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Inorganic chemistry Tests for anions and cations

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abhas
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PostSubject: Inorganic chemistry Tests for anions and cations Thu Apr 15, 2010 3:59 pm

FOR ANIONS

Take
a small amount of the substance and add a little volume of dil. HCl
(or) dil. H2SO4. Observe the reaction in cold.
Warm the contents gently and infer the reactions.

Observation

Inference

Confirmatory
Tests
Brisk effervescence in cold with evolution of
colourless and odourless gas


CO32-
(carbonate)
Pass the gas in a
test tube containing small quantity of lime water. It turns milky.
A colourless gas
with suffocating odour having smell of burning sulphur

SO32-

(sulphite)
Moisten a piece of filter paper with acidified K2Cr2O7
and put it on the mouth of the test tube. It turns green.
A colourless gas with
smell of rotten eggs

S2-
(sulphide)
Moisten a piece of filter paper with
lead acetate solution and place it on the mouth of the test tube. It
turns black.
A
light brown gas

NO2-
(nitrite)
a) Pass the evolved gas
through FeSO4 solution. It turns brown.
b) Mix the
given salt (or) mixture with a little of KI and dil. H2SO4.
Evolution of violet vapours
c) Place a piece of filter paper on
the mouth of test tube moistened with solutions of starch, KI and acetic
acid. It turns blue.
Colourless vapours with the smell of vinegar
CH3CO2-
(Acetate)
a) To the
aqueous solution of substance add neutral FeCl3 solution. A
blood red colour is formed.
b) Rub the moistered salt (or)
mixture with dry oxalic acid. Smell of vinegar is obtained.

B) Take a small amount of
the substance and add some conc. H2SO4 warm
gently, observe the changes and draw inference as follows.

Observation

Inference

Confirmatory
Tests
Colourless gas with pungent smell which fumes in air.
Add a pinch of MnO2 in the solution and a pale green gas
is evolved.

Cl-
(chloride)
a) Bring a
glass rod dipped in NH4OH on the mouth of the test tube;
white fumes are formed.
b) Bring a glass rod dipped in AgNO3
solution on the mouth of the test tube; white curdy precipitate is
formed on the rod.
c) To the substance in a dry test tube add
three times its weight of powdered K2Cr2O7 and
conc. H2SO4. Heat the contents. Red vapours are
evolved. Pass the vapour in a test tube containing NaOH solution. A
yellow precipitate appears.
Reddish brown fumes which intensify on addition of MnO2.
Vapours passed in water make it yellow

Br-
(Bromide)
a) Take
aqueous extract of the substance (or) extract with dil. HNO3
and add. AgNO3 solution. A light yellow precipitate
appears.
b) To a small amount of the substance add dil. H2SO4.
Warm and cool. Add 1 mL of CHCl3 (or) CCl4 and
then chlorine water with constant shaking. The chloroform layer
becomes orange brown.
Violet pungent fumes evolved which may condense as black
specks on the cooler parts of the test tube. The violet fumes intensify
on addition of MnO2.


I -
(Iodide)
a) Place a piece of filter paper
moistered with starch solution on the mouth of the test tube. The
paper turns blue.
b) Take aqueous extract of the substance and add
AgNO3 solution. Yellow precipitate is formed which is
insoluble in NH4OH solution.
c) To the small amount of
the substance add dil. H2SO4 and 1 mL of either
CHCl3 (or) CCl4 and then Cl2 water
with constant shaking. Chloroform layer attains violet colour.
Light brown vapours
having pungent smell. It intensifies on adding copper turnings.

NO3-
(Nitrate)
Take an
aqueous extract of the substance in a test tube and add freshly
prepared FeSO4 solution. Add conc. H2SO4
by the side of the test tube without disturbing the solution. A
brown ring is formed at the junction of two liquids.
Colourless, odourless gas which
burns with blue flame at the mouth of the test tube and turns time
water milky

C2O42-
(Oxalate)
Take the
substance, add dil. H2SO4 and heat till there
are no more effervescences. Now add MnO2 (solid) and brisk
effervescences is obtained.
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PostSubject: Re: Inorganic chemistry Tests for anions and cations Thu Apr 15, 2010 3:59 pm

ii) Flame test: It is based upon the principle
that certain volalite metallic salts, generally chlorides, when
heated in a non-luminous (oxidizing) Bunsen flame impart characteristic
colour to it. The colour is observed with naked eye and through a blue
glass (also called cobalt glass).




Cobalt nitrate test: if the residue left in the
charcoal cavity is white, it is moistened with cobalt nitrate solution
and heated in an oxidizing flame. Note the colour of the residue and
draw inference from the following table.






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PostSubject: Re: Inorganic chemistry Tests for anions and cations Thu Apr 15, 2010 4:00 pm

it is not at all necessary. but two or three readings of it with
complete conc. will gives better result on the last day before AIEEE
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PostSubject: Re: Inorganic chemistry Tests for anions and cations

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