3ml of milk and 0.5 of renin.
Analysis
After I had completed this investigation, I had noticed that the renin works best at between 40oC and 50oC. This is because at this temperature the enzymes are moving faster and therefore there are more collisions and that causes the milk to clot quickly. I noticed that the renin worked at its slowest at the temperatures of 25oC and 60oC. I think this is because the enzymes are moving around very slowly and fewer collisions are taking place due to this. They also do not work at 25oC because it is too cool a temperature and they do not work at all at a temperature that is above 60oC because they will have denatured by this time. From my results I have noticed that between 25oC and 40oC the time it takes for the milk to clot gets less, but then once you to 50oC it begins to get slower until it gets to 60oC when it stops clotting completely.
Therefore my prediction that I made was correct when I said that the renin will take longer to react and make the milk clot when the temperature is low. I also said that when the temperature increases, the time it takes for the milk to clot will decrease and that the renin will work its best at around about 40oC. I was right in saying that once the temperature exceeds about 60oC, then the renin would not work and therefore the milk would not clot. This is due to the enzyme denaturing.
As you can see, I was wrong when I said that the Arrhenius theory would occur during this investigation. This is because; the Arrhenius theory says that if you increase the temperature by 10oC, then you will double the rate of reaction. This means that it will take half the time for the reaction to take place. Here is an example.
As you can see, the average time for 30oC was 638 seconds. For the Arrhenius theory to work then the average time for 40oC would have to be 319 and as you can see, it only was 79! There is a massive gap in between the two and therefore the Arrhenius theory did not work in this case. Also at 40oC the average time was 81seconds and for the Arrhenius theory to work, the average time for 50oC would have to be 40.5 or 41, but as you can see it was 96. It also shows that the right time for the renin to work was around 40oC, because after 50oC, the average time increases.
Evaluation
In the investigation, there where two odd results that occurred. The first was at 30oC where at the first test the time taken for the milk to clot was 572 seconds and in the second test the time taken was 703, which is nearly 3 minutes difference. The second was at 50oC. The first result I got was 177 seconds and then from the second test the result was 96 seconds. The margin here was almost double between the two test times! I believe that this could have been caused by me not measuring the correct amount of renin, milk or I might not have got the temperature precisely right, but these problems could have occurred in any of my results as the equipment that we used was not of a great quality. For example, the syringes, they were not very good to use at all. I continuously found it difficult to suck up the renin. I believe that this might be because the syringe was also sucking air at the same time and this might have made it difficult to get the correct amount of renin into the syringe and then therefore into the experiment.
I believe that there were a few minor problems with the method of the investigation. One would be the quality of the equipment that we were using. For example, the syringes, they were not very good to use at all. I continuously found it difficult to suck up the renin. Also we should have been able to get the renin into the milk test tube in the water bath without the renin losing the heat that it had. Then again, I would find it rather difficult to come up with a way to solve that problem.
If we had to do this investigation again, I would make sure that we had better quality equipment to do the investigation. I would also like to make sure that the milk had not clotted without me being aware of it, so therefore I probably would have to pay a bit more attention to the milk to make sure that I did not miss when it was clotting.