Lesson 7.5 - Testing for Carbohydrates Flashcards
Reducing sugars examples?
Monosaccharides and some disaccharides (e.g. maltose and lactose)
Meaning of reducing sugars?
They can donate electrons, or reduce another chemical / molecule.
Reducing meaning in chemistry?
Reaction involving the gain of electrons
What is Benedicts reagent?
alkaline solution of Copper (II) sulfate.
What is used in test for reducing sugars?
Benedicts reagent
Test for reducing sugars:
- Place sample to be tested in a boiling tube. If it is not a liquid, grind it up with water or blend it.
- Add equal volume of benedicts reagent.
- Heat the mixture gently in a boiling water bath for 5 minutes.
Colour change of Benedicts reagent?
Blue –> Brick-red
Why is there a colour change in the test for reducing sugars?
- The reducing sugars react with the copper (II) ions.
- Results in the addition of electrons to the blue Cu+2 ions. This reduces them to brick-red Cu+ ions.
What happens when reducing sugar is mixed with benedicts solution and warms?
Brick-red precipitate forms
How is the test for reducing sugars qualitative?
More reducing sugars present = more Cu+
Colour of solution is a mix of brick-red Cu+ ions and blue Cu+2 ions.
Colour changes of reducing sugars:
High: Brick-red
Medium: Orange / Yellow / Amber
Low: Green
None: Blue
Iodine test:
Test for starch
How does the iodine test work for starch?
Few drops of iodine dissolved in potassium iodine solution and are mixed with the solution.
If solution colour changes from yellow/brown to black/blue then starch is present.
Reagent strips?
Manufactured tests to test for reducing sugars. Most commonly glucose.
Advantage of reagent strips?
Colour-coded chart to determine the concentration of reducing sugars.
