Determining glucose concentration

Question 1

Briefly outline how you would determine glucose concentration

Answer 1

1) Make a dilution series of glucose in distilled water
2) Add corresponding glucose concentration to each tube
3) Add distilled water to 0.00% tube
4) Add Benedict’s reagent
5) Place boiling tubes into the water bath
6) Pipette small volume of each solution into a centrifuge tube and centrifuge
7) Set up a colorimeter

Question 2

Outline how you would find unknown glucose concentration from a colorimeter

Answer 2

1) Set red light on colorimeter
2) Distilled water in a cuvette
3) Pipette supernatant into a clean cuvette
4) Measure/record transmission
5) Create a calibration curve
6) Find glucose conc. using the curve

Question 3

Does transmission of red light increase or decrease as glucose concentration increases?

Answer 3

Increases

The solution becomes clearer, allowing more red light to pass through the solution

Question 4

Why is it important to centrifuge the solutions?

Answer 4

To remove the precipitate

Precipitate/suspended particles will scatter light

Question 5

Why does Benedict’s reagent go from blue to red?

Answer 5

The reducing sugar reduces Cu2+ into Cu+

Cu2O is brick red

Question 6

Outline how you would carry out a non-reducing sugar test

Answer 6

1) Add equal volumes of HCl
2) Add sodium hydrogencarbonate
3) Add Benedict’s reagent

Question 7

What colour changes will take place if a non-reducing sugar is present?

Answer 7

Yellow-orange-brown-brick red

Question 8

Why do you add sodium hydrogencarbonate when testing for a non-reducing sugar?

Answer 8

To neutralise the added acid (HCl)

Question 9

Outline the Benedict’s test

Answer 9

1) Add equal volume of Benedict’s reagent and solution to be tested
2) Heat in a boiling water bath
3) Observe colour of precipitate formed