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A Colorimetric Method for the Estimation of Glucose in Solution.

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Introduction

A Colorimetric Method for the Estimation of Glucose in Solution Method A clean pipette was used to transfer 10cm of 10% glucose into a boiling tube. The pipette was then used to transfer 9cm of 10% glucose into a different boiling tube. 1 cm of distilled water was added to give 10cm of 9% glucose. This was repeated to make 10cm of 8%, 7%, 6%, 5%, 4%, 3%, 2%, and 1% glucose solutions (use the table below to help): Concentration of glucose (%) Volume of 10% glucose to transfer (cm ) Volume of distilled water to transfer (cm ) Total volume of solution (cm ) 10 10 0 10 9 9 1 10 8 8 2 10 7 7 3 10 6 6 4 10 5 5 5 10 4 4 6 10 3 3 7 10 2 2 8 10 1 1 9 10 A clean pipette was used to transfer 5 cm of 1M sulphuric acid into each solution. A clean pipette and pipette filler was used to transfer 2cm of potassium permanganate solution into each boiling tube. ...read more.

Middle

The timer was then stopped only when the solution became completely clear. From completing the experiment and producing the graph it is possible to deduce that the lower the strength of the solution the more time it takes for complete decolourisation of potassium permanganate. This means that the time of the reaction is dependent on the concentration. Evaluation Problems first occurred in making the glucose solutions. The problem was that an extra 1cm of 10% glucose was added due to confusion with the pipette. This may have been prevented if a syringe had been used. However the pipette gives greater accuracy. The next problem occurred when the potassium permanganate did not completely mix with the acidified solution, due to the potassium permanganate being added too quickly in an attempt to make sure that it was added all at once and fairly. This meant that there was some potassium permanganate that was not being decolourised. This led to some of the results being marginally slower than they should have been. ...read more.

Conclusion

Possible reasons for the errors causing these anomalous are that not all of the potassium permanganate fully mixed causing only partial complete decolourisation while there is still a layer of deep purple coloured potassium permanganate above it. An additional problem occurs in that the end point may not have been completely reached or may have passed; in either case the time recorded will have been incorrect. There are limitations to this procedure, e.g. the timer is not precise enough therefore leading to results that are not sufficiently accurate to get perfect results. This could be improved by using a more accurate timer, or maybe timers, then find the average time elapsed. A separate limitation would occur if there were not enough results to procure a correct conclusion. One improvement would be to collect a large varied selection of results; this would mean that there would be more evidence to corroborate the conclusion. These limitations, if not resolved, may result in error. The experiment could improve by using a less subjective method; this could be done by reducing the intricacy of the method. This would lead to the method being easier to follow therefore increasing the ability of obtaining improved results ...read more.

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A good account of the investigation with a focus on results and evaluation. Some background to the technique used and, in places, a little more detail would improve the quality of this work.

Marked by teacher Adam Roberts 20/08/2013

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