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# Investigate the rate of a catalysed reaction, when altering the temperature of the solution and identify the optimum temperature.

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Introduction

INVESTIGATING THE EFFECT OF TEMPERATURE ON THE RATE OF A CATALYSED REACTION. AIM:-The aim of this investigation is to investigate the rate of a catalysed reaction, when altering the temperature of the solution and identify the optimum temperature. I will see if increasing or decreasing the temperature will make the rate of reaction faster or slower. In my experiment, I will be using the enzyme amylase and the substrate starch. What is the rate of reaction? In general, rate of reaction is defined as the amount of reactant used up per second, or the amount of product produced per second. This means that we can measure the rate of reaction by working out how the concentration of the reactant changes with time, or how the concentration of the product changes with time. The formula to work out the rate of reaction is:- RATE = Change in amount or concentration of substance Time taken There are many factors which can effect the rate of reaction. The four main factors are temperature, surface area, concentration and pH. Equation. The equation for a general rate of reaction between the substrate and enzyme is:- Enzyme + Substrate > Enzyme Substrate complex > Enzyme + Product (Transition state) The equation that I will be working on is:- Amylase + Starch > Amylase + Maltose > Amylase + Glucose What is happening in the equation is that the enzyme amylase is breaking down the starch to form glucose. It does this by breaking bonds. Glucose molecules are held together by bonds called glycosidic bonds. Loads of glucose molecules, joined together by these bonds, form starch. This type of reaction is known as Hydrolysis because one of the reactants in the reaction is water. The purpose of the water is to break and separate the glucose molecules, by joining on to the glycosidic bond. Diagram 1 shows what is happening through the reaction. Starch and Amylase. The substrate in the reaction is the starch. Starch is a polysaccharides of glucose. ...read more.

Middle

the iodine, I wouldn't know when in the period of 30 seconds, the reaction was actually over, thus giving me inaccurate results which are unreliable. Another problem with this technique was that each time I took a sample, I didn't know how much starch and amylase I was taking out of the test tube e.g. I might have taken more starch out than amylase, changing both of their concentrations in the test tube. This can effect the rate of reaction as I am introducing a new variable, and their for it would not be a fair test. Unlike the spotting tile technique, the test tube technique is much more quicker. This technique is more accurate and reliable because the iodine in the solution made it easier to clarify whether the starch was digested. This technique also pinpointed the exact time for when the reaction was over, thus giving me a more accurate result. The test tube technique does have a disadvantage, and that is the fact that the iodine is being mixed in to the solution at the time of the reaction. The purpose of the iodine is to indicate whether there is starch present in a solution. If there is starch present in the solution, and iodine is added to it, the solution shoulc go blue/black, to indicate that there is starch present. The iodine, in this reaction, acts as a competitive inhibitor. The iodine molecule has an identical three dimensional structure as the starch molecule, causing it to bind with the active site of the amylase molecule. If the iodine is joined to the amylase, it prevents the starch from binding to the amylase molecule, and so the starch can not be broken down as the iodine has taken it's place, therefore effecting the rate of reaction by slowing it down. This can effect the rate of reaction, but the problem can be resolved. ...read more.

Conclusion

This could be changed by using a mercury thermometer instead as they are the most accurate type of thermometers. After obtaining my results, I realised that I had two set of results that were completely anomalous. I am not sure what cause them to be strange, but it may have been the temperature keeping. It was difficult to keep a constant temperature and I may have mistaken the temperature on the thermometer for another temperature. For the second anomalous result, I realised I had put two drops of iodine instead of one, but I carried on with the experiment to see if it effected the rate of reaction, as iodine is an inhibitor. As the result was anomalous, the iodine had effected the outcome. I did repeat the anomalous results and obtained better readings. I didn't use the anomalous results to find an average as they were untrue, therefore unreliable. From looking at my results plotted on the graph, I could investigate further by carrying out experiments in between the range of temperatures, where the optimum temperature lies, to pinpoint exactly where the optimum temperature is. To see whether my conclusions are correct, I could set up another different experiment, for the same variable to see whether I get a similar pattern. I could do this in many ways. I could use the same volumes of starch, amylase and iodine, but apply the changes I made earlier. I could use a more accurate measuring pipette for the iodine, use set temperature water baths, use a starch suspension which is true and making it true where all the starch and amylase is equally distributed in the solution. I could also use the colourimiter to pinpoint exactly when the reaction is over. From the analysis of my results and method, I can't say that my results are 100% accurate and reliable, but I could investigate further in many ways by creating different experiments, which will give me a more accurate reliable set of results and a conclusion which is 100% reliable. ...read more.

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