L4. Saccharides properties

Introduction: 

Saccharides are organic molecules consisting of C, H and O atoms. Usually the empirical formula is CnH2nOn. Are divided into three groups:

Monosaccharides: formed by a linear carbon chain, are the building blocks of oligo and polysacchariedes. They have a one functional group: cetone (C=O) or aldehyde (COH). Pentoses and hexoses can switch from acyciclic to cyclic forms called furanoses and pyranoses.

Oligosaccharides: small plymer containing between 2 and 10 monosacharides.

Polysaccharides: big polymers with more than 10 monosaccharides.

These molecules perform numerous roles in living organisms like storage if energy, structural components.  Saccharides yield 4,2 kcal/g and are abundant in fruits, sweets, honey, beans, tubers, rice...

Material:

- Test tube rack
- 10 mL pipet
- Distilled water
- 5 test tubes
- 1 dropper
- 5 spatula
- lactose
- maltose
- glucose
- sucrose
- starch
- lugol's iodine

Procedure:

From Liza's blog

1. In the first part of the experiment we're going to test some physical properities of the saccharides you have in the lab: flavour, crystal structure and colour.

test solubility

1. Clean and dry 5 test tubes and label them "G, M, L, SU, S"
2. Put 5mL of water in each test tube.
3. With the aid of spatula, put a small amount of each saccharide inside the labelled test tube and test if they are soluble or insoluble.
4. Observe if each saccharide forms a mixture called dissolution or a colloidal suspension.

Lugol's iodine test:

1.  Finally, add 2 drops of Lugol's iodine to each test tube and test if the reaction positive or negative. Lugol's is a solution of elemental iodine and potassium iodine in water that is use to test a saccharide. The reaction is positive when iodine reacts by turning from yellow to purple, dark-blue/black colour.

Qüestions: 

1. Write the empirical formula of each saccharide that you have use. Show structures of the five saccharides. Classify each one in one group: mono, oligo or polysaccharide.

Starch: (C6H1006)n  polysaccharide
Glucose: C6H1006   monosaccharide
Maltose: C12H22011 disaccharide
Sucrose: C12H22011 disaccharide
Lactose:  C12H22011 disaccharide

2. Which of the monosaccharides are aldoses and which are ketoses?

Starch: aldose
Glucose: aldose
Maltose: aldose
Sucrose: ketoses
Lactose: aldose

3. Which bond links monosaccharides?

O-glycosidic

4- Which saccaharides are sweet?  Is this property related to the structure of the molecule?

glucose, maltose, sucrose. Yes becouse monosaccharides and saccharides are sweet.

5-  Which saccharides are insoluble? Is this property related to the structure of the molecule?

Starch is insoluble. If it's a big molecule is insoluble becouse it has a high molecular weight. 

6- Wich saccharide has reacted with Lugol's iodine solution?  

Starch.

7-  Which kind of food contains starch? 

 Flour, cereal, pasta, rice, legums...

8- Caculate the energy that comes from the saccharides 

23 g x 4,2 kcal= 96,6 kcal