Salt Analysis

SEMI – MICRO QUALITATIVE ANALYSIS OF SIMPLE INORGANIC SALT
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CATIONS: Pb 2+ ,Hg 2+ ,Cu 2+ ,Cd 2+ , Ag + , Fe 2+ , Fe 3+ , Al 3+ , Zn 2+ , Mn 2+ , Co 2+ , Sr 2+ , Ba 2+ , Mg 2+ , NH4 +
ANIONS: CO3 2- , S 2- , SO3 2- , SO4 2- , NO2 - , NO3 - , Cl - , Br 2- , PO4 3- , CH3COO -
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PRELIMINARY TESTS
1. Note the state (amorphous or crystalline) and colour of salt.
2. Test the solubility of the salt in the following solutions:
i. Water (cold and hot)
ii. Dilute HCl (cold and hot)
iii. Dilute HNO3 (cold and hot)
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IDENTIFICATION OF ACID RADICALS (ANIONS)
This part is the classified into three groups:
FIRST GROUP OF ACID RADICALS
The acid radicals involved in this group are carbonate(CO3 2- ), Sulphide(S 2- ), Sulphite(SO3 2- ),
Thiosulphate(S2O3 2- ) and nitrate(NO2 - ). The group reagent is dilute hydrochloric acid.
EXPERIMENT OBSERVATION INFERENCE
Effervescence or evolution of gases 1 st group of acid radicals is present.
(a) Colourless, odourless gas turns lime water
milky The acid radical may be CO3 2- or HCO3 -(
b) Colourless with rotten eggs smell and turns
lead acetate paper black. Sulphide(S 2- ) is confirmed.
(c) Colourless gas with suffocating smell. Heat
and pass the gas through acidified K2Cr2O7
solution. The solution turns green
SO3 2- is confirmed.
(d) Colourless gas with suffocating smell with a
yellow ppt. of sulphur in the test tube. Heat and
pass the gas through acidified K2Cr2O7 solution.
The solution turns dark blackish green.
S2O3 2- is confirmed.
(e) Colourless gas followed by brown gas and it
turns starch iodide paper blue. NO2 - is confirmed.
Salt + dil. HCl
(f) Colourless gas with the smell of vinegar. The acid radical may be CH3COO --
1 -?Tests to distinguish between CO3 2- and HCO3 -
EXPERIMENT OBSERVATION INFERENCE
(a) Lime water does not turn milky. CO3 2- is confirmed. Salt + water, boil and pass the
gas through lime water (b) Lime water turns milky. HCO3 - is confirmed.
Confirmation test for Acetate
EXPERIMENT OBSERVATION INFERENCE
Salt solution + Neutral FeCl3 sol. Appearance of blood red colour. Acetate is confirmed
SECOND GROUP OF ACID RADICALS
The acid radicals involved in this group are Cl - , Br - and NO3 - . The group reagent is concentrated
sulphuric acid (H2SO4).
EXPERIMENT OBSERVATION INFERENCE
Effervescence with colourless or coloured gases 2 nd group Acid radical is
present
(a) Colourless gas with a pungent smell and gives dense
white fumes when a glass rod dipped in ammonium
hydroxide (NH4OH) is exposed.
The Acid radical may be Cl -(
b) Brown gas and the solution is not blue. The acid radical may be Br -
Salt +
Concentrated
H2SO4 and heat
if necessary.
(c) Light brown gas and brown gas with pieces of copper
turnings and the solution turns blue in the test tube. The Acid radical may be NO3 -Confirmation
test for Chloride
EXPERIMENT OBSERVATION INFERENCE
(a) Chromyl – Chloride test: Salt + few
K2Cr2O7 crystals + conc. H2SO4 and heat
Pass the vapours through the test tube
which contains NaOH solution.
To this yellow solution, add dilute
CH3COOH and lead acetate solution.
Red vapours are obtained.
The solution turns yellow.
Yellow ppt. is formed
Chloride is confirmed.
(b) Silver Nitrate test: Salt solution +
AgNO3 solution + dilute HNO3
White ppt. is formed
which is soluble in NH4OH. Chloride is confirmed.
- 2 -?Confirmation test for Bromide
EXPERIMENT OBSERVATION INFERENCE
(a) Globule Test: Aqueous solution of salt + two
drops of CCl4 + 1ml chlorine water and shake
well.
An orange-red globule is
obtained Bromide is confirmed.
(b)Silver Nitrate test: Salt solution + AgNO3
solution + dilute HNO3
A pale yellow ppt. slightly soluble
in NH4OH is obtained. Bromide is confirmed.
Confirmation test for Nitrate
EXPERIMENT OBSERVATION INFERENCE
Brown ring test: Strong solution of the substance + 2 or
3 drops of conc. H2SO4, and cool. Add freshly prepared
FeSO4 solution on the sides of the test tube.
A brown ring is formed
at the junction of two
liquids.
Nitrate is confirmed.
THIRD GROUP OF ACID RADICALS
The basic radicals involved in this group are SO4 2- and PO4 3- .
EXPERIMENT OBSERVATION INFERENCE
Test for Sulphate: Aqueous solution of salt + dilute
HCl + BaCl2 solution.
A white ppt. insoluble in dilute
HCl is obtained
Sulphate (SO4 2- ) is
confirmed.
Ammonium – Molybdate Test: 2ml of soda extract 1 +
dilute HNO3 + Ammonium Molybdate solution.
A canary yellow precipitate is
obtained.
Phosphate (PO4 3- ) is
confirmed.
1 Soda extract to be prepared if the given salt is partially soluble in water.
- 3 -?ANALYSIS OF BASIC RADICALS OR CATIONS
This is classified into 6 groups. They are mentioned as below:
GROUP RADICALS GROUP REAGENTS
I Pb 2+ ,Ag + Dilute Hydrochloric acid(HCl)
II Pb 2+ ,Hg 2+ ,Cu 2+ ,Cd 2+ Dilute HCl + H2S gas.
III Al 3+ ,Fe 2+ , Fe 3+ NH4Cl(s) + NH4OH
IV Zn 2+ ,Mn 2+ ,Co 2+ ,Ni 2+ NH4Cl(s) + NH4OH + H2S gas
V Ca 2+ ,Sr 2+ ,Ba 2+ NH4Cl(s) + NH4OH + (NH4) 2CO3
VI Mg 2+ , NH4 + -Nil-
Preparation of Original solution: A suitable solvent is found for the salt as given in the preliminary test. A
few drops are used as solution.
Test for NH4 + Radicals: This test is carried out before starting the analysis for the basic radicals.
EXPERIMENT OBSERVATION INFERENCE
(a) Salt + NaOH solution and heat it.
Expose a glass rod dipped in conc.
HCl to the gas and moist red litmus
paper.
Colourless gas with a pungent smell is
obtained.
Dense white fumes and moist red
litmus paper turns blue
NH4 + may be present in the
salt
(b) Original solution + Nesseler’s
reagent. Brown solution or ppt. is obtained NH4 + is confirmed.
FIRST GROUP OF BASIC RADICALS
The basic radicals of this group are Pb 2+ & Ag + .The group reagent is dilute HCl.
EXPERIMENT OBSERVATION INFERENCE
White ppt. is formed. May be Pb 2+ & Ag +
(a) ppt. dissolves in hot water. May be Pb 2+
(1) Original solution + Dilute HCl
Filter and add water to ppt.
and heat (b) ppt. is insoluble in water. May be Ag +
- 4 -?(a) A yellow ppt. is formed. Pb 2+ is confirmed. (2) Original solution + Potassium
Chromate solution. (b) A brick red ppt. is formed. Ag + is confirmed.
(3) Original solution + KCl sol.
ppt. obtained + water and
heat it.
A yellow ppt. soluble in hot
water, on cooling reappears as
golden yellow spangles. Pb 2+ is confirmed. The yellow ppt. is insoluble
in hot water.
SECOND GROUP OF BASIC RADICALS
The basic radicals of this group are Pb 2+ , Hg 2+ , Cu 2+ and Cd 2+ .The group reagent is Dilute HCl + H2S gas.
EXPERIMENT OBSERVATION INFERENCE
May be Pb 2+ Hg 2+ & Cu 2+ (a)A Black ppt. is observed. Original solution + Dilute HCl +
H2S gas. (b)A yellow ppt. is observed. May be Cd 2+
The identification of Pb 2+ , Hg 2+ , Cu 2+ and Cd 2+ are as follows:
EXPERIMENT OBSERVATION INFERENCE
(a) Original solution + Potassium
Chromate. A yellow ppt. is observed. Pb 2+ is confirmed.
(b)Original solution + NH4OH
A bluish white ppt. soluble in excess
of NH4OH is observed which gives
rise to a deep blue solution.
May be Cu 2+
(c) Original solution + dil. acetic
acid + potassium Ferro cyanide sol. A chocolate red ppt. is observed. Cu 2+ is confirmed.
(d) Dissolve the black ppt. in aqua
regia 2 + 1ml of distilled water,
heat & add 2 drops of SnCl2
A white ppt. is observed which turns
grey. Hg 2+ is confirmed.
(e) Original solution + dilute acetic
acid + H2S gas. A yellow ppt. is formed. Cd 2+ is confirmed.
2 Aqua regia is mixture of 3 drops of HCl + 1 drop of HNO3
- 5 -?THIRD GROUP OF BASIC RADICALS
The basic radicals of this group are Al 3+ , Fe 2+ and Fe 3+ .The group reagent is NH4Cl + NH4OH
EXPERIMENT OBSERVATION INFERENCE
May be Al 3+ (a) A white gelatinous ppt. is obtained.
(b) A dirty green ppt. is obtained May be Fe 2+
(1) Original solution +
NH4Cl(s) + NH4OH in
excess (c) A reddish brown ppt. is obtained May be Fe 3+
(a) White gelatinous ppt. soluble in excess of NaOH
is obtained which gives a colourless sol. The basic radical is Al 3+
(b) Dirty green ppt. insoluble in excess of NaOH The basic radical is Fe 2+ (2) Original solution +
NaOH solution
(c) Reddish brown ppt. insoluble in excess of NaOH The basic radical is Fe 3+
(3) Clear solution of
2(a) + solid NH4Cl and
heat
The white gelatinous ppt. reappears. Al 3+ is confirmed.
(4) Original solution +
acidified KMnO4 solution
which is added drop wise.
(a) The pink colour of KMnO4 is not discharged. Fe 3+ is confirmed.
FOURTH GROUP OF BASIC RADICALS
The basic radicals of this group are Zn 2+ , Mn 2+ , Co 2+ & Ni 2+ .The group reagent is NH4Cl + NH4OH
And H2S(g).
EXPERIMENT OBSERVATION INFERENCE
May be Zn 2+ , Mn 2+ or Co 2+ (a) a white ppt. is obtained
(1) Original solution + NH4Cl(s)
+ NH4OH in excess + H2S(g) (b) Buff or pale pink or flash coloured ppt.
soluble in dilute HCl is obtained. May be Mn 2+
(a) The white ppt. is soluble in excess of
NaOH giving a colourless solution. Zn 2+ is confirmed
(2) Original solution + NaOH
solution+. (b) The white ppt. insoluble in excess of
NaOH but turns brown. Mn 2+ is confirmed
- 6 -?A Blue colour in the alcohol
layer is obtained.
FIFTH GROUP OF BASIC RADICALS
The basic radicals of this group are Ca 2+ , Sr 2+ & Ba 2+ .The group reagent is NH4Cl(s) + NH4OH and
(NH4)2 CO3.
EXPERIMENT OBSERVATION INFERENCE
(1) Original solution + NH4Cl(s) + NH4OH in
excess + (NH4)2 CO3 solution. (a) A white ppt. is obtained. May be Ca 2+ , Sr 2+ or
Ba 2+
A yellow ppt. is obtained. May be Ba 2+ .
A thin white ppt. is obtained. May be Sr 2+ .
(2) Dissolve the white ppt. obtained in small
amounts of dilute acetic acid. Divide the
solution in three parts.
Part (1) + Potassium chromate solution.
Part (2) + Calcium Sulphate Sol. and heat.
Part (3) + Ammonium exalate solution. A white ppt. is obtained. May be Ca 2+ .
(a) Apple green coloured flame is
obtained. Ba 2+ is confirmed.
(b) Crimson red coloured flame is
obtained. Sr 2+ is confirmed.
(3)Flame tests: Make a paste of the given
salt with few drops of Conc. HCl in a watch
glass. Heat a Pt. wire in non luminous flame
till no colour is imparted to the flame. Dip
the Pt. wire in the paste and hold it in the
flame. (c) Brick red coloured flame is
obtained, Ca 2+ is confirmed.
SIXTH GROUP OF BASIC RADICALS
EXPERIMENT OBSERVATION INFERENCE
(1) Original solution + excess of NH4OH +
Ammonium Hydrogen Phosphate. A white ppt. is obtained. Mg 2+ is confirmed.
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Co 2+ is confirmed
(3) Dissolve the 1(a) in aqua regia, evaporate to
Dryness, add 1ml of distilled water and divide
the resultant product into two parts.
Part (1) + 1 ml of amyl alcohol + 100 mg of solid
NH4SCN and stir it.
Part (2) + 5 drops of dimethyl glyaxime reagent +
NH4OH. A pink ppt. is obtained. Ni 2+ is confirmed.
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