2.3 Carbohydrates

Question 1

Learning outcomes

Answer 1

-Describe the structure of a variety of
monosaccharides.
-Explain how monosaccharides form to make Disaccharides.

Question 2

Monosaccharides

Answer 2

• Simplest_ “sigle sugars”
• All have 6 carbon atoms_“hexose” sugar
• All are ‘Isomers’ of glucose.
• Same number o C atoms as O atoms.(eg. C6H12O6)
• Have a general formula and (CH2O)n
• White crystalline solids
• Dissolves in water to form sweet tasting solution.(Soluble)

Question 3

Reactions

Answer 3

-Monosaccharide -> polysaccharide

_This done using a condensation reaction.

Question 4

Key start

Answer 4

Study the different disaccharides kn the slide show.

Question 5

Benedict solution test_testing for reducing sugars

Answer 5

Step 1: Place 2 ml of the substance in a boiling tube (substance must be in liquid form).
Step 2: Add 10 drops of Benedict’s solution.
Step 3: Place in a boiling water bath for 3-5 minutes.

Question 6

Benedict solution results

Answer 6

Blue solution → no reducing sugar.
Green/yellow precipitate → traces of reducing sugar.
Orange/red precipitate → moderate amounts of reducing sugar.
Brick red precipitate → large amount of reducing sugar.

Question 7

Test for non-reducing sugars

Answer 7

Step 1: Boil in dilute HCl (to hydrolyse the non-reducing sugar).
Step 2: Neutralise the solution by adding sodium hydrogen carbonate.
Step 3: Repeat the Benedict’s test.