RP11 - Measuring the Concentration of Glucose using a Calibration Curve

Question 1

How can Benedict’s solution be used to measure the concentration of glucose in
a solution?

Answer 1

Use a colorimeter to measure the absorbance of
a series of solutions of known concentrations to
create a calibration curve. Compare the absorbance of an unknown sample to the
calibration curve.

Question 2

What is a serial dilution?

Answer 2

A dilution where successive

concentrations increase/ decrease in a logarithmic fashion

Question 3

Outline the procedure of this practical.

Answer 3

1. Make a serial dilution of glucose, ranging from 0 to 10 mmol dm-3 .
2. Place 2 cm3 of each of the unknown samples in separate boiling tubes.
3. Add 2 cm3 of Benedict’s solution to all boiling tubes.
4. Place boiling tubes in a water bath at 90°C for 4 mins.
5. Zero the colorimeter using a cuvette with distilled water and set to red filter.
6. Place known samples into cuvette and measure the absorbance of each using the colorimeter.
7. Make a calibration curve.
8. Measure the absorbance of the unknown samples using the colorimeter.
9. Use the calibration curve to determine glucose concentrations.

Question 4

What are the axes in a calibration curve?

Answer 4

Absorbance against glucose

concentration

Question 5

What would a high glucose concentration in urine suggest?

Answer 5

It may suggest diabetes. Lack of insulin leads to high
blood glucose conc, hence high concentration in the glomerular filtrate, so not all
glucose can be reabsorbed in the proximal convoluted tubule.

Question 6

State the hazards and precautions of this practical.

Answer 6

Benedict’s solution is an irritant, wear eye protection, avoid contact with skin.
Handle the hot water bath with care.

Question 7

How can you increase the accuracy of the estimate of the unknown glucose solution?

Answer 7

Increase the number of concentrations (at smaller intervals) for the calibration
curve within the range of concentrations that the unknown solution belongs in.