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Q2. Suggest chemical test  to distinguish between

 

a)  Phenol and Acetic acid
b)  Formaldehyde and Acetaldehyde
c)   Formic acid and  Acetic acid
d)  Propanoyl Chloride and Propanoic acid

Dear Student,

Chemical test to distinguish between

 a) Phenol and Acetic acid

NaHCO3 test: When both are reacted with NaHCO3, acetic acid gives brisk effervescence due to liberation of CO2 gas. But phenol does not give any reaction with NaHCO3.

CH3COOH + NaHCO3 ----> CH3COONa + CO2 + H2O 

C6H5OH + NaHCO3 ------> no evolution of CO2 gas

b) Formaldehyde and Acetaldehyde

Iodoform test: When both are treated with iodine in presence of alkali, acetaldehyde gives white ppt. of iodoform but formaldehyde not.

CH3CHO + 4NaOH  + 3I2 ----> CHI3  + HCOONa + 3NaI + 3H2O

HCHO + 4NaOH  + 3I2 ----> No Iodoform

c) Formic acid and Acetic acid

Tollen's reagent test : When both are treated with Tollen's reagent, formic acid reduces Tollen's reagent to metallic silver but acetic acid doesn't.

 HCOOH + 2[Ag(NH3)2]+ + 2OH- ---> 2Ag + CO2 + 2H2O + 4NH3

CH3COOH + [Ag(NH3)2]+ ----> no silver mirror

d) Propanoyl Chloride and Propanoic acid

Add a few drops of water to both.

Propanoyl chloride will hydrolyze to give acid and white fumes of HCl. But there will be no fumes in case of Propanoic acid.

CH3CH2COCl + H2O ----> CH3CH2COOH + HCl

CH3CH2COOH + H2O ----> No fumes of HCl

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phenol when reacts with neutral FeCl3, will give a violet colouration.... no one else gives violet colouration.

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 1) PHENOL & ACETIC ACID

NaHCO3 test: acetic acid being a stronger acid than carbonic acid decomposes NaHCO3 to evove CO2 but phenol being a weaker acid than carbonic acid doesnot.

CH3COOH + NaHCO3 ----> CH3COONa + CO2 + H2O

C6H5OH + NaHCO3 ------> no evolution of CO2 gas

FeCl3 test : phenol gives a violet colourationn with neutral FeCl3 solution but acetic acid gives buff coloured ppt. of ferric acetate

C6H5OH + FeCl3 ---> violet colouration

3CH3COOH + FeCl3 ---> (CH3COO)3Fe + 3HCl

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 1) PHENOL & ACETIC ACID

NaHCO3 test: acetic acid being a stronger acid than carbonic acid decomposes NaHCO3 to evove CO2 but phenol being a weaker acid than carbonic acid doesnot.

CH3COOH + NaHCO3 ----> CH3COONa + CO2 + H2O

C6H5OH + NaHCO3 ------> no evolution of CO2 gas

FeCl3 test : phenol gives a violet colouration with neutral FeCl3 solution but acetic acid gives buff coloured ppt. of ferric acetate

C6H5OH + FeCl3 ---> violet colouration

3CH3COOH + FeCl3 ---> (CH3COO)3Fe + 3HCl

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 3) FORMIC ACID AND ACETIC ACID

Tollen's reagent test : formic acid reduces Tollen's reagent to metallic silver but acetic acid doesn't.

HCOOH + 2[Ag(NH3)2]+ + 2OH- ---> 2Ag + CO2 + 2H2O + 4NH3

CH3COOH + [Ag(NH3)2]+ ----> no silver mirror

Fehling's solution test: formic acid reduces fehling's solution to red ppt. of Cu2O but acetic acid doesnot

HCOOH + 2Cu2+ + 4OH- ---> Cu2O + CO2 + 3H2O

CH3COOH + 2Cu2+ + 4OH- ---> no red ppt of Cu2O

HgCl2 test :

formic acid reduces HgCl2 to give wyt ppt of Hg2Cl2 while acetic acid doesnt give this test .

HCOOH + HgCl2 ---> Hg2Cl2 + HCl + CO2

CH3COOH + HgCl2 ---> no wyt ppt of Hg2Cl2

KMnO4 test :

formic acid decolourises the pink color of acidified KMnO4 solution while acetic acid doesn't 

HCOOH + KMnO4 + H2SO4 ---> K2SO4 + MnSO4 + CO2 + H2O

CH3COOH + KMnO4+ H2SO4 ---> does not discharge pink color of KMnO4 sol.

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