Testing for Biological Molecules Flashcards
How can you test for sugars?
Use Benedict’s Reagent (blue) - add to a sample, heat it to 75°C.
What colours does Benedict’s Reagent go?
If present - forms a coloured precipitate (the colours range from green, which is a low concentration, to brick red, which is a high concentration).
If not - stays blue.
How can you test for starch?
Use Iodine solution (browny-orange).
What colours does Iodine solution go?
If present - changes to a dark, blue-black colour.
If not - stays browny-orange.
How can you test for lipids?
Use the Emulsion Test - shake the substance with ethanol for about a minute until it dissolves, then pour the solution into water.
What colours does the Emulsion Test go?
If present - lipids precipitate out of the liquid and show up as a milky emulsion. The more lipid there is, the more noticeable the milky colour will be.
If not - stays the same.
How can you test for proteins?
The Biuret Test - first, add a few drops of potassium hydroxide solution to make the solution alkaline. Then add some copper(II) sulfate solution (bright blue).
What colours does the Biuret Test go?
If present - solution turns purple.
If not - solution stays blue.
