Practical: Testing for Biological Molecules

What reagent is used to test for reducing sugars in a sample?

Benedict's Reagent.

What color does Benedict's Reagent start as before testing for sugars?

Blue.

What is the color change in the precipitate when reducing sugars are present, starting from no sugar?

Blue → green → yellow → orange → brick red.

What is the first step in the Biuret Test for proteins?

Add a few drops of potassium hydroxide solution to make the solution alkaline.

What color indicates the presence of protein in the Biuret Test?

Purple.

What happens to the solution in the Biuret Test if no protein is present?

The solution will stay blue.

How do you test for lipids using the Emulsion Test?

Shake the test substance with ethanol, then pour into water.

What does a milky emulsion indicate in the Emulsion Test?

Lipids are present.

What color change indicates the presence of starch when iodine is added to a sample?

Browny-orange → dark blue-black.

What safety precaution should be taken when using iodine in testing?

Wear goggles as iodine is an irritant to the eyes.

What should you do immediately if you spill any chemicals used in the Biuret Test on your skin?

Wash it off straight away.

What should you be cautious of when working with the water bath in the Benedict's test?

It can be hot, so be careful around it.