Page 85 - Chemistry - XI

Qualitative Analysis
157 Qualitative Analysis – – Organic Organic
Compounds
Compounds

EXPERIMENT - 20

Objective
Detection of nitrogen, sulphur, chlorine, bromine and iodine in an organic compound.

Principle/Theory

In an organic compound, elements are bonded with covalent bond. Thus, it is not possible to detect them
directly by qualitative analysis. In order to test their presence in any compound, they are converted into
ionic compound by fusing them with sodium metal. During the fusion process, the elements present in
the compound are converted into water soluble sodium salts which are ionic in nature. The reactions are
given below:
Na + C + N → NaCN

2Na + S → Na S
2
Na + X → NaX (X = Cl, Br or I)
Na + S + C + N → NaSCN

Materials Required
Beaker (250 mL), China dish, test tubes, boiling tube, test tube stand, ignition tubes, test tube holder,
funnel, fi lter papers, tripod stand, wire gauze, sodium metal, CCl or CHCl , distilled water, common and
4
3
general shelf reagents

Procedure
Preparation of sodium extract or Lassaigne extract

1. Take a small amount of organic compound in a dry ignition tube and add a dry piece of sodium in it
2. Again add a small amount of organic compound into the ignition tube, so that the sodium metal is
completely covered with organic compound.
3. First heat the ignition tube gently till the sodium melts and then heat it strongly till red hot.
4. Drop the red hot ignition tube in
a china dish containing 10 mL of

distilled water and break the tube Ignition tube
into it.
5. Filter the content of China dish Water
after cooling.
6. The fi ltrate so obtained is known Organic compound China dish

as sodium extract or Lassaigne’s (a) Sodium metal (b)
extract.
Fig. 20.1: (a) Covering the sodium metal with organic compound (a) Covering the sodium metal with organic compound
(b) Dropping the ignition tube in water after ignition
(b) Dropping the ignition tube in water after ignition
83
83