INORGANIC MATERIAL

CHEMISTRY
Prepared by:
Asad Noman and Muhammad Awais

SUBMITTED TO:

Dr. Farhat Nosheen

BS CHEMISTRY
VI SEMESTER
UNIVERSITY OF EDUCATION JAUHARABAD
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Experiment #01
Estimation of Anions in the Mixture:
Introduction:
Solubility of a salt in water and the pH of aqueous solutions give important information about the
nature of ions present in the salt. If a solution of the salt is acidic or basic in nature, this means that
it is being hydrolyzed in water. If the solution is basic in nature, then salt may be some carbonate
or sulphide etc. If the solution shows acidic nature, then it may be an acid salt or salt of weak base
and strong acid. In this case it is best to neutralize the solution with sodium carbonate before testing
it for anions. Gases evolved in the preliminary tests with dil. H2SO4/dil. HCl and conc. H2SO4
also give good indication about the presence of acid radicals (See Tables 7.1). Preliminary tests
should always be performed before starting the confirmatory tests for the ions.
Two basic principles of great use in the analysis are:
(i) the Solubility product,
(ii) the Common ion effect.
When ionic product of a salt exceeds its solubility product, precipitation takes
place. Ionic product of salt is controlled by making use of common ion effect
which you have studied in the textbook of chemistry.

Material Required:
• Boiling tube: As per need
• Test tubes: As per requirement
• Measuring cylinder: One
• Test tube stand: One
• Test tube holder: One
• Delivery tube: One
• Corks: As per need
• Filter paper: As per need
• Reagents: As per need

Step - I: Preliminary Test with Dilute Sulphuric Acid:

In this test the action of dilute sulphuric acid (procedure is given below) on the salt is noted at
room temperature and on warming. Carbonate, sulphide, sulphite, nitrite and acetate react with
dilute sulphuric acid to evolve different gases. Study of the characteristics of the gases evolved
gives information about the anions. Summary of characteristic properties of gases is given in Table
7.1 below.
Procedure:
(a) Take 0.1 g of the salt in a test tube and add 1–2 mL of dilute sulphuric acid. Observe the change,
if any, at room temperature. If no gas is evolved, warm the content of the test tube. If gas is evolved,
identify the gas evolved (See Table 7.1).
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Table 7.1: Preliminary test with dilute sulphuric acid

Observation Gas Evolved Possible ion

A colorless, odorless gas is evolved with CO2 Carbonate CO32-

brisk effervescence, which turns lime water
milky.

Colorless gas with the smell of rotten eggs is H2S Sulphide S2-
evolved which turns lead acetate paper black.

Colorless gas with a pungent smell, like SO2 Sulphite SO32-

burning Sulphur which turns acidified
potassium dichromate solution green.

Brown fumes which turn acidified potassium NO2 Nitrite NO2-

iodide solution containing starch solution
blue.

Colorless vapors with smell of vinegar. CH2COOH vapors Acetate CH3COO-

Vapors turn blue litmus red.

Confirmatory tests for CO3 2- S2-, SO32- , NO2 and CH3COO-:

Confirmatory (wet) tests for anions are performed by using water extract when salt is soluble in
water and by using sodium carbonate extract when salt is insoluble in water. Confirmation of CO3
is done by using aqueous solution of the salt or by using solid salt as such because sodium
carbonate extract contains carbonate ions. Water extract is made by dissolving salt in water.
Preparation of sodium carbonate extract is given below.
Preparation of sodium carbonate extract:
Take 1 g of salt in a porcelain dish or boiling tube. Mix about 3 g of solid sodium carbonate and
add 15 mL of distilled water to it. Stir and boil the content for about 10 minutes. Cool, filter and
collect the filtrate in a test tube and label it as sodium carbonate extract.

Confirmatory tests for acid radicals, which react with dilute sulphuric acid
are given below
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1. Test for Carbonate ion [CO32-:

Procedure:
Take 0.1 g of salt in a test tube, add dilute sulphuric acid. CO2 gas is evolved with brisk
effervescence which turns lime water milky. On passing the gas for some more time, milkiness
disappears.

If there is effervescence with the evolution of a colorless and odorless gas on adding dil. H2SO4
to the solid salt, this indicates the presence of carbonate ion. The gas turns lime water milky due
to the formation of CaCO3.
Na2CO3 + H2SO4 Na2SO4 + H2O +CO2
Ca(OH)2 + CO2 CaCO3 + H2O
If CO2 gas is passed in excess through lime water, the milkiness produced disappears due to the
formation of calcium hydrogen carbonate which is soluble in water.
CaCO3 + CO2 + H2O Ca (HCO3)2
2. Test for Sulphide ion [S2–]:

Procedure:
Take 1 mL of water extract and make it alkaline by adding ammonium hydroxide or sodium
carbonate extract. Add a drop of sodium nitroprusside solution. Purple or violet coloration appears.
1. With warm dilute H2SO4 a sulphide gives hydrogen sulphide gas which smells like rotten
eggs. A piece of filter paper dipped in lead acetate solution turns black on exposure to the
gas due to the formation of lead sulphide which is black in color.
Na2S + H2SO4 Na2SO4 + H2S
(CH3COO)2Pb + H2S PbS + 2CH3COOH
Lead sulphide Black precipitate.

2. If the salt is soluble in water, take the solution of salt in water make it alkaline with
ammonium hydroxide and add sodium nitroprusside solution. If it is insoluble in water
take sodium carbonate extract and add a few drops of sodium nitroprusside solution.
Purple or violet coloration due to the formation of complex compound Na4[Fe(CN)5NOS]
confirms the presence of sulphide ion in the salt.
Na2S + Na2 [Fe(CN)5NO] Na4 [Fe(CN)5NOS]
Sodium nitroprusside Complex of Purple color

3. Test for Nitrite ion [NO2-:

Procedure:
1. Take 1 mL of water extract in a test tube. Add a few drops of potassium iodide solution
and a few drops of starch solution, acidify with acetic acid. Blue color appears.
2. Acidify 1 mL of water extract with acetic acid. Add 2-3 drops of sulphanilic acid solution
followed by 2-3 drops of 1-naphthylamine reagent. Appearance of red color indicates the
presence of nitrite ion.
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3. On treating a solid nitrite with dil. H2SO4 and warming, reddish brown fumes of NO2 gas
are evolved. Addition of potassium iodide solution to 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) 2NaNO2 + H2SO4 Na2SO4 + 2HNO2
3HNO2 HNO3 + 2NO + H2O
2NO + O2 2NO2 Brown gas
(ii) NO2 + CH3COOH HNO2 + CH3COO–
2HNO2 + 2KI + 2CH3COOH 2CH3 COOK + 2H2O + 2NO + I2
I2 + Starch Blue complex

4. Sulphanilic acid — 1-naphthylamine reagent test (Griss-Ilosvay test) On adding

sulphanilic acid and 1-naphthylamine reagent to the water extract or acidified with acetic
acid, sulphanilic acid is diazotised in the reaction by nitrous acid formed. Diazotised acid
couples with 1-naphthylamine to form a red azo-dye.

NO2 + CH3COOH HNO2 + CH3COO

4. Test for Sulphite ion [SO3-2]:

Procedure:
1. Take 1 mL of water extract or sodium carbonate extract in a test tube and add barium
chloride solution. A white precipitate is formed which dissolves in dilute hydrochloric acid
and sulphur dioxide gas is also evolved.
2. Take the precipitate of step (a) in a test tube and add a few drops of potassium
permanganate solution acidified with dil. H2SO4. Colour of potassium permanganate
solution gets discharged.

3. On treating sulphite with warm dil. H2SO4, SO2 gas is evolved which is suffocating with
the smell of burning sulphur.
Na2SO3 + H2SO4 Na2SO4 + H2O + SO2
The gas turns potassium dichromate paper acidified with dil. H2SO4, green.
K2Cr2O7 + H2SO4 + 3SO2 K2SO4 + Cr2 (SO4)3 + H2O
Chromium sulphate (green)

4. An aqueous solution or sodium carbonate extract of the salt produces a white precipitate of
barium sulphite on addition of barium chloride solution.
Na2SO3 + BaCl2 2NaCl + BaSO3
This precipitate gives following tests.
 This precipitate on treatment with dilute HCl, dissolves due to decomposition of sulphite
by dilute HCl. Evolved SO2 gas can be tested.
BaSO3 + 2HCl BaCl2 + H2O + SO2
 Precipitate of sulphite decolourises acidified potassium permanganate solution.
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BaSO3 + H2SO4 BaSO4 + H2O + SO2

2KMnO4 + 3H2SO4 K2SO4 + 2MnSO4 + 3H2O + 5 [O]
SO2 + H2O + [O] H2SO4

5. Test for Acetate ion [CH3COO–]:

Procedure:
1. Take 0.1 g of salt in a china dish. Add 1 mL of ethanol and 0.2 mL conc.
H2SO4 and heat. Fruity odour confirms the presence of acetate ion.
2. Take 0.1 g of salt in a test tube, add 1-2 mL distilled water, shake well
filter if necessary. Add 1 to 2 mL Neutral ferric chloride solution to the
filtrate. Deep red colour appears which disappears on boiling and a
brown-red precipitate is formed.

3. If the salt smells like vinegar on treatment with dil. H2SO4, this indicates
the presence of acetate ions. Take 0.1 g of salt in a china dish and add 1
mL of ethanol. Then add about 0.2 mL of conc. H2SO4 and heat. Fruity
odour of ethyl acetate indicates the presence of CH3COO– ion.
2 CH3COONa + H2SO4 Na2SO4 + 2 CH3COOH
CH3COOH + C2H5OH CH3COOC2H5 + H2O
Ethylacetate (Fruity odour)

4. Acetate gives deep red colour on reaction with neutral ferric chloride
solution due to the formation of complex ion which decomposes on
heating to give Iron (III) dihydroxyacetate as brown red precipitate.
6 CH3COO– + 3Fe3+ + 2H2O [Fe3(OH)2 (CH3COO)6]+ +
2H+
[Fe3(OH)2 (CH3COO)6]+ 4H2O 3[Fe (OH)2 (CH3COO)] + 3CH3COOH
Iron(III)dihydroxyacetate (Brown-red precipitate).

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