Colorimeter

Question 1

How to use a colorimeter

Answer 1

1. Switch the colorimeter on and leave to stabilise for 5 minutes.
2. Select the red filter (for Benedict’s – use a complementary colour to starting solution)
3. Set the colorimeter to zero using a cuvette 3⁄4 filled with distilled water.
4. Ensure the cuvette is placed into the colorimeter so the light passes through the clear sides.
5. Make sure the slides are clean and there are no bubbles in the solution.
6. Using a pipette, fill the cuvette 3⁄4 with the sample.
7. Place in the colorimeter and read the absorbance of light.
8. Less light is absorbed by the solution in a paler solution, so there is a greater transmission for a paler solution’s

Question 2

To measure the concentration of a solution (commonly of reducing sugars) using a colorimeter, a calibration curve is used. This is produced in the following method:

Answer 2

Standard solutions of the reducing sugar should be used. Standard solutions are those of known concentration.

2. Carry out a Benedict’s test on each sample (the Benedict’s solution must be in excess).
3. With the colorimeter, measure the percentage transmission for each sample.
4. Plot a graph of transmission against reducing sugar concentration.

Question 3

The paler the solution…

Answer 3

Lower absorbance + higher transmission

Question 4

What indicates a higher reducing sugar concentration

Answer 4

High absorbance + low transmission