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Class 10, Science, Chapter-4, Lecture-6, Alcohols and Acids (Notes)

FUNCTIONAL GROUP:

An atom or a group of atoms in an organic molecule that is responsible for the compound’s characteristic reactions and determines its properties is known as a functional group.

ALCOHOLS:

The compounds of carbon with hydrogen and oxygen which contain hydroxyl (–OH) as principal functional group are called alcohols.

General Formula – CnH2n+1OH

HOMOLOGOUS SERIES OF ALCOHOLS

MOLECULAR FORMULA
IUPAC NAME
COMMON NAME
CH3OH Methanol Methyl alcohol
C3H7OH Ethanol Ethyl alcohol
C4H9OH Propanol Propyl alcohol
C2H5OH Butanol Butyl alcohol

PHYSICAL PROPERTIES OF ETHANOL:

1.Physical State– Colourless liquid
2.Boiling point – 351 K (78 OC)
3.Solubility – Readily soluble in water

CHEMICAL PROPERTIES OF ETHANOL:

1.Combustion:

$$\mathop {{{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{5}}}{\rm{OH}}}\limits_{{\rm{ethanol}}} {\rm{ + 3 }}{{\rm{O}}_{\rm{2}}} \to 2{\rm{ C}}{{\rm{O}}_{\rm{2}}}{\rm{ + }}\mathop {{\rm{3 }}{{\rm{H}}_{\rm{2}}}{\rm{O}}}\limits_{{\rm{water}}} $$

2.Oxidation:

       Ethanol oxidises to ethanoic acid when heated with alkaline potassium permanganate or acidified potassium dichromate.

$$\mathop {{{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{5}}}{\rm{OH}}}\limits_{{\rm{ethanol}}} {\rm{ + }}\mathop {{\rm{2 [O]}}}\limits_{{\rm{nascent ~oxygen}}} \mathrel{\mathop{\kern0pt\longrightarrow}
\limits_{{\rm{Heat}}}^{{\rm{Alkaline KMn}}{{\rm{O}}_{\rm{4}}}}} \mathop {{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{COOH}}}\limits_{{\rm{ethanoic ~acid}}} {\rm{ + }}\mathop {{{\rm{H}}_{\rm{2}}}{\rm{O}}}\limits_{{\rm{water}}} $$

$$\mathop {{{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{5}}}{\rm{OH}}}\limits_{{\rm{ethanol}}} {\rm{ + }}\mathop {{\rm{2 [O]}}}\limits_{{\rm{nascent~ oxygen}}} \mathrel{\mathop{\kern0pt\longrightarrow} \limits_{{\rm{Heat}}}^{{\rm{Acidified }}{{\rm{K}}_{\rm{2}}}{\rm{C}}{{\rm{r}}_{\rm{2}}}{{\rm{O}}_{\rm{7}}}}} \mathop {{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{COOH}}}\limits_{{\rm{ethanoic~ acid}}} {\rm{ + }}\mathop {{{\rm{H}}_{\rm{2}}}{\rm{O}}}\limits_{{\rm{water}}} $$

3.Reaction with sodium metal:

       Ethanol reacts with sodium to form SODIUM ETHOXIDE and liberate HYDROGEN gas.

$$2\mathop {{{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{5}}}{\rm{OH}}}\limits_{{\rm{ethanol}}} {\rm{ + }}\mathop {{\rm{2 Na}}}\limits_{{\rm{sodium}}} \buildrel {} \over
 \longrightarrow 2\,\,\mathop {{{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{5}}}{\rm{ONa}}}\limits_{{\rm{sodium~ ethoxide}}} {\rm{ + }}\mathop {{{\rm{H}}_{\rm{2}}}}\limits_{{\rm{hydrogen~ gas}}} $$

4.Dehydration of Ethanol

       Ethanol loses water molecule when heated at 443 K in the excess of concentrated sulphuric acid and forms ethene.

$$\mathop {{{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{5}}}{\rm{OH}}}\limits_{{\rm{ethanol}}} \mathrel{\mathop{\kern0pt\longrightarrow}
\limits_{{\rm{443 K}}}^{{\rm{conc}}{\rm{. }}{{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}}}} \mathop {{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{ = C}}{{\rm{H}}_{\rm{2}}}}\limits_{{\rm{ethene}}} {\rm{ + }}\mathop {{\rm{ }}{{\rm{H}}_{\rm{2}}}{\rm{O}}}\limits_{{\rm{water}}} $$

HARMFUL EFFECTS OF DRINKING ALCOHOL:

1.Methanol causes poisoning and loss of eyesight.
2.A person becomes addicted to alcohol if it is consumed regularly.
3.A person loses sense of discrimination.
4.Excessive intake of alcohol damages liver and may cause death.

CARBOXYLIC ACIDS:

The compounds of carbon, hydrogen and oxygen which contain carboxyl (–COOH) as principal functional group are called carboxylic acids.

General Formula - CnH2n+1COOH

HOMOLOGOUS SERIES OF CARBOXYLIC ACIDS:

MOLECULAR FORMULA
IUPAC NAME
COMMON NAME
HCOOH Methanoic Acid Formic Acid
CH3COOH Ethanoic Acid Acetic Acid
C2H5COOH Propanoic Acid Propionic Acid
C3H7COOH Butanoic Acid Butyric Acid

VINEGAR:

Dilute solution of acetic acid in water that contains 5% to 8% of acetic acid is termed as vinegar.

PHYSICAL PROPERTIES OF ACETIC ACIDS:

1.Physical State: Colourless liquid
2.Boiling point: 391 K (118 OC)
3.Solubility: Readily soluble in water

CHEMICAL PROPERTIES OF ETHANOIC ACID:

1.Reaction with Metal Hydroxides:

Forms metal ethanoate and H2O

$${\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{COOH}}\,{\rm{ + }}\,{\rm{NaOH}}\buildrel {} \over
 \longrightarrow \mathop {{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{COONa}}}\limits_{{\rm{SODIUM ~ ETHANOATE}}} {\rm{ + }}\,{{\rm{H}}_{\rm{2}}}{\rm{O}}$$

2.Reaction with Metal Carbonates or Metal Hydrogen carbonates:

Forms metal ethanoate and H2O, and liberate CO2 gas

$${\rm{2}}\,{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{COOH + }}\,{\rm{N}}{{\rm{a}}_{\rm{2}}}{\rm{C}}{{\rm{O}}_{\rm{3}}}\buildrel {} \over \longrightarrow \mathop {{\rm{2 C}}{{\rm{H}}_{\rm{3}}}{\rm{COONa}}}\limits_{{\rm{SODIUM ~ ETHANOATE}}} \,{\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{O + C}}{{\rm{O}}_{\rm{2}}}$$

$${\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{COOH}}\,{\rm{ + }}\,{\rm{NaHC}}{{\rm{O}}_{\rm{3}}}\buildrel {} \over
 \longrightarrow \mathop {{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{COONa}}}\limits_{{\rm{SODIUM~ETHANOATE}}} {\rm{ + }}\,{{\rm{H}}_{\rm{2}}}{\rm{O + C}}{{\rm{O}}_{\rm{2}}}$$

3.Reaction with Alcohols (Esterification):

Ethanoic Acid reacts with alcohols on heating in the presence of concentrated H2SO4 to produce ester and water.

$$\mathop {{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{COOH}}}\limits_{{\rm{ethanoic~ acid}}} {\rm{ + }}\mathop {{{\rm{C}}_{\rm{3}}}{{\rm{H}}_{\rm{7}}}{\rm{OH}}}\limits_{{\rm{propanol}}} \mathrel{\mathop{\kern0pt\longrightarrow}
\limits_{{\rm{Heat}}}^{{\rm{conc}}{\rm{. }}{{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}}}} \mathop {{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{COO}}{{\rm{C}}_{\rm{3}}}{{\rm{H}}_{\rm{7}}}}\limits_{{\rm{propyl ~ethanoate}}} {\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{O}}$$