Page 63 - Lab Manual & Project class 12

SYSTEMATIC QUALITATIVE ANALYSIS
Chemistry of Confirmatory Tests

2–
1. Test of Sulphate ions [SO ]
4
(a) Aqueous solution or sodium carbonate extract of the salt acidified with
acetic acid on addition of barium chloride gives a white precipitate of
barium sulphate insoluble in conc. HCl or conc. HNO .
3
Na SO + BaCl 2 BaSO + 2NaCl
4
4
2
Barium sulphate
(White precipitate)
(b) Sulphate ions give white precipitate of lead sulphate when aqueous
solution or sodium carbonate extract neutralised with acetic acid is
Maxbrain Chemistry
treated with lead acetate solution.

Na SO + (CH COO) Pb PbSO + 2CH COONa
2 4 3 2 4 3
Lead sulphate
(White precipitate)

3–
2. Test for Phosphate ion [PO ]
4
(a) Add conc. HNO and ammonium molybdate solution to the test solution
3
containing phosphate ions and boil. A yellow colouration in solution
or a canary yellow precipitate of ammonium-phosphomolybdate,
(NH ) [P (Mo O ) ] is formed. Each oxygen of phosphate has been
10 4
4 3
3
replaced by Mo O group.
10
3
Na HPO + 12 (NH ) MoO + 23 HNO 3 (NH ) [P (Mo O ) ] + 2NaNO + 21NH NO + 12H O
2
4
10 4
3
4 3
2
3
4
4 2
4
3
Canary yellow
precipitate
SYSTEMATIC ANALYSIS OF CATIONS
The tests for cations may be carried out according to the following scheme.
Step - I : Preliminary Examination of the Salt for Identification of Cation

1. Colour Test
Observe the colour of the salt carefully, which may provide useful information
about the cations. Table 7.6 gives the characteristic colours of the salts of some
cations.

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24-04-2018