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A Colorimetric method for the estimation of glucose (or reducing sugars) in solution.

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Introduction

Rikin Patel A Colorimetric method for the estimation of glucose (or reducing sugars) in solution. Aim: the aim of phase one of the experiments is to devise a method of measuring the concentration of glucose in a solution. Two mystery substances will be used to check if the method is correct. This will tie in with phase two of the experiment, which is to find the rate of the activity of the enzyme invertase. (The enzyme invertase catalyses the reaction: Sucrose Fructose + Glucose) i.e. the product of invertase are reducing sugars. Information on phase 1: glucose, a reducing agent will reduce an acidified purple pink solution of potassium manganate to a colorless solution of manganese ions. The partial ionic equation is: Mn0 + 8H + 5e Mn2 + 4H20 The time taken for the loss of colure from a standard solution of permanganate is directly related to the concentration of glucose present in solution. The results will be plotted on an assay curve. From this curve the results of the mystery substances can be measure to see if the procedure of measuring the concentration of glucose in a solution is correct. Method for phase 1&2: 1. Using the plastic syringes introduce 10cm3 glucose solution and 5cm3 sulphuric acid into a flat-bottomed tube.

Middle

Dependant variables- this is another area of the experiment where inaccuracy can occur. The dependant variables in this experiment is the time it takes the solution to decolourise. In order for the experiment to be fair the point of decolourisation has to be defined. This can be done by using a white piece of paper and putting it behind the test tube and compare the solution to the paper. Fixed variables: in order for the experiment to be fair these factors need to be taken into consideration. Temperature, volumes of sulphuric acid, volume of potassium mangante and the glucose and water. The volumes of the sulphuric acid and potassium mangante have to be taken accurately for the experiment to be fair. The timing of the stopwatch also has to be accurate. All these factors need to be controlled if the experiment is to be fair. The main observations in this experiment are the colour changes from purple to clear. This will be done with the naked eye and it is in this area where faults in accuracy are most likely to occur. To stop inaccuracy the introduction of white paper behind the test tubes can help determine when the solution has decolourised. The measurements of the results will be changed from the numerical numbers received on the stopwatch to seconds.

Conclusion

The table will have the various concentrations of glucose for phase one along the top and the times of decolurisation along the sides. The same procedure will occur for the data logging as phase one except along the top will be the various time of the concentration. Due to the lack of time in the double lesson to contain all the results the use of concurrent time recording will be done so that all the results can be recoded and finished in the time allocated. If this process is to occur the experiment needs to be organized well, therefore the equipment needs to be set out accurately and efficiently. Data Analysis: To analyse the data of both phases of the experiment the data will be put into graphs. By plotting the data on the graphs we can work out the concentration of the mystery substance by using the curve in the assay graph. By plotting the graph for phase to we can then produce a gradient line. This will then therefore allow us to work out the rate of enzyme activity. This is what is predicted for the graph of phase 1: 1) Assay Curve 2) This is the prediction of the graph for phase 2. Line of Gradient 3) by using the line of gradient form the graph above we can then work out the Rate of enzyme activity.

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