To test for protein, you added Biuret solution and

observed color changes. Suppose that the color

data below was observed.

Gelatin

( + Control)

Pink/purple

Water

(-Control)

Pink/purple

Mystery Food

Sample

Blue

The data above indicate an error. How do you

know? What might have caused the error?

Water sample showing pink/purple color is an error.

Explanation:

Biuret is a blue color reagent that changes its color to pink/purple whenever it detects protein in a sample. Water don't contain proteins so it should not show pink/purple color instead it should maintain the blue color. Food items generally contain proteins so it show pink/purple color but it showed blue color.

Error might have caused by wrong marking of the samples, test tube marked with Water might contain a mystery food while Mystery food tube might contain water.

The water should not be pink/purple because water should test negative for protein.

The water should actually have turned blue, because Biuret solution is blue.

Someone may have mislabeled the test tube with water.

The water may have been contaminated with a protein.