Testing for sugars Flashcards
Which carbohydrates are known as reducing sugars
- Monosaccharides such as - glucose/fructose and galactose and Disaccharides such as Maltose, and Lactose are all known as reducing sugars
What is the name given to the test for reducing sugars
Benedicts test
What does Benedicts test involve
Equal volume of Benedicts reagent and the solution being tested are heated to at least 70 degrees If a reducing sugar such as glucose is present, the solution will turn from blue, to green, to yellow, to orange and finally red.
Give the name of a non reducing sugar
Disaccharide - Sucrose
Which sugars are reducing sugars and which sugars are not?
All monosaccharides and some disaccharides e.g. maltose are reducing sugars
What makes Monosaccharides and Disaccharides a reducing sugar
They both have Carbonyl groups which can be oxydised to form carboxylic acids.
(NB: During an oxidation reaction oxygen is added)
This means that they can reduce other compounds such as Benedicts reagent, when heated, producing preciptate.
What is benedicts test used for
To estimate the amount of reducing sugar present in a solution.
What determins the colour of the precipate remaining from the reducing sugar
The concentration of the reducing sugar
What are the 5 colours used to measure a reducing sugar in a solution in benedicts test
- Blue
- Green
- Yellow
- Brown
- Red
Which colour in benedicts test = no reducing sugars
Blue
What is the colour in benedicts test which reflects high levels of reducing sugars
Red
What is the flow of colours from zero which illustrate increasing levels of reducing sugars
- Blue
- Yellow
- Green
- Brown
- Red
What other tool might you use to test for glucose
A reagent strip
Which disaccharides give a negative benedicts test
Sucrose
What might you do to change this
Break the Sucrose down into its Monosaccharide parts by heating with hydrochloric acid. The individual sugars will then show up positive
