1. 1.2 Carbohydrates Monosaccharides

2. LO: How are large molecules like carbohydrates constructed?
What is the structure of a monosaccharide?
How would you carry out the Benedict’s test for reducing sugars.

3. What are Carbohydrates made of?
Like many organic molecules carbohydrates are made up of chains of individual molecules.
Monomers – General formula CH20
Polymers – (CH20) n

4. The basic monomer unit is a sugar or saccharide.
A single monomer is called a m______________.
A pair of monosaccarides is called a d______________.
A long chain of monosaccharides is called a ____________.

5. The basic monomer unit is a sugar or saccharide.
A single monomer is called a monosaccharide.
A pair of monosaccarides is called a disaccharide.
A long chain of monosaccharides is called a polysaccharide.

6. Structure of glucose C6H12O6
Carbons form a ring, and they can make up to 4 bonds with other atoms
Glucose comes in 2 forms (isomers)– alpha or beta small difference, but major consequences when it forms polysaccharides
Each line represents a covalent bond
Learn these!

7. Key properties of monosaccharides
Other examples
Reducing sugars
Sweet tasting and soluble.
General formula (CH20)n where n = 3 to 7.
Best known is glucose a hexose (6 carbon sugar) with the formula C6H12O6.
Carbon atoms form a ring.
Draw diagram of Glucose
Sweet tasting and soluble.
General formula (CH20)n where n = 3 to 7.
Best known is glucose a hexose (6 carbon sugar) with the formula C6H12O6.
Carbon atoms form a ring.
Draw diagram of Glucose

8. Reducing sugars
All monosaccharides and some disaccharides (e.g maltose) are reducing sugars.
Reducing sugars donate electrons to (or reduce) another chemical (e.g Benedict’s reagent).

9. The Benedict’s test. A test for reducing sugars.
Benedict’s reagent is an alkaline solution of copper(II) sulphate (blue).
When a reducing sugar is heated with Benedict’s reagent it forms an insoluble red precipitate of copper(I) oxide.

10. semi-quantitative
The exact colour change will depend on the concentration of the reducing sugar.
This difference means it can be used in a semi-quantitatively to estimate the amount of reducing sugar in the sample.

11. But what % concentration of glucose causes the different colours?

12. Practical Strong glucose solution enough to turn Benedict’s red
Measuring cylinders
Distilled water
Boiling tubes
Water baths
Students to make up different known concentrations of glucose and attempt to find out what % causes the different colours

13. Splat Glucose ionic isotope monosaccharide soluble hydrolysis
polysaccharide 24
Reducing sugar
Lactose 12
covalent 3
Benedict’s reagent
monosaccharide 6
disaccharide
condensation

15. 7. (i) glycosidic; NOT glucosidic 1
(ii) 1 carbon positions 1 and 2 on glucose and fructose;
2 formation of , water / H2O , from 2 OH groups (plus separation);
3 oxygen bridge / – O – , shown; 2 max
[3]

17. 8. similar ~ allow valid similarities such as
same number , carbon / oxygen / hydrogen (atoms) / OH (groups); A hexose same formula; R similar / molecule ring / ring with O (atom) in it; correct ref CH2OH; contain C, H and O; 1 max
different ~ assume candidate is writing about fructose unless told otherwise allow valid differences such as
(fructose has) 5-membered ring / glucose has 6-membered ring; R pentose (4 C in ring v. 5C in ring / furanose v. pyranose in glucose) (in fructose) 2 CH2OH side chains / 1 CH2OH side chain in glucose; different angles between C atoms; ref alignment of H and OH groups (on carbon 3 / carbon 4); (in fructose) carbon 1 not in ring / carbon 1 in ring in glucose; 1 max
[2]

18. Describe how the concentration of glucose in a solution may be estimated by using colour comparisons.
© Pearson Education Ltd 2008
This document may have been altered from the original

19. Week 16
You could compare the reducing sugar content of orange juice and apple juice
© Pearson Education Ltd 2008
This document may have been altered from the original

20. A range of glucose solutions was made up - graph
Week 16
A range of glucose solutions was made up - graph
Glucose conc./ %
Glucose mass/mg
Absorbance
0.1
0.5
2.5
1.0
5.0
1.5
7.5
2.0
10.0
© Pearson Education Ltd 2008
This document may have been altered from the original