4. CARBON AND ITS COMPOUNDS
SOME
IMPORTANT CARBON COMPOUNDS: ETHANOL & ETHANOIC ACID
Properties of Ethanol
Ethanol is liquid at room temperature.
It is commonly
called alcohol and is the active ingredient of all alcoholic drinks.
It is a good
solvent. So it is used in medicines such as tincture iodine, cough syrups,
and tonics.
Ethanol is
soluble in water in all proportions.
Consumption of
small quantities of dilute ethanol causes drunkenness. Intake of even a
small quantity of pure ethanol (absolute alcohol) is lethal. Long-term
intake leads to many health problems.
Ethanol for
industrial use is made unfit for drinking by adding methanol. It is called denatured
alcohol. Blue dyes are added to alcohol to identify easily.
Some countries
use alcohol as an additive in petrol since it is a cleaner fuel. It releases
only CO2 & water.
Reactions of
Ethanol
a. Reaction with
sodium:
Alcohols react
with sodium evolving hydrogen. E.g. Drop a small piece of sodium into pure ethanol.
It produces sodium ethoxide (2CH3CH2O–Na+) & H2.
2Na + 2CH3CH2OH
→ 2CH3CH2O–Na+ + H2
b. Reaction to give
unsaturated hydrocarbon:
Heating ethanol
at 443 K with excess conc. H2SO4 results in dehydration
of ethanol to give ethene. Conc. H2SO4 is a
dehydrating agent (removes water from ethanol).
Properties of Ethanoic acid (Acetic acid)
It belongs to carboxylic acids (weak acids).
5-8% solution of
acetic acid in water is called vinegar. It is used as a preservative in
pickles.
The melting
point of pure ethanoic acid is 290 K and hence it often freezes during
winter. So it is known as glacial acetic acid.
Acetic acid is
weak acid and HCl is a strong acid.
Reactions of
ethanoic acid:
a.
Esterification reaction: It is the formation of esters by the reaction of an acid and an alcohol.
E.g. Take 1 mL absolute
ethanol + 1 mL glacial acetic acid + few drops of conc. H2SO4
in a test tube.
Warm in a water bath for 5 minutes.
Pour into a beaker containing 20-50 mL of water. The resulting mixture is
an ester.
Here, ethanoic
acid reacts with ethanol in presence of an acid catalyst to give an ester.
Esters have a sweet smell.
Uses of esters: To make perfumes & as flavouring agents.
On treating with
NaOH (an alkali), the ester is converted back to alcohol and sodium salt of
carboxylic acid. This reaction is called saponification because it is
used in the preparation of soap.
b. Reaction with a base:
Ethanoic acid
reacts with a base like NaOH to give a salt (sodium ethanoate or sodium
acetate) and water.
NaOH + CH3COOH
→ CH3COONa + H2O
c. Reaction with
carbonates & hydrogen carbonates:
Take a spatula full of sodium carbonate in a test tube and add 2 mL dilute ethanoic acid. Following reaction occurs:
2CH3COOH + Na2CO3 → 2CH3COONa
+ CO2 + H2O
(Sodium acetate)
Pass the gas produced through lime-water. Lime-water turns milky. It means
that the gas is CO2.
Reaction with sodium
hydrogen carbonate:
CH3COOH
+ NaHCO3 → CH3COONa + H2O + CO2
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