3.1-7 Biological molecules tests

Question 1

What is the Benedicts test used to test for?

Answer 1

• reducing and non-reducing sugars

Question 2

What is a reducing sugar?

Answer 2

• is one which can donate electrons and all monosaccharides and some disaccharides

Question 3

What is the method used for the Benedicts test?

Answer 3

• an
  alkaline solution of blue copper (II) sulphate is added to the sugar and subsequently
  heated
• in the presence of reducing sugar, a red precipitate of copper (I) oxide is
  formed
• in the absence of reducing sugar, the Benedict’s reagent does not change
  colour

Question 4

What is the Biuret test used to test for?

Answer 4

• proteins

Question 5

What is the method used for the Biuret test?

Answer 5

• a sample of the solution is placed
  in a test tube and subsequently an equal amount of NaOH is added
• afterwards, a few
  drops of dilute copper (II) sulfate solution is added and gently mixed
• in the presence
  of a protein, the solution turns lilac/ as an indicator of peptide bonds.
• in the absence
  of protein, the solution remains blue

Question 6

What is the Emulsion test used to test for?

Answer 6

• lipids

Question 7

What is the method used for the Emulsion test?

Answer 7

• ,2ml of sample is added to 5ml of
  ethanol
• subsequently, the contents are mixed thoroughly by shaking to ensure that
  the lipids dissolved
• upon addition of 5ml of water and mixing, the solution turns
  cloudy indicating the presence of lipid due to the formation of an emulsion where the
  light is refracted as it passes from droplets of oil to droplets of water.

Question 8

What is the Iodine test used to test for?

Answer 8

• starch

Question 9

What is the method used for the Iodine test?

Answer 9

• in the presence of starch, the colour of
  potassium iodide solution from yellow to black/blue