L5. Saccharides properties

On Monday 27th of October we did our weekly experiment in the laboratory. Saccharides are organic molecules consting of C, H and O atoms. The main objectives of this experiment were to identify the different sugars from its properties, differentiate mono and disaccharides and understand the relation between structure and some properties.

MATERIALS:
-Test tube track
-19 mL pipet
-Water
-5 test tubes
-1 dropper
-A spatula

-Lactose
-Maltose
-Glucose
-Sucrose
-Starch
-Lugol's iodine

PROCEDURE: 

In the first part of the experiment we had to test some physical properties of the saccharides we had in the lab: flavour, structure and colour. To know the flavour we put a small amount of each saccharide in our hand and tasted it. To see if they had crystals or not we observed a small amount of each saccharide on a clock glass under magnification. And to determine the colour we chose between white, transparent or creamy. 

Then we proceed to do the next part of the experiment, the test of solubility. 
1. We cleaned and dried 5 test tubes and labeled them "G, M, L, SU, S"
2. Then we put 5 mL of water in each test tube.
3. With the aid of a spatula, we put a small amount of each saccharide inside the labelled test tube and observed if they were soluble or insoluble. 

Lugol's iodine test
To each test tube we added two drops of Lugol's iodine (it acts as a starch detector) and tested if the reaction was positive or negative. Lugol's is a solution of elemental iodine (I) and potassium iodine (KI) in water that is used to test a saccharide. The reaction is positive when iodine reacts by turning from yellow to a purple, dark-blue colour. 

Results, observations and conclusions:
Lastly we completed our chart with the information. 

QUESTIONS:

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

Glucose: monosaccharide

 

C₆H₁₂O₆

Maltose: disaccharide

 C₁₂H₂₂O_{11  ·    H2O}     



                  

Sucrose: disaccharide 

C₁₂H₂₂O₁₁





Lactose: disaccharide

C₁₂H₁₂O_{11  ·}    H₂O 

Starch: polysaccharide

C₆H₁₂O₅ 








2-Which of the monosaccharides are aldoses and which are ketoses? 
Glucose: aldose // Maltose: aldose // Sucrose: ketose // Lactose: aldose // Starch: aldose

3-Which bond links monosaccharides?
O-glycosidic bond.

4-Which saccharides are sweet? Is this property related to the structure og the molecule?
Glucose, maltose and sucrose are sweet. Polysaccharides aren't sweet because of the size of the molecule, the human tongue can detect the short one- and two-molecules of the short chains. The long chains just slide on by.
 
5- Which saccharides are insoluble? Is this property related to the structure og the molecule?
 Starch because it's a big molecule (polysaccharide) with big molecular weight. 

6-Which saccharide has reacted with Lugol's iodine solution? 
 Starch.

7-Which kind of foods contain starch? 
Carbohydrates, which include pastas, breads, rice, cereals, flour, and beans. Starchy vegetables, such as potatoes, peas and corn.

8- Calculate the energy that comes from the nutrition facts label from a cereal:  
Calculate the energy that comes from the saccharides.

1 g of saccharides ----------> 4,2 Kcal
23 g of saccharides ---------> x

23 · 4,2 / 1 = 96,6 Kcal