Carbohydrates are organic compounds made of carbon, hydrogen, and oxygen that serve important roles in living systems. They are divided into monosaccharides, disaccharides, and polysaccharides based on their structure. The Molisch test is a general and sensitive test used to detect the presence of all carbohydrates using concentrated sulfuric acid and alpha-naphthol to produce a purple color.

1. CARBOHYDRATES

2. Carbohydrates
• Carbohydrates are compounds composed of
carbon, hydrogen and oxygen containing an
aldehyde or ketone functional group and
many alcohol groups, and can also be called
polyhydroxy aldehydes or polyhydroxy
ketones.

3. Usually combine the carbonyl classification
and the number classification together.
C
O
H
C OH
H
CH2OH
glyceraldehyde
aldotriose
C
O
H
C OH
H
C H
HO
C OH
H
C OH
H
CH2OH
CH2OH
C O
C H
HO
C OH
H
C OH
H
CH2OH
glucose fructose
aldohexose ketohexose

4. Background
• A carbohydrate is an organic compound with
the general formula Cn(H2O)n, that is, consists
only of carbon, hydrogen and oxygen, with the
last two in the 2:1 atom ratio.
• Carbohydrates make up the bulk of organic
substances on earth and perform numerous
roles in living systems.
• The carbohydrates (saccharides) are divided into
three categories:
• Monosaccharides, disaccharides, and
polysaccharides.

5. Types of Carbohydrates
Monosaccharides
• Found in fruits and dairy products
• Easily digested by the body
Disaccharides
•Found in fruits
•Composed of two simple sugars
Polysaccharides
•Commonly found in vegetables (cellulose), whole grain
breads
•It takes longer for the body to digest
5

6. General Test
for
Carbohydrates

7. Chemical Tests for Carbohydrates
• 1) Molisch Test
• 2) Seliwanoff Test
• 3) Bial Test
• 4) Fehling's Test
• 5) Benedict's test
• 6) Barfoed's Test

8. 1) Molisch’s Test:
• Molisch’s Test is a sensitive chemical test for all
carbohydrates based on the dehydration of the
carbohydrate by H2SO4 to produce an aldehyde
(either furfural or a derivative), which then
condenses with the phenolic structure resulting
in a red or purple-colored compound.

12. 1. Tilt the test tube at a 45 degree angle and carefully add 40
drops of concentrated sulfuric acid by slowly dripping
it down the side of the test tube. Do NOT mix the solutions.
The sulfuric acid should form a layer beneath the
carbohydrate layer.
2. Set the test tubes carefully in the rack
and observe for evidence of a reaction
over the next 15-20 minutes.
Record your results

14. Thank you

15. Exp. 1 Molisch Test
• It is the general test for all carbohydrates.
• Monosaccharides give a rapid positive test.
Disaccharides and polysaccharides react
slower.

16. Exp. 1 Molisch Test
• The Molisch reagent dehydrates
pentoses to form furfural.
• dehydrates hexoses to form 5-
hydroxymethyl furfural.
• The furfurals further react with -
naphthol present in the test
reagent to produce a purple
product.

17. Exp. 1 Molisch Test
■ Method:
• 1ml test solution + 2 drops of α-naphthol
• mix well
• add conc. H2SO4 down the side of the tube to form
the ring at the interface of the two layers.
- ve + ve