Organic Chemistry

Biuret Test for Proteins

Purpose:  To test for presence of proteins

Materials:  Samples (ie. Egg white, milk, casein solution), 1M NaOH, .125M CuSO4.distilled water, test tubes pipettes


·      Add samples to separate test tubes

·      Add distilled water to the samples

·      Drop about 4 drops of sodium hydroxide to each sample

·      Add as much copper sulfate as needed and stir

·      Make a test tube with water, sodium hydroxide, and copper sulfate as a blank


            The egg stuck to itself and wanted to glob together, rather than pouring evenly.  When the distilled water was added, the egg stayed together in long, swirling strands. The water mixed evenly with the milk and the clear casein solution.  When the copper sulfate was added to the egg, the turquoise solution slowly spread and became slightly pink.  Within a matter of seconds after being stirred, the solution became purple.  When the copper sulfate was added to the milk, once again, the turquoise slowly spread and when it was stirred, it became lavender/purple.  The casein solution slowly turned a translucent purple when the copper sulfate was added.  The blank kept the turquoise color.