Practical Skills : Colorimetry

Question 1

Colorimeter used for :

Answer 1

• determine the concentration of a glucose solution
• use Benedict reagent & colorimeter get qualitative estimate - how much glucose / reducing agents are in solution
• colorimeter- measure strength of coloured solution by seeing light pass through / measures the absorbance ( light) more concentrated- more absorbance
  Paler solution more glucose concentration- higher glucose conc - lower absorbance

Question 2

How to carry out the practical : colorimetry

Answer 2

1. Make up several glucose solutions of different known concentrations - serial dilution techniques
   2 . Line up test tubes in a rack - add 10cm3 of initial 40mM glucose solution to first test tube & add 5cm3 of distilled water to other tubes
2. Draw 5cm3 solution using pipettes - add to 2nd tube - mix thoroughly - now in 2 tube have 10cm3 of 20mM glucose concentration- repeat process 3 more times make 10,5,2.5 mM
   Make calibration curve :
3. Benedict test for each solution ( plus negative control of our water ) - same Benedict solution for each case
4. Remove any precipitate - leave for 24hrs or centrifuge
5. Use colorimeter with read filter - measure absorbance of Benedict solution remaining in tube
6. Use results make calibration curve - absorbance against glucose concentration
   - then test for unknown solution