Colorimetry For Determining Concentration Of A Glucose Solution

Question 1

What is a colorimeter?

Answer 1

A device that measures the strength of a coloured solution by seeing how much light passes through it

Question 2

What does a colorimeter measure?

Answer 2

The absorbance of solution. More concentrated the colour, the higher the absorbance is.

Question 3

In terms of using the benedicts test, what do you use for the colorimeter and what results would you expect to see?

Answer 3

• Use the blue benedicts solution that’s left after the test
• The paler the solution, the more glucose there was that was turned into a precipitate
• The higher the glucose concentration, the lower the absorbance of the solution

Question 4

What are the steps to carrying out the test for determining glucose concentration in a solution?

Answer 4

1) Have 5 samples of known glucose concentration solutions: this can be done by the serial dilution technique:
- add 10cm3 of initial 40M glucose solution in one test tube and 5cm3 of distilled water in all the others
- draw 5cm3 from test tube 1 and add to test tube 2 =10cm3 of solution which is half as concentrated
- repeat process 3 more times, creating solutions which are half as concentrated as the previous one (40M, 20M, 10M, 5M, 2.5M)

2) do benedicts test on all solution including a control tube of pure water
3) remove precipitate/ remaining benedicts solution to put in cuvettes
4) use colorimeter with a red filter to measure absorbance of remaining benedicts solution from each tube
5) use results to draw a calibration curve, showing absorbance against glucose concentration. Line of best fit can then be used to indicate glucose concentration of unknown samples