Page 51 - Lab Manual & Project class 12

SYSTEMATIC QUALITATIVE ANALYSIS

SYSTEMATIC ANALYSIS OF ANIONS

Step - I : Preliminary Test with Dilute Sulphuric Acid

In this test the action of dilute sulphuric acid (procedure is given
below) on the salt is noted at room temperature and on warming.

2–
2–
–
Carbonate (CO ), sulphide (S ), sulphite (SO ), nitrite ( NO )
2–
3 3 2
–
and acetate (CH COO ) react with dilute sulphuric acid to evolve
3
different gases. Study of the characteristics of the gases evolved
gives information about the anions. Summary of characteristic
properties of gases is given in Table 7.1 below.
Procedure
Maxbrain Chemistry
(a) Take 0.1 g of the salt in a test tube and add 1–2 mL of
dilute sulphuric acid. Observe the change, if any, at
room temperature. If no gas is evolved, warm the
content of the test tube. If gas is evolved test it by using Fig. 7.1 : Testing a Gas
the apparatus shown in Fig.7.1 and identify the gas
evolved (See Table 7.1).

Table 7.1 : Preliminary test with dilute sulphuric acid

Inference
Observations
Gas Evolved Possible Anion

A colourless, odourless gas is evolved
with brisk effervescence, which turns CO 2 Carbonate ( CO 2– )
lime water milky. 3

Colourless gas with the smell of rotten
2–
eggs is evolved which turns lead acetate H S Sulphide (S )
2
paper black.
Colourless gas with a pungent smell, like
burning sulphur which turns acidified SO 2 2–
potassium dichromate solution green. Sulphite ( SO 3 )

Brown fumes which turn acidified
potassium iodide solution containing NO 2 Nitrite ( NO )
–
starch solution blue. 2

Colourless vapours with smell of
–
vinegar. Vapours turn blue litmus red. CH COOH vapours Acetate, (CH COO )
3
3
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24-04-2018