Tests for the presence of substances Flashcards
What is the method for testing for a non-reducing sugar?
- Add HCl, boil and cool the solution
- Add sodium hydrogencarbonate
- Add Benedict’s reagent
What is observed in the Benedict’s test for a reducing sugar if a reducing sugar is not present?
Solution remains blue
What is observed in the Benedict’s test for a reducing sugar if a reducing sugar is present?
A red precipitate is formed
Why is acid used in the Benedict’s test for a non-reducing sugar?
It hydrolyses the glycosidic bond
Why is sodium hydrogencarbonate used in Benedict’s test for a non-reducing sugar?
Neutralises the solution as Benedict’s reagent doesn’t work in acidic conditions
What is the test used for a reducing sugar?
Add an equal amount of benedict’s solution
Place in a water bath for 3 minutes
What is observed in the Benedict’s test for a non-reducing sugar if a non-reducing sugar is present?
Brick red precipitate formed
How can starch be tested for?
Adding potassium iodide solution
What is observed in a positive starch test?
Black/dark purple solution is formed
Describe the method for testing for the presence of proteins
Add Biuret’s reagent down the side of the test tube
Shake
What is observed in a positive test for proteins?
Purple solution is formed
Describe the method for testing for lipids
- Add ethanol and shake
- Add this solution to water and shake
What is observed in a positive test for lipids?
A white emulsion is formed