3: Testing for carbohydrates Flashcards
What type of sugars are monosaccharides and disaccharides?
Reducing sugars
What is the chemical test for a reducing sugar?
Benedict’s test
How do you carry out a Benedict’s test?
- Place the sample in a boiling tube. If it is not in liquid form, grind it up or blend it in water.
- Add an equal volume of Benedict’s reagent.
- Heat the mixture gently in a boiling water bath for five minutes.
What is the colour change for a positive Benedict’s test for reducing sugars?
Blue to brick red
What type of sugar is sucrose?
Non-reducing sugar
How do you carry out a Benedict’s test for non-reducing sugars?
Boil the non-reducing sugar (eg sucrose) with dilute hydrochloric acid. It will then give a positive result when warmed with Benedict’s solution
What test is used for the presence of starch?
Iodine test
How do you carry out an iodine test?
Add a few drops of iodine dissolved in potassium iodide solution to the sample
What is the colour change for a positive iodine test for starch?
Yellow to black
What can reagent strips test for?
Presence of reducing sugars (most commonly glucose)
What is an advantage of using reagent strips?
With the use of a colour-coded chart, the concentration of the sugar can be determined