Tests for the presence of carbohydrates, proteins and lipids. By Sophie Fox

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STARCH

  • Add a solution of iodine (in potassium iodide).
  • The iodine solution changes from yellow to blue/black.

REDUCING SUGARS

  • Heat with Benedict's solution (alkaline copper sulfate).
  • The colour changes from blue to orange/red.
  • A precipitate is formed.

NON-REDUCING SUGARS

  • The non-reducing sugar will not react with the Benedict's solution.
  • Boil the sample with hydrochloric acid.
  • This hydrolyses any sucrose present, splitting sucrose molecules to give glucose and fructose monosaccharides.
  • Cool

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