Testing For Reducing And Non-reducing Sugars Flashcards
What is a reducing sugar?
A sugar that can donate an electron to another molecule.
What sugars are all monosaccharides?
Reducing sugars.
What disaccharides are reducing sugars?
Maltose and lactose.
What disaccharide is a reducing sugar?
Sucrose.
What do we do at the start of each test?
Grind up the food with distilled water and filter the solid food particles.
What solution do we add to test for reducing sugars?
Benedicts solution.
How much Benedicts solution do we add?
3cm^3
What does Benedicts solution contain?
The copper ion Cu^2+
What does the copper ion Cu^2+ do in benedicts solution?
Makes the solution blue.
What do we do after we add the benedicts solution?
Place the boiling tube into a beaker of boiling water and leave for 5 mins.
What do we add the 3cm^3 of food solution to at the start?
A boiling tube.
What colour would the solution be if no reducing sugar is present?
Remains blue.
What happens if a reducing sugar is present?
An electron will be added to the copper 2+ ion to form the copper 1+ ion.
What is formed if a reducing sugar is present?
A red precipitate.
What does it mean if the solution turns green?
There is only a small amount of reducing sugar present.
What does it mean if the solution turns yellow?
There is more reducing sugar present then the green solution.
What does it mean if the solution turns orange?
There is a higher level of reducing sugar present then the green and yellow solutions.
What does it mean if the solution turns a brick red colour?
There is a lot of/most reducing sugar present.
Why do the sugars turn different colours?
There are different amount of the red precipitate mixing with the blue Benedicts solution.
Why is the Benedicta test semi-quantitative?
It only shows a narrow range of colour changes that are approximate idea of the amount of reducing sugars.
What do we need to do to test for non-reducing sugars?
Break the glycosidic bond to release the monosaccharides.
What is the first step to test for non-reducing sugars?
Carry out the Benedicts test on the unknown solution and note down any colour change.
What do we do after we carry out the benedicts test on our unknown solution?
Take a new boiling tube and add 3cm^3 of our unknown solution again.
What do we add the the unknown solution in the boiling tube?
3cm^3 of dilute hydrochloric acid.
What do we do after we add the dilute hydrochloric acid?
Gently boil the solution in a water bath for 5 mins.
What happens if a non-reducing sugar is present?
Then the acid hydrolyses the glycosidic bonds releasing the monosaccharides.
What do we add after the water bath?
3cm^3 of a dilute alkali such as sodium hydroxide.
What do we do after we add the dilute alkali?
Use pH paper to check the solution is alkaline.
Why do we add a dilute alkali?
To turn the solution alkaline as the benedicts test can’t work under acidic conditions.
What do we do last when testing for non-reducing sugars?
Carry out the Benedicts test and note down any colour change (add solution then water bath).
Why do we do a first Benedicts test in the test for non-reducing sugars?
To see if the unknown solution contains any reducing sugar.
