Page 60 - Lab Manual & Project class 12

LABORATORY MANUAL CHEMISTRY
(b) Acidify the sodium carbonate extract of the salt with dil. HNO .
3
Add silver nitrate (AgNO ) solution and shake the test tube. A pale
3
yellow precipitate is obtained which dissolves in ammonium hydroxide
with difficulty.
NaBr + AgNO NaNO + AgBr
3 3
Silver bromide
Pale yellow precipitate

–
3. Test for Iodide ion ( I )
(a) If on heating the salt with conc. H SO , deep violet vapours with a
2
4
pungent smell are evolved. These turns starch paper blue and a violet
sublimate is formed on the sides of the test tube, it indicates the presence
–
of I ions. Some HI, sulphur dioxide, hydrogen sulphide, and sulphur
are also formed due to the following reactions.
Iodine, 2NaI + 2H SO Na SO + SO + 2H O + I
harmful by 2 4 2 4 2 2 2
inhalation
and contact I + Starch Blue colour
2
with skin solution
Chlorine, NaI + H SO 4 NaHSO + HI
4
2
toxic by
inhalation 2HI + H SO 2H O + I + SO
2 4 2 2 2
6NaI + 4H SO 3I + 4H O +S + 3Na SO
Chloroform, Maxbrain Chemistry 2 4
4
2
2
2
harmful and
toxic by 8NaI + 5 H SO 4 4I + H S + 4Na SO + 4H O
2
2
2
2
4
2
inhalation
On adding MnO to the reaction mixture, the violet vapours become
2
dense.
2NaI + MnO + 2H SO I + MnSO + Na SO + 2H O
2 2 4 2 4 2 4 2
(b) Add 1 mL of CHCl or CCl and chlorine water in excess to the salt
3
4
solution in water or sodium carbonate extract neutralised with dil.HCl
and shake the test tube vigorously. Presence of violet colouration in the
organic layer confirms the presence of iodide ions.
2NaI + Cl 2NaCl + I
2 2
Iodine dissolves in the organic solvent and the solution becomes violet.
(c) Acidify sodium carbonate extract of the salt with dil.HNO and add
3
AgNO solution. Appearance of a yellow precipitate insoluble in excess
3
of NH OH confirms the presence of iodide ions.
4
NaI + AgNO AgI + NaNO
3 3
silver iodide
(Yellow precipitate)
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24-04-2018