Aim : To determine whether given unknown solutions A,B,C,D,E,F and G contain Reducing/NonReducing Sugars, Lipids, Proteins or Starch.
Apparatus/Materials: - Bunsen burner
- Solutions A, B, C, D, E, F and G (unknown)
- Measuring Syringes
- Stirring Rod
- Test tubes (7)plus holder and tray
- Copper sulphate solution (CuSO4)
- White dropping ray
- tripod stand and mesh
- Biuret͛s solution
- Sodium Hydroxide solution (NaOH) (or Potassium Hydroxide solution) - Hydrochloric Acid (HCl)
- Sodium Hydrogencarbonate (NaHCO3)
- Iodine Solution(I2) (or Potassium Iodide solution)
- Ethanol (C2H5OH)
- distilled water (H2O)
Reducing Sugars 2cm3 of solutions A-G were placed into separate, labelled test tubes using separate measuring syringes. An equal volume
(2cm3) of Benedict͛s solution was then added to the solutions in the test tubes. The tubes were then gently shaken and placed in a water bath until any possible change in colour was noticed.
A- changed from a transparent bluish colour to purple. B- changed from a bluish colour to a yellow orange colour from the surface; middle began turning green; then entire solution turned bright orange in colour.
C- turned from blue to a dark blue/purple.
D- no reaction
E- no reaction
F- changed from a bluish colour to a yellow orange colour from the surface; middle began turning green; then entire solution turned bright orange in colour.
G- no reaction.
Benedict͛s solution contains copper sulphate.Reducing
Sugars reduce soluble blue copper sulphate, containing copper (II) ions (Cu2+) to insoluble red-brown copper oxide containing copper (I).
The latter is seen as a precipitate. Therefore, solutions containing reducing sugars were: B and F.
Those not containing reducing sugars were: A, C,
D, E, and G.