Page 58 - Lab Manual & Project class 12

LABORATORY MANUAL CHEMISTRY

–
*Nitrate ( NO ) Take 1 mL of salt solution in water in a test tube. Add 2 mL
3
conc. of H SO and mix thoroughly. Cool the mixture under
2
4
the tap. Add freshly prepared ferrous sulphate along the
sides of the test tube without shaking. A dark brown ring is
formed at the junction of the two solutions.
Oxalate ( C O 2– ) (a) Take 1 mL of water extract or sodium carbonate
2 4
extract acidified with acetic acid and add calcium
chloride solution. A white precipitate insoluble in
ammonium oxalate and oxalic acid solution but
soluble in dilute hydrochloric acid and dilute nitric
acid is formed.
(b) Take the precipitate from test (a) and dissolve it in
dilute H SO . Add very dilute solution of KMnO and
4
2
4
warm. Colour of KMnO solution is discharged. Pass
4
the gas coming out through lime water. The lime water
turns milky.
Chemistry of Confirmatory Tests
–
1. Test for Chloride ion [Cl ]
(a) If on treatment with warm conc. H SO the salt gives a colourless gas
2
4
with pungent smell or and if the gas which gives dense white fumes
–
with ammonia solution, then the salt may contain Cl ions and the
following reaction occurs.
NaCl + H SO NaHSO + HCl
4
Manganese 2 4 Sodium Hydrogen chloride
dioxide Maxbrain Chemistry
hydrogen sulphate Colourless gas
HCl + NH NH Cl
3 4
Ammonium chloride
Silver nitrate
White fumes
(b) If a salt gives effervescence on heating with conc. H SO and MnO and
2
4
2
a light greenish yellow pungent gas is evolved, this indicates the presence
–
of Cl ions.
MnO + 2NaCl + 2H SO Na SO + MnSO + 2H O + Cl
2 2 4 2 4 4 2 2
(c) Salt solution acidified with dilute HNO on addition of silver nitrate
3
solution gives a curdy white precipitate soluble in ammonium hydroxide
–
solution. This indicates the presence of Cl ions in the salt.
NaCl + AgNO 3 NaNO + Ag Cl
3
Silver chloride
(White precipitate)
AgCl + 2NH OH [Ag(NH ) ]Cl + 2H O
4 3 2 2
Diammine silver (I)
chloride

* This test can also be performed by adding first ferrous sulphate solution and then conc. H SO .
2 4
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24-04-2018