Tests

Question 1

What is the test for reducing sugars?

Answer 1

1) add 2cm3 of the solution to a test tube
2) add equal quantities of Benedicts reagent

3) add to a 70 degree water bath for 5 mins

RESULT:
If reducing sugars are present the solution should turn orange-brown

Question 2

What is the test for non-reducing sugars?

Answer 2

1) first identify if the solution is a reducing sugar but doing the reducing sugar test
2) if there is no colour change, the solution isn’t a reducing sugar
3) add 2cm3 if the solution to 2cm3 of dilute hcl in a test tube and gently heat at 70 degrees for 5 mins- the heck with hydrolyse the disaccharide into monosaccharides
4) slowly add sodium hydrogencarbonate solution to the solution (neutralise)
5) re-test solution by adding 2cm3 of the benedicts reagent solution and add to a 70 degree water bath for 5 mins

RESULTS:
If reducing sugars are now present, the solution should turn orange-brown

Question 3

What is the test for starch?

Answer 3

1) place 2cm3 of the sample to s test tube
2) add two drops of iodine solution and shake well

RESULTS:
If starch is present, the sample should turn blue-black

Question 4

What is the test for lipids?

Answer 4

1) add 2cm3 of the sample to a test tube and add 5cm 3 of ethanol to that
2) shake test tube well till the two solutions have dissolved together
3) add 5cm3 of water to the solution and shake gently

RESULTS:
If lipids are present, the solution should be a cloudy-white colour

3*) as a control, add 5cm3 of water to 5cm3 of ethanol into a test tube and shake

RESULTS:
The solution should be colourless

Question 5

What is the test for proteins?

Answer 5

The biuret test
1) add a sample of the solution to a test tube and then add Equal quantities of sodium hydroxide solution in at room temp

2) add a few drops of very dilute copper (||) sulfate solution and mix gently

RESULTS:
If peptide bonds (and therefore proteins) are present, the sample should turn purple