1.2 Biochemical Tests

Question 1

What is the test for Starch and what are the colours?

Answer 1

Iodine
Orange to blue/black

Question 2

What is the test for proteins and what are the colour changes?

Answer 2

Biuret reagent
Blue to purple

Question 3

What is the test for Lipids and what are the colour changes?

Answer 3

Dissolved in ethanol and distilled water
Turns to a cloudy white emulsion

Question 4

Name the only non reducing sugar

Answer 4

Sucrose

Question 5

What is a reducing sugar?

Answer 5

A sugar with a reducing group able to reduce the copper sulphate in benidicts solution

Question 6

What does copper sulphate turn to when reduced?

Answer 6

Copper oxide

Question 7

What is a non reducing sugar?

Answer 7

A sugar unable to reduce copper sulphate due to its reducing group being bonded in a glycosidic bond

Question 8

What is the test for reducing sugars and what are the colour changes?

Answer 8

Benedict’s solution and heat
Brick red

Question 9

Rank the colour changes of Benedict’s solution in order of concentration

Answer 9

Highest——————Lowest
Brick red, Orange, Yellow, Green

Question 10

What are the steps to test the presence of non reducing sugars?

Answer 10

1. Confirm by testing Benedict’s solution again
2. Add acid and boil to 100•C
3. Cool
4. Add alkali
5. Repeat Benedict’s test with heat to see result

Question 11

What is the process of adding acid called?

Answer 11

Acid hydrolysis

Question 12

What is the alkali used in the test for non reducing sugars and why is it necessary

Answer 12

Sodium hydrogen-carbonate
To neutralise the acid

Question 13

What does adding acid do to a non reducing sugar?

Answer 13

Breaks down the glycosidic bond to free the reducing group