5.2 Glucose Concentration

Question 1

Method for determining glucose concentration

Answer 1

1. Add 10cm3 of 1% glucose sol in a beaker
2. Make serial dilution (glucose in distilled) water for concs: 1, 0.5, 0.25, 0.13, 0.06
3. label 7 tubes including 0.0 & unknown
4. Add 1cm3 of each glucose conc to each test tube (Distilled water in 0.0) Using a separate pipette each time
5. Add equal quantity 1cm3 Benedict reagent to each tube
6. Add pea sized anti bumping granules
7. Place boiling tubes into 100.C water bath for no longer than 5 minutes Then remove and let them cool
8. filter out the precipitate in each tube
9. Set the colorimeter to red light and use 0.0 concentration to set 100% transmission
10. pipette each filtered solution into a cuvette, Measure transmission and record
11. Create a calibration curve and use it to find unknown glucose concentration.

Question 2

Why does transmission of red light increase as glucose concentration increases

Answer 2

When there is more glucose, there is less cu from the Benedict’s reagent left As it has reacted with the reducing sugar therefore less light is absorbed and more is transmitted

Question 3

Why is it necessary to filter the sample before taking the reading of the colorimeter

Answer 3

To make sure there is no solids left in the solution eg anti bumping granules which may absorb some of the lights and change the accuracy of the results

Question 4

If the reading for unknown glucose solution is higher than a concentration of 1%, what could you do to obtain an accurate value

Answer 4

Continue on the graph with a dotted line or repeat the investigation with higher values of concentration for a more accurate result

Question 5

What is the difference between the quantitative test and qualitative test

Answer 5

Quantitative test can tell us the measure of something in the solution
Qualitative test just tells us positive or negative result

Question 6

How can we use the calibration curve to estimate glucose concentration

Answer 6

Find the absorbency/ Transmission using the colorimeter three times to find a mean. then read off the value on the graph that matches the absorbency, draw a line across and down

Question 7

How can we calibrate using a colorimeter to measure the concentration of a reducing sugar in an unknown sample

Answer 7

• Set the colorimeter to zero using a red filter
• use known concentration of lactose and produce a serial dilution
• do the test for reducing sugars for each know concentration and write down the results of the colorimeter to produce a calibration curve
• test the unknown sample using the same method, find its absorbency
• then use the curve and read off the value of absorbency to determine concentration