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Quantative analysis of glucose using a colorimeter

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Introduction

Experiment: Quantative analysis of glucose using a colorimeter Apparatus 6 concentrations of glucose Test tubes Test tube racks Couvettes Water bath Colorimeter Syringe Risk assessment Lab coat because using Benedicts solution = corrosive Safety glasses because using Benedicts = corrosive Hair tyed back out of the way Bags under the desk out of the way Method There are six concentrations of glucose solution: 0.01%, 0.05%, 0.1%, 0.25%, 0.3% and x. The aim is to find the concentration of x. A control is also to be completed. A control is a sample used to compare the results collected. To do the control, the same volumes are used as in the other samples: 2cm3; 1cm3 of Benedicts solution and 1cm3 of distilled water. The other 6 concentrations were then mixed with Benedicts solution, each to the ratio 1cm3:1cm3 of Benedicts:glucose solution. Label each test tube with the concentration of glucose and then place them in the test tube rack. ...read more.

Middle

Everytime a new sample is measured, reset the colorimeter using the "reset to 0" button. Pressing this button will make each experiment a fair test. Pour the solutions from the test tubes into the couvettes. Then reset the colorimeter and and slide the couvette into the colorimeter according to the direction the light was shining. Then read off the results and record it in the table. Results Concentration % Transmission % Colour of solution Control, 0 85 Blue 0.01 66 Blue 0.05 41 Greeny/blue 0.1 25 Brown 0.25 12 Orange 0.3 9 Red x 31 Greeny/blue Conclusion There was approximately 5 sources of error in my experiment. Firstly I found the syringes and measuring cylinder to be innaccurate. It was difficult to measure out 1cm3 everytime. I think the amount of drops of Benedicts solution should have been counted. The measuring gauge was difficult to read and an extra drop in one sample may cause the results to be unreliable. ...read more.

Conclusion

This meant that when the solution was poured into the couvettes, the precipitate was still in the bottom of the test tube and this precipitate was vital and needed to be tested. The solution needed stirring before being transferred to the couvette to prevent all of the pecipitate from being left in the bottom of the test tube. The last source of error I noticed was the "0" on the colorimeter may have fluctuated meaning the dial did not reset to "0" everytime. I think the colour of the solution, CuO, changed because the aldehyde group of the aldose sugars reduced Cu II to Cu I. The aldehyde group oxidised to form a carboxyl group causing the colour to change as the structure of the molecule changed. This practical is used in the food industry and for medical reasons. The food industry use it widely to improve their products, for example they know how concentrate to make chocolate to make it how the public enjoy it. It is used in medicine to test urine for diabetes or sugar defects. I think that concentration x = 0.075% ...read more.

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