Classification of acid

Acid base and salt of Class 8

CLASSIFICATION OF ACID

On the basis of their origin, the acids have been classified into two broad classes, i.e., organic acids and inorganic acids.

(i) Inorganic acids:Acids which are obtained from rocks and minerals are called inorganic or mineral acids.

e.g. HCl, H2SO4, HNO3 etc.

The inorganic acids are further subdivided into strong acids and weak acids.To score More in your class 8 refer NCERT solutions for class 8 .

Strong acids:

The acids in which less than 30% of the molecules of it ionise in water to furnish H+ions are called weak acids.
It is useful to remember that all organic acids are weak acids.

(ii) Organic acids: Acids that are found in animals and plants are known as organic acids.

e.g. (a) Lactic acid (present in sour milk) and citric acid (present in citrus fruits)

Tamarind contains tartaric acid
Vinegar which we use in different foods and as a preservative contains acetic acid.
Formic acid is present in ants. The sharp pain caused by sting of an ant, beatles and bees is due to formic acid, which they push into the body or spray on the skin.

NOTE: Vitamin C which is very important for our body is also an organic acid known as ascorbic acid.

Name	Type	Chemical Formula	Where found or used
Carbonic acid	Mineral acid	H2CO3	In soft drinks and lends fizz, In stomach as gastric juice, used in tanning industry
Nitric acid	Mineral acid	HNO3	Used in the manufacture of explosives (TNT, Nitroglycerine) and fertilizers (Ammonium nitrate, Calcium nitrate, Purification of Au, Ag.
Hydrochloric acid	Mineral acid	HCl	In purification of common salt, in textile industry as bleaching agent, to make aqua regia.
Sulphuric acid	Mineral acid	H2SO4	Commonly used in car batteries, in the manufacture of fertilizers (Ammonium sulphate, super phosphate) detergents etc, in paints, plastics, drugs, in manufacture of artificial silk, in petroleum refining.
Phosphoric acid	Mineral acid	H3PO4	Used in antirust paints and in fertilizers.
Formic acid	Organic acid	HCOOH(CH2O2)	Found in the stings of ants and bees, used in tanning leather, in medicines for treating gout.
Acetic acid	Organic acid	CH3COOH(C2H4O2)	Found in vinegar, used as solvent in the manufacture of dyes and perfumes.
Lactic acid	Organic acid	CH3CH(OH)COOH(C3H6O3)	Responsible for souring of milk in curd.
Benzoic acid	Organic acid	C6H5COOH	Used as a food preservative.
Citric acid	Organic acid	C7H6O2	Present in lemons, oranges and citrus fruits.
Tartaric acid	Organic acid	C4H6O6	Present in tamarind

Preparation of acids:

non-metallic oxide when reacts with water produce acid for example :

Reaction of salt with water :

Physical properties of acids:

They have a sour taste.
They turn blue litmus solution red.
They turn methyl orange solution pink.
They do not affect phenolphthalein solution
Strong acids have corrosive action on skin. They cause painful blisters.
Most of the acids are soluble in water.
Acids contain [H+] or [H3O+] ions.

These ions are responsible for acidic nature.

Chemical Properties of Acids:

ction with metals : Dilute acids like dilute HCI and-dilute H2SO4react with certain active metals to evolve hydrogen gas. Such metals are called active metals like Na, K, Zn, Fe, Ca, Mg etc.

2 Na(s) + 2HCl (dilute) 2NaCl(aq) + H2(g)

Mg(s) + H2SO4(dilute) MgSO4(aq) + H2(g)

The active metals which lie above hydrogen in the activity series are electropositive in nature. Their atoms lose electrons to form positive ions and these electrons are accepted by H+ ions of the acid. As a result, H2 is evolved.

e.g.

(Loss of electrons)

Loss of electron(s) is called oxidation while gain of electron(s) is called reduction.

Action with metal oxides: Acids react with metal oxides to form salt and water. These reactions are mostly carried out upon heating.

For e.g.

Action with metal carbonates and metal bicarbonates: Both metal carbonates and bicarbonates react with acids to evolve CO2 gas and form salts.

Strong and Weak Acids:

Strong acids are almost completely ionised (break up into ions) in water.

e.g.Hydrochloric acid (HCI), sulphuric acid (H2SO4), nitric acid (HNO3) etc. are all strong acids.

HCl + water H+(aq) + NO2−(aq)

H2SO4 + water 2H+(aq) + SO42−(aq)

Weak acidsarepartially ionized in water.

e.g.Carbonic acid (H2CO3), phosphoric acid (H3PO4), formic acid (HCOOH), acetic acid (CH3COOH).

CH3COOH + Water → CH3COO−(aq) + H+(aq) (partially ionized)

Concentrated and dilute Acids:

The strength of an acid can be decreased by dissolving it in excess of water HCI is prepared by dissolving HCI gas in water. The solution of this acid is called conc. HCI. Its strength can be decreased by dissolving the acid in more water. For this purpose, the acid is slowly poured into water while constantly stirring the solution. In a laboratory, we generally use either concentrated acid or its solution diluted to a definite strength. It is called dilute acid.

Uses of acid

Sulphuric Acid

It is used in the manufacture of fertilisers.
It is used in car batteries.
It is used in the manufacture of dyes, drugs, paints, plastics, detergents etc.

Hydrochloric Acid

It is used for cleaning metal surfaces during tinning and galvanising.
It is used in dyeing industry.
It is used for preparing glucose from starch.

Nitric Acid

It is used in the manufacture of fertilisers such as ammonium nitrate and calcium ammonium nitrate.
It is used in the manufacture of explosives such as TNT (trinitrotoluene) and TNG (trinitroglycerine).
It is used in the purification of metals such as gold and silver.

Phosphoric Acid