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C O L O R I M E T RY & T H E B E N E D I C T ’ S T E S T

Recall what a qualitative test tells you: This kind of test determines the presence of something in a sample, but not the amount of it.

You can use Benedict’s reagent and a colorimeter to get a quantitative estimate of how much glucose (or other reducing sugar) there is in a solution.

A colorimeter is a device that measures the strength of a coloured solution.

• It measures how much light passes through the solution.
• It measures the absorbance – the amount of light absorbed by the

The more concentrated

the solution, the higher

the absorbance.

To find out the concentration of glucose in an unknown solution, you need to carry out a serial dilution. A serial dilution involves making up several solutions of known glucose concentrations. You then measure the light absorbance of each dilution after doing the Benedict’s test on each one in a standardised way.

Once you have made up your serial dilutions of glucose, the following steps can be carried out:

YOU WILL NOW CARRY OUT A VERSION OF THIS PRACTICAL TO FIND OUT THE CONCENTRATION OF AN UNKNOWN GLUCOSE SOLUTION (IN YOUR PRACTICAL LAB BOOKS)