A wide variety of materials consists essentially of elements and compounds having different characteristics exist around us. Some of them are sour, some are bitter, while some are salty in taste. For Ex:- Sour and bitter tastes of food are due to acids and bases, respectively, present in them.
Acids react with bases to produce salt whose properties are different from acid and base.
The term "acid" is derived from the latin word "acidus" meaning sour to taste.
Example:- Sour taste of lemon, unripened grapes, Vinegar, tomatoes etc.Fig: Svante Arrhenius
According to Arrhenius theory:- "An acid is a substance which dissolved in water, it ionizes and releases hydrogen ions [H+(aq.)] in solution".
Note- Hydrogen ion do not exist as H+ ions in solution, they attach themselves to the polar water molecules to form hydronium ions or hydroxonium ions, (H3O+ or H+(aq)
(I) Acids are classified as Organic and Mineral acids. Acids which are derived from plants and animals, they are known as Organic Acids. For ex, Citric Acid from fruit. Mineral acids are inorganic acids such as Sulphuric Acid. They are dangerous to be used, so need more precautions.
(i) Mineral Acids (Inorganic acids)-
The acids which are usually obtained from minerals are known as inorganic acids.
|Name||Chemical Formula||Where found or used|
|Hydrochloric acid||HCl||In purification of common salt, in textile industry as a bleaching agent, to make aqua regia.|
|Nitric Acid||H2SO4||Commonly used in car batteries, in the manufacture of fertilizers (Ammonium phosphate, Super phosphate detergents etc, in paints, plastics, drugs)|
|Carbonic Acid||HNO3||manufacture of artificial silk, in petroleum refining.|
|Used in the manufacture of explosives (TNT, Nitroglycerine) and fertilizers (Ammonium nitrate, Calcium nitrate, Purification of Au, Ag.|
|Phosphoric acid||H3PO4||Used in anti-rust paints and in fertilizers|
Note- Aqua regia is a mixture of (3 part HCl & 1 part HNO3 ) which dissolves even noble metals like Au, Pt.
(ii) Organic Acids-
Fig: Citric acid example of organic acids
The acids which are usually obtained from plants and animals are known as organic acids.
|Name||Where found or used|
|Formic acid (HCOOH)||Found in the stings of ants and bees, used in tanning leather, in medicines for treating gout.|
|Acetic acid (CH3COOH)||Found in vinegar, used as solvent in the manufacture of dyes and perfumes.|
|Lactic acid||Responsible for sourcing of milk in curd|
|Benzoic acid||Used as a food preservative|
|Citric acid||Present in lemon, orange and citrus fruits|
|Tartaric acid||Present in tamarind.|
(II) On the Basis of their Basicity:-
"The basicity of an acid is the number of replaceable hydrogen atoms present in a molecule that can be produced by the complete ionisation of one molecule of that acid in aqueous solution."
or "Basicity of an acid is determined by number of hydronium ions (H3O+/H+(aq) produced per molecule of acid on ionisation."
(i) Monobasic Acids-
The acid on complete ionisation produce one hydronium ion in aqueous solution.
Example- Hydrochloric acid (HCl)
Hydrobromic acid (HBr)
Hydrofluoric acid (HF)
Hydroiodic acid (HI)
Nitric acid (HNO3)
Acetic acid (CH3COOH)
Formic acid (HCOOH)
(ii) Dibasic Acid-
The acid on complete ionisation produces two hydronium ions in aqueous solution.
Example- Sulphuric acid (H2SO4)
Carbonic acid (H2CO3)
Oxalic acid (COOH)2
(iii) Tribasic Acid-
The acid on complete ionisation produces three hydronium ions in aqueous solution.
(III) Classification on the basis of their strength:-
(i) Strong Acid-
The acid which undergoes complete ionisation in aqueous solution is known as strong acids.
(ii) Weak Acid-
The acid which undergoes partial or incomplete ionisation in aqueous solution is known as weak acids.
Example- Formic acid (HCOOH)
Oxalic acid (COOH)2
Carbonic acid (H2CO3)
Phosphoric acid (H3PO4)
(IV) Classification on the basis of concentration of the Acid:-
(i) Concentrated Acid-
The acids which contains very small amount of water is called a concentrated acid.
(ii) Dilute Acid-
Fig: Dilution of acidThe acids which contain more amount of water is called a dilute acid.
"Strength of an acid does not depend upon the concentration of an acid"
Strength of an Acid ∝ Concentration of hydronium ion.
Substances with bitter taste and give a soapy touch are known as bases but many bases have corrosive nature.
Properties of Bases:
– Produce hydroxide ions [OH –] in H2O.
– Water soluble bases are called alkalies.
– Bitter Taste
– Turn Red Litmus blue.
– Act as electrolytes in Solution.
– Neutralize solutions containing H+ ions.
– Have a slippery, ‘soapy’ feel.
– Dissolve fatty material.
According to Arrhenius:-
"Those substances which give hydroxide or hydroxyl ion (OH-) in their aqueous solution" are called bases.
NaOH(aq.) → Na+(aq) + OH-(aq)
KOH(aq.) → K+(aq) + OH-(aq)
Example- Sodium hydroxide (NaOH)
Zinc oxide (ZnO)
Copper oxide (CuO)
Calcium hydroxide [Ca(OH)2]
Aluminum hydroxide [Al(OH)3]
The compounds which are either metallic oxides or metallic hydroxides. Which combines with acids to form salts and water only.
Bases which completely dissolves in water are called alkalis.
Examples- KOH, NaOH, Ca(OH)2
All the alkalis are bases but all bases are not alkalis.
Examples- [Fe(OH)3] ferric hydroxide and cupric hydroxide [Cu(OH)2] are base, but not an alkali.
Classification of Bases-
(I) Classification on the basis of their strength:-
(i) Strong alkalis or bases-
The alkalis or bases which undergo almost complete ionisation in aqueous solution are known as strong alkalis or bases.
(ii) Weak alkalis or bases-
The alkalis or bases which undergo only partial ionisation in aqueous solution are known as weak alkalis or Bases.
(II) Classification on the basis of their concentration:-
(i) Concentrated Base or Alkali-
The bases or alkalis which contain a very small amount of water is called concentrated bases or alkalis.
(ii) Dilute Base-
The bases or alkali which contain more amount of water is called a dilute bases or alkalis
(III) Classification on the basis of their acidity:-
Fig: Soaps are basic in natureAcidity of a base is determined by the number of hydroxyl (OH-) ions produced by per molecule of a Base or Alkali on complete dissociation in water "or"
The "number of hydrogen ions of an acid with which a molecule of that alkali or base react to produce salt and water is known as acidity of an alkali or Base".
(i) Mono acidic Bases or Alkali-
The base or alkali on complete ionisation produces one hydroxyl (OH_) ion in aqueous solution.
(ii) Diacidic Bases (or alkalis)-
The base or alkali on complete ionization produce two hydroxyl ion (OH-) in aqueous solution
(A) Diacidic Bases of-
Ca(OH)2(aq.) → Ca2+(aq.) + 2OH-(aq.)
Mg(OH)2(aq.) → Mg2+(aq.) + 2OH-(aq.)
(B) Diacidic Bases -
Ferrous hydroxide [Fe(OH)2] and copper hydroxide [Cu(OH)2]
Fe(OH)2(aq.) → Fe2+ + 2OH-(aq.)
Fe+2(OH)2- + 2H+Cl-(aq.) → FeCl2 + 2H2O
(iii) Tri Acidic Bases-
The base or alkali on complete ionization produces three hydroxyl ion (OH)- in aqueous solution.
Example- Aluminium hydroxide [Al(OH)3], Ferric hydroxide [Fe(OH)3]
Al(OH)3(aq.) → Al3+(aq.) + 3OH-(aq.)
Al3+(OH)3- + 3HCl(aq.) → AlCl3 + 3H2O