Testing for chemicals

Test for reducing sugars

Test for reducing sugars

Benedict’s test

• add benedict’s solution (blue)

• boil in water bath

• positive = brick red + red brown precipitate

Test for protein

Biuret reagent

sodium hydroxide + copper sulfate = biurets reagent - light blue

positive = mauve (purple)

Test for lipids

• add ethanol

• mix vigorously

• add water

• positive = white emulsion / suspension. NOT precipitate

Test for starch

• a few drops of iodine

• positive = blue black

Emulsion vs precipitate

emulsion : 2 solutions that are mixed but don’t form a single layer

precipitate : solid suspended in liquid

Reducing sugar and examples

loses electrons

eg, glucose, fructose, lactose, maltose