1.2 carbohydrates and monosaccharides

Question 1

how are carbohydrates constructed?

Answer 1

• Carbohydrates contain carbon, hydrogen and oxygen atoms.

- The basic monomer unit for a carbohydrate is a monosaccharide.

Question 2

Describe the structure of monosaccharides.

Answer 2

• soluble
• general formula: (CH2O)n
• all monosaccharides are reducing sugars
• the atoms can be arranged in different ways, forming isomers, for example glucose has two isomers; alpha and beta glucose.

Question 3

name 3 monosaccharides

Answer 3

Glucose, galactose, fructose

Question 4

Describe the difference in structure between alpha and beta glucose.

Answer 4

Alpha glucose has the right hand hydroxyl group below the hydrogen.
Beta glucose has the right hand hydroxyl group above the hydrogen.

Question 5

What is the test for reducing sugars?

Answer 5

1) Add 2cm3 of the food sample to a test tube. make sure it is in liquid form.
2) add an equal volume of benedict’s reagent.
3) heat the mixture in gently boiling water for five minutes.

Question 6

what are the results of the test for reducing sugars?

Answer 6

none: blue solution
very low: green solution
low: yellow solution
medium: orange solution
high: red solution

Question 7

what is a reducing sugar?

Answer 7

A sugar that can donate electrons to another chemical (Eg: benedict’s reagent)

Question 8

What are the special features of carbon?

Answer 8

• They readily form bonds with other carbon atoms allowing a sequence to build up.
• This creates a backbone to which other atoms can attach.

Question 9

Why does Benedict’s solution change colour in the test for reducing sugars?

Answer 9

the blue copper(II) sulfate in the reagent is reduced by the reducing sugar into copper(I) oxide which produces a red colour.