Benedict's test

Question 1

What are the steps for benedict’s test for reducing sugars?

Answer 1

Place liquid sample in a boiling tube
Add equal volume of benedict’s solution
Heat in water bath gently for 2 mins
Brick red for reducing sugars present, blue if no reducing sugars present

Question 2

What types of sugars are reducing sugars

Answer 2

All monosaccharides and some disaccharides are reducing sugars, meaning they can donate electrons, or reduce another molecule.

Question 3

Why does the solution turn brick red when reducing sugars are present

Answer 3

The reducing sugars will react with the copper ions in benedict’s reagent, adding electrons to Cu2+, Turning it into Cu+ forming a red precipitate

Question 4

What are the steps for benedict’s test for non-reducing sugars?

Answer 4

Place liquid sample in a boiling tube
Add 2cm of HCL
Heat in water bath gently for 2 mins

Add 4cm volume of benedict’s solution
Brick red for sugars present, blue if none.

Question 5

Why is HCL added in the test for none reducing sugars

Answer 5

The sample (for example sucrose) has been hydrolysed by the acid to break down the polysaccharide into its monosaccharides (Like glucose and fructose) which are both reducing sugars

Question 6

How do you test for starch

Answer 6

Iodine test.
Mix sample with a few drops of iodine dissolved in potassium iodide solution.
If colour changes from yellow/brown to purple/black starch is present