Biological tests

• Used to identify reducing sugars (monosaccharides and some disaccharides) 
• Add Benedict's solution to the chemical sample and heat.
• The solution changes from blue to brick-red yellow if a reducing sugar is present. 

• Used to test for non-reducing sugars, e.g. the disaccharide, sucrose 
• 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 hydrogen carbonate. 
• This breaks the glycosidic bond of the disaccharide, releasing the monomers. 
• 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 bliue-black 

All the biochemical tests need to be learned. This work is good value because they are regularly tested in 2 or 3 mark quaetion components. 

• Used to identify fats and oils 
• Add ethanol to the sample, shake, then pour the mixture into water.
• If fats or oils are present then a white emulsion appears at the surface. 

• used to identify any protein 
• Add dilute sodium hydroxide and dilute copper sulohate to the sample. 
• A violet colour appears if a protein is present.