16
Principles Related to
Practical Chemistry
Experimental (practical) chemistry involves the study of concerned material IN THIS CHAPTER ....
under specific experimental conditions. It can be divided into two branches :
synthetic chemistry and analytical chemistry. Qualitative Analysis of Organic
Compounds
Qualitative Analysis of Organic Compounds Preparation of Inorganic
Compounds
Two major steps involved in the characterisation of an organic compound are
(i) Element detection (For it see chapter 12 purification and characterisation Preparation of Organic
of organic compounds) (ii) Detection of functional group. Compounds
Practical Inorganic Chemistry
Detection of Functional Groups
Element detection shows the presence or absence of different elements. On
the basis of element present, the test of corresponding functional group is
performed.
Tests for different functional groups are given below
Tests for Carboxylic (— COOH) Group
(i) Litmus paper test Dip blue litmus paper in the aqueous solution or
suspension of the compound. It turns red.
(ii) Sodium bicarbonate test In a test tube, take a little quantity of the
compound and then, add a saturated solution of sodium bicarbonate.
Formation of brisk effervescence due to the formation of CO2 shows the
presence of ¾ COOH group.
–+
®
COOH + NaHCO3 COONa + H2O + CO2
Benzoic acid Sodium benzoate
,1188 JEE Main Chemistry
(iii) Ester formation Heat a small quantity of organic Tests for Phenolic (Ph¾ OH) Group
compound with ethyl alcohol and a little conc. H 2SO4 ×
Cool the solution and pour in a tube containing (i) Ferric chloride test Take few drops of ferric
water. A fruity smell, due to formation of an ester, chloride solution and add 2-3 drops of the compound
indicates the presence of carboxylic group. to it. Appearance green, blue or violet colour shows
the presence of phenol.
Conc. H2SO 4
R ¾ COOH + C2H5 OH ¾¾¾¾¾® RCOOC2H5 + H2O 6C6 H5 OH + FeCl3 ¾® 3H+ + [Fe(OC6 H5 )6 ]3 - + 3HCl
D
Carboxylic acid Ethanol Ester Phenol Ferric Violet
(fruity smell) chloride
This test is also given by enols.
Tests for Alcoholic (—OH) Group
(ii) Liebermann’s nitroso reaction Take little amount
(i) Sodium test In a test tube, take some organic of compound and add 1mL of conc. H 2SO4 to it. Shake
compound and add a thin piece of sodium metal to it. and warm the test tube. Cool and then add crystals of
A brisk effervescence due to the formation of sodium nitrite (NaNO2 ).
hydrogen gas takes place.
- + A deep green to blue solution is formed which turns
2ROH + 2Na ¾® 2R ONa + H 2 red on dilution. The red aqueous solution becomes
(ii) Ester test Heat the given compound with acetic acid again deep green or blue if made alkaline with
in the presence of sulphuric acid. A fragrance of NaOH. It shows the presence of phenol.
fruity smell indicates the formation of ester. C6H5OH, H2SO4
HNO2
Conc. H 2SO4 —OH HO— —NO
ROH + CH3 COOH CH3 COOR + H2O
Acetic acid Ester Phenol
(fruity smell) NaOH
O N OH
Alcohols give crystalline esters with 3,5-dinitrobenzoyl
chloride. These esters have sharp melting points and
Indophenol ion
can be used for testing a given alcohol.
–
O NO2 O NO2
O N O
ROH + Cl—C— R—O—C— + HCl
Indophenol (blue)
NO2 NO2
3, 5-dinitrobenzoyl Crystalline ester
chloride Note Nitrophenol do not respond to FeCl3 test as well as
Liebermann’s nitroso reaction.
(iii) Ceric ammonium nitrate test To small amount of
(iii) Phthalein test Phenol on heating with phthalic acid
organic compound or its aqueous solution, add a few
in presence of conc. H 2SO4 gives colourless compound
drops of ceric ammonium nitrate. A red colour
called phenolphthalein, which appear pink coloured
indicates the presence of alcoholic hydroxy group. compound in alkaline medium.
2ROH + (NH4 )2 Ce(NO3 )6 ¾® Ce(NO3 )4 × (ROH)2 O
Alcohol Ceric ammonium O
Red colour
nitrate
+ 2NH4 NO3 C
—C—OH H2SO4, D 2C6H5OH, D
This test is useful when the compound contains less O
—C—OH
than 10 C-atoms. C
(iv) Lucas test This test is used to distinguish between O
primary, secondary and tertiary alcohols. Phthalic acid O
Phthalic
In this test, treat 2 mL of organic compound with anhydride
approx. 8 mL of Lucas reagent (for preparing Lucas O O
reagent dissolve 32 g of anhyd. ZnCl2 in 20 mL of
–
conc. HCl) and shake them properly following C —O C
observations are seen O
• Immediate formation of turbidity indicates the OH–
C C
presence of tertiary alcohol.
• Formation of turbidity after 4-5 min shows the
presence of secondary alcohols. –
O O HO OH
• If solution remains clear, then primary alcohol is (Pink colour Phenolphthalein
present. in alkaline) (colourless)
, Principles Related to Practical Chemistry 1189
Phenolphthalein is used as an indicator in acid-base Note This test is usually given by only aliphatic aldehydes,
titrations. It is colourless in acidic medium and pink in thus used to differentiate between aliphatic and aromatic
basic medium. aldehydes.
Tests for Aldehyde (¾CHO) Group æR ö
Tests for Ketone çç C == O÷ Group
÷
(i) Tollen’s reagent test Take a little quantity of the èR ø
compound in a test tube and add 2 mL of freshly
(i) 2,4-dinitrophenyl hydrazine test In a dry test
prepared reagent. Shake, warm and allow the contents
tube, add few drops of the organic compound (if
to stand for 2-3 minutes.
liquid) or its alcoholic solution (if solid) to about
Formation of silver mirror or a grey ppt. indicates the 2 mL of the reagent and one drop of conc. H 2SO4.
presence of an aldehydic group.
- +
Shake vigorously, heat (if necessary) and allow to
2Ag(NH3 )2 OH + R × CHO ¾® 2Ag ¯ + RCO O NH4 stand for about 5 minutes.
Silver mirror
or grey ppt.
+ 3NH3 + H2O A yellow or orange ppt. separates out in case of a
(ii) Fehling’s solution test Take a mixture of equal compound containing carbonyl group due to the
amounts of Fehling’s solution A and B, and add few formation of respective hydrazones.
drops of organic compound and boil the contents.
Formation of a red ppt. shows the presence of an C O + H2N.HN— —NO2
aldehyde. Carbonyl
compound
2CuO + R × CHO ¾® Cu2O ¯ + RCOOH NO2
Cupric Aldehyde
Red ppt. 2, 4-dinitrophenyl hydrazine
oxide
Note
• Both the above tests are also given by reducing sugars.
• Benzaldehyde does not reduce Fehling’s solution C N.HN— —NO2 ¯ + H2O
(a distinction from other aldehydes). Benzaldehyde is
confirmed by malachite green test. NO2
(iii) Schiff’s reagent test Add 5-6 drops of organic Yellow or orange red coloured crystalline
compound to 2 mL of the Schiff 's reagent. Shake derivative of 2, 4-dinitrophenyl hydrazine
vigorously. After some time formation of a deep red or of carbonyl compound
violet colour indicates the presence of an aldehydic
(ii) Sodium bisulphite test Add a very small quantity
group.
of organic compound to 1 mL of saturated solution
H.SO2NH
of sodium bisulphite and shake vigorously.
Formation of white ppt. shows the presence of
.
C— NH2SO2H 2R CHO carbonyl group.
–H2SO4
H.SO2NH SO3H OH
Shake
C == O + NaHSO3 ¾¾® C
Schiff’s reagent (colourless) – +
SO3 Na
Sodium bisulphite
R.CHSO2.NH derivative of
carbonyl compound
(white crystalline ppt.)
OH C NH2
(iii) Sodium nitroprusside test Add 0.1 g of solid or
R.CHSO2.NH 0.2 cc of liquid compound to 2 cc of sodium
OH nitroprusside, Na 2 [Fe(CN)5 NO] solution. After
Violet colour that make the solution alkaline with 2-3 drops of
(iv) Benedict’s solution test Boil the compound with sodium hydroxide. A red or purple colour indicates
2-3 mL of Benedict’s solution for few minutes. the presence of ketone (benzophenone does not
Appearance of a red-yellow ppt. confirms the presence give this test).
of aliphatic aldehydes.
Principles Related to
Practical Chemistry
Experimental (practical) chemistry involves the study of concerned material IN THIS CHAPTER ....
under specific experimental conditions. It can be divided into two branches :
synthetic chemistry and analytical chemistry. Qualitative Analysis of Organic
Compounds
Qualitative Analysis of Organic Compounds Preparation of Inorganic
Compounds
Two major steps involved in the characterisation of an organic compound are
(i) Element detection (For it see chapter 12 purification and characterisation Preparation of Organic
of organic compounds) (ii) Detection of functional group. Compounds
Practical Inorganic Chemistry
Detection of Functional Groups
Element detection shows the presence or absence of different elements. On
the basis of element present, the test of corresponding functional group is
performed.
Tests for different functional groups are given below
Tests for Carboxylic (— COOH) Group
(i) Litmus paper test Dip blue litmus paper in the aqueous solution or
suspension of the compound. It turns red.
(ii) Sodium bicarbonate test In a test tube, take a little quantity of the
compound and then, add a saturated solution of sodium bicarbonate.
Formation of brisk effervescence due to the formation of CO2 shows the
presence of ¾ COOH group.
–+
®
COOH + NaHCO3 COONa + H2O + CO2
Benzoic acid Sodium benzoate
,1188 JEE Main Chemistry
(iii) Ester formation Heat a small quantity of organic Tests for Phenolic (Ph¾ OH) Group
compound with ethyl alcohol and a little conc. H 2SO4 ×
Cool the solution and pour in a tube containing (i) Ferric chloride test Take few drops of ferric
water. A fruity smell, due to formation of an ester, chloride solution and add 2-3 drops of the compound
indicates the presence of carboxylic group. to it. Appearance green, blue or violet colour shows
the presence of phenol.
Conc. H2SO 4
R ¾ COOH + C2H5 OH ¾¾¾¾¾® RCOOC2H5 + H2O 6C6 H5 OH + FeCl3 ¾® 3H+ + [Fe(OC6 H5 )6 ]3 - + 3HCl
D
Carboxylic acid Ethanol Ester Phenol Ferric Violet
(fruity smell) chloride
This test is also given by enols.
Tests for Alcoholic (—OH) Group
(ii) Liebermann’s nitroso reaction Take little amount
(i) Sodium test In a test tube, take some organic of compound and add 1mL of conc. H 2SO4 to it. Shake
compound and add a thin piece of sodium metal to it. and warm the test tube. Cool and then add crystals of
A brisk effervescence due to the formation of sodium nitrite (NaNO2 ).
hydrogen gas takes place.
- + A deep green to blue solution is formed which turns
2ROH + 2Na ¾® 2R ONa + H 2 red on dilution. The red aqueous solution becomes
(ii) Ester test Heat the given compound with acetic acid again deep green or blue if made alkaline with
in the presence of sulphuric acid. A fragrance of NaOH. It shows the presence of phenol.
fruity smell indicates the formation of ester. C6H5OH, H2SO4
HNO2
Conc. H 2SO4 —OH HO— —NO
ROH + CH3 COOH CH3 COOR + H2O
Acetic acid Ester Phenol
(fruity smell) NaOH
O N OH
Alcohols give crystalline esters with 3,5-dinitrobenzoyl
chloride. These esters have sharp melting points and
Indophenol ion
can be used for testing a given alcohol.
–
O NO2 O NO2
O N O
ROH + Cl—C— R—O—C— + HCl
Indophenol (blue)
NO2 NO2
3, 5-dinitrobenzoyl Crystalline ester
chloride Note Nitrophenol do not respond to FeCl3 test as well as
Liebermann’s nitroso reaction.
(iii) Ceric ammonium nitrate test To small amount of
(iii) Phthalein test Phenol on heating with phthalic acid
organic compound or its aqueous solution, add a few
in presence of conc. H 2SO4 gives colourless compound
drops of ceric ammonium nitrate. A red colour
called phenolphthalein, which appear pink coloured
indicates the presence of alcoholic hydroxy group. compound in alkaline medium.
2ROH + (NH4 )2 Ce(NO3 )6 ¾® Ce(NO3 )4 × (ROH)2 O
Alcohol Ceric ammonium O
Red colour
nitrate
+ 2NH4 NO3 C
—C—OH H2SO4, D 2C6H5OH, D
This test is useful when the compound contains less O
—C—OH
than 10 C-atoms. C
(iv) Lucas test This test is used to distinguish between O
primary, secondary and tertiary alcohols. Phthalic acid O
Phthalic
In this test, treat 2 mL of organic compound with anhydride
approx. 8 mL of Lucas reagent (for preparing Lucas O O
reagent dissolve 32 g of anhyd. ZnCl2 in 20 mL of
–
conc. HCl) and shake them properly following C —O C
observations are seen O
• Immediate formation of turbidity indicates the OH–
C C
presence of tertiary alcohol.
• Formation of turbidity after 4-5 min shows the
presence of secondary alcohols. –
O O HO OH
• If solution remains clear, then primary alcohol is (Pink colour Phenolphthalein
present. in alkaline) (colourless)
, Principles Related to Practical Chemistry 1189
Phenolphthalein is used as an indicator in acid-base Note This test is usually given by only aliphatic aldehydes,
titrations. It is colourless in acidic medium and pink in thus used to differentiate between aliphatic and aromatic
basic medium. aldehydes.
Tests for Aldehyde (¾CHO) Group æR ö
Tests for Ketone çç C == O÷ Group
÷
(i) Tollen’s reagent test Take a little quantity of the èR ø
compound in a test tube and add 2 mL of freshly
(i) 2,4-dinitrophenyl hydrazine test In a dry test
prepared reagent. Shake, warm and allow the contents
tube, add few drops of the organic compound (if
to stand for 2-3 minutes.
liquid) or its alcoholic solution (if solid) to about
Formation of silver mirror or a grey ppt. indicates the 2 mL of the reagent and one drop of conc. H 2SO4.
presence of an aldehydic group.
- +
Shake vigorously, heat (if necessary) and allow to
2Ag(NH3 )2 OH + R × CHO ¾® 2Ag ¯ + RCO O NH4 stand for about 5 minutes.
Silver mirror
or grey ppt.
+ 3NH3 + H2O A yellow or orange ppt. separates out in case of a
(ii) Fehling’s solution test Take a mixture of equal compound containing carbonyl group due to the
amounts of Fehling’s solution A and B, and add few formation of respective hydrazones.
drops of organic compound and boil the contents.
Formation of a red ppt. shows the presence of an C O + H2N.HN— —NO2
aldehyde. Carbonyl
compound
2CuO + R × CHO ¾® Cu2O ¯ + RCOOH NO2
Cupric Aldehyde
Red ppt. 2, 4-dinitrophenyl hydrazine
oxide
Note
• Both the above tests are also given by reducing sugars.
• Benzaldehyde does not reduce Fehling’s solution C N.HN— —NO2 ¯ + H2O
(a distinction from other aldehydes). Benzaldehyde is
confirmed by malachite green test. NO2
(iii) Schiff’s reagent test Add 5-6 drops of organic Yellow or orange red coloured crystalline
compound to 2 mL of the Schiff 's reagent. Shake derivative of 2, 4-dinitrophenyl hydrazine
vigorously. After some time formation of a deep red or of carbonyl compound
violet colour indicates the presence of an aldehydic
(ii) Sodium bisulphite test Add a very small quantity
group.
of organic compound to 1 mL of saturated solution
H.SO2NH
of sodium bisulphite and shake vigorously.
Formation of white ppt. shows the presence of
.
C— NH2SO2H 2R CHO carbonyl group.
–H2SO4
H.SO2NH SO3H OH
Shake
C == O + NaHSO3 ¾¾® C
Schiff’s reagent (colourless) – +
SO3 Na
Sodium bisulphite
R.CHSO2.NH derivative of
carbonyl compound
(white crystalline ppt.)
OH C NH2
(iii) Sodium nitroprusside test Add 0.1 g of solid or
R.CHSO2.NH 0.2 cc of liquid compound to 2 cc of sodium
OH nitroprusside, Na 2 [Fe(CN)5 NO] solution. After
Violet colour that make the solution alkaline with 2-3 drops of
(iv) Benedict’s solution test Boil the compound with sodium hydroxide. A red or purple colour indicates
2-3 mL of Benedict’s solution for few minutes. the presence of ketone (benzophenone does not
Appearance of a red-yellow ppt. confirms the presence give this test).
of aliphatic aldehydes.
