1.2 Carbohydrates and monosaccharides

Question 1

List the 2 most common features of monosaccharides.

Answer 1

sweet tasting

soluble

Question 2

No.of carbon atoms - name - molecular formula
3 - Triose - C₃H₆O₃
4 - Tetrose - C₄H₈O₄
5 - Pentose - C₅H₁₀O₅
6 - Hexose - C₆H₁₂O₆
7 - Heptose - C₇H₁₄O₇
What is the above table an example of?

Answer 2

Monosaccharides.

Question 3

What are carbohydrates as a monomer unit?

Answer 3

Monosaccharides

Question 4

What do pairs of monosaccharides combine to form?

Answer 4

disaccharides

Question 5

What do monosaccharides form when combined in much larger numbers?

Answer 5

polysaccharides

Question 6

Glucose + Glucose combine to form?

Answer 6

maltose

Question 7

glucose + fructose combine to form?

Answer 7

sucrose

Question 8

glucose + galactose combine to form?

Answer 8

lactose

Question 9

how are monosaccharides joined to create a polysaccharide?

Answer 9

by glycosidic bonds that were formed by condensation reactions

Question 10

When monosaccharides join what molecule is removed?

What is the reaction therefore called?

Answer 10

Water.

condensation reaction.

Question 11

How do we test if a disaccharide is a reducing sugar?

Answer 11

Benedicts solution

Question 12

How do we know if a disaccharide is non-reducing when using Benedicts solution?

Answer 12

the colour of the solution does not change when the benedicts reagent is used

Question 13

What must be done to a disaccharide in order for it to be detectable as a non-reducing sugar?

Answer 13

must be hydrolysed into its monosaccharide components through hydrolysis.

Question 14

describe how to perform a benedicts test for non-reducing sugars, and what results show a positive outcome?

Answer 14

proceed with this test only after a negative benedicts test for reducing sugars
Add dilute hydrochloric acid to sample to be tested.
heat solution to boiling point using a water bath, this is the stage at which acid hydrolysis may occur.
cool the solution under cold water and add sodium hydrocarbonate to make the solution alkaline, as much powder as needed until fizzing stops.
Use universal indicator paper to ensure that the solution is alkaline, else the benedicts reagent will not work
Add benedicts reagent to solution and heat to boiling point.
positive result indicated by a brick red solution

Question 15

How do you test for reducing sugars?

Answer 15

benedicts test

Question 16

describe how to perform a benedicts test for reducing sugars, and what results show a positive outcome?

Answer 16

Benedicts reagent mixed with sample to be tested.
Heat in a water bath or over a bunsen burner.
Positive result indicated by a change of colour to brick red from blue

Question 17

What is the principle role of carbohydrates?

Answer 17

production and storage of energy

Question 18

What is the general formula of a carbohydrate?

Answer 18

CnH₂On
where n is any number between three and eight.
Number of hydrogen atoms is always twice that of Carbon and Oxygen

Question 19

What 3 elements do all carbohydrates contain?

Answer 19

Carbon
Oxygen
hydrogen