Page 54 - Lab Manual & Project class 12

LABORATORY MANUAL CHEMISTRY
colouration due to the formation of complex compound Na [Fe(CN) NOS]
5
4
confirms the presence of sulphide ion in the salt.
Na S + Na [Fe(CN) NO] Na [Fe(CN) NOS]
2
5
5
2
4
Sodium nitroprusside Complex of Purple colour
2–
3. Test for Sulphite ion [SO ]
3
(a) On treating sulphite with warm dil. H SO , SO gas is evolved which is
4
2
2
suffocating with the smell of burning sulphur.
Na SO + H SO Na SO + H O + SO
2 3 2 4 2 4 2 2
The gas turns potassium dichromate paper acidified with dil. H SO , green.
Barium 2 4
compounds K Cr O + H SO + 3SO K SO + Cr (SO ) + H O
2 2 7 2 4 2 2 4 2 4 3 2
Maxbrain Chemistry
Chromium
sulphate (green)
Potassium (b) An aqueous solution or sodium carbonate extract of the salt produces a
permanganate white precipitate of barium sulphite on addition of barium chloride solution.
Na SO + BaCl 2NaCl + BaSO
2 3 2 3
This precipitate gives following tests.
(i) This precipitate on treatment with dilute HCl, dissolves due to
decomposition of sulphite by dilute HCl. Evolved SO gas can be tested.
2
BaSO + 2HCl BaCl + H O + SO
3 2 2 2
(ii) Precipitate of sulphite decolourises acidified potassium permanganate
solution.

BaSO + H SO 4 BaSO + H O + SO 2
2
4
2
3
2KMnO + 3H SO K SO + 2MnSO + 3H O + 5 [O]
4 2 4 2 4 4 2
SO + H O + [O] H SO
2 2 2 4
–
4. Test for Nitrite ion [NO ]
2
(a) On treating a solid nitrite with dil. H SO andwarming,reddish brown
2
4
fumes of NO gas are evolved. Addition of potassium iodide solution to
2
the salt solution followed by freshly prepared starch solution and
acidification with acetic acid produces blue colour. Alternatively, a filter
paper moistened with potassium iodide and starch solution and a few
drops of acetic acid turns blue on exposure to the gas due to the
interaction of liberated iodine with starch.
(i) 2NaNO + H SO Na SO + 2HNO
2 2 4 2 4 2
3HNO HNO + 2NO + H O
2 3 2
2NO + O 2NO
2 2
Brown gas
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24-04-2018