Wednesday, September 1, 2021

4. Carbon and its Compounds | Class 10 CBSE | Web Notes - Part 4

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 (2CH3CH2ONa+) & H2.

2Na + 2CH3CH2OH → 2CH3CH2ONa+ + 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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