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Tests for carbohydrates
Benedict's test used to identify reducing sugars (monosaccharides
and some disaccharides)
1) Add Benedict's solution to the chemical sample and heat.
2) The solution changes from blue to brick-red or yellow if a
reducing sugar is present.
Non-reducing sugar test used to test for non-reducing sugars, e.g. the
First a Benedict's test is performed.
If the Benedict's test is negative, the sample is hydrolysed by
heating with hydrochloric acid, then neutralised with sodium
This breaks the glycosidic bond of the disaccharide, releasing the
A second Benedict's test is performed which will be positive
because the monomers are now free.
Add iodine solution to the sample.
If starch is present the colour changes to blue-black.
Tests for lipids
Emulsion test used to identify fats and oils
Add ethanol to the sample, shake, then pour the mixture into
If fats or oils are present then a white emulsion appears at the
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Tests for proteins in the laboratory
Biuret test used to identify any protein
Add dilute sodium hydroxide and dilute copper sulphate to the
A violet colour appears if a protein is present.…read more