Basicity and Acidity

BASICITY OF ACIDS,
ACIDITY OF BASES
Dr.Shinomol George K
• BASICITY OF ACIDS
• Basicity: the basicity of a molecule is a measure of its ability to accept a proton (H+) to
form a stable product.
• If the product is a cation, then anything that stabilizes the positive charge will increase the
strength of the base.
• The Basicity of an acid is defined as the number of replaceable hydrogen atoms of that
particular acid by a base.
• This should not be misinterpreted as the number of hydrogen atoms in that acid.
• For example, Hypophosphorous Acid H3PO2 has 3 hydrogen atoms but only one
replaceable hydrogen.
• Thus it is monobasic.
• We must be aware that replaceable hydrogen atoms are the ones that are bonded with
the oxygen atoms and not the ones that are bonded to the central metal atom.
• The ones that are directly bonded play a reducing character.
• The required basicity of the compounds according to the above mentioned concept of
replaceable H atoms are:
• Nitric acid: Basicity =1 …..HNO3
Sulphuric acid : Basicity =2 H2SO4
Phosphoric acid : Basicity =3 H3PO4
• Mono-basic acids:
Acids which on ionisation produces on hydronium ion in water are termed as mono-basic
acids.
Example: HCl
Di-basic acids:
Acids which on ionisation produces two hydronium ions are called as di-basic acids.
Example: H2SO4, H2CO3..etc
Tri-basic acids:
Acids which on ionisation produces three hydronium ions are called astri-basic acids.
Example: H3PO4, H3PO3..etc
Acid Basicity
HCl H+ + Cl- 1 Monobasic
H2SO4 2H+ + SO42- 2 Monobasic
H3PO4 3H+ + PO42- 3 Monobasic
CH3COOH H+ + CH3COO- 1 Monobasic

ACIDITY OF BASES
• Acidity of a base is referred as the number of OH- ions present in the base
• For example in Mg(OH)2 there are 2 OH- ions are present so the acidity of
Mg(OH)2 is 2.
• The number of ionizable hydroxide (OH-) ions present in one molecule of
base is called the acidity of bases.
• On the basis of acidity bases can be classified into three types:
monoacidic, diacidic and triacidic.
• Monoacidic bases
• When one molecule of a base via complete ionization produces one hydroxide ion, the
base is said to be a monoacidic base. Examples of monoacidic bases are:
Sodium hydroxide, potassium hydroxide, silver hydroxide, ammonium hydroxide, etc
• Diacidic bases
• When one molecule of base via complete ionization produces two hydroxide ions, the
base is said to be diacidic. Examples of diacidic bases are:
Barium hydroxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide,
iron(II) hydroxide, tin(II) hydroxide, lead(II) hydroxide, copper(II) hydroxide, etc.
• Triacidic bases
• When one molecule of base via complete ionization produces three hydroxide ions, the
base is said to be triacidic. Examples of triacidic bases are:
Aluminium hydroxide, ferrous hydroxide, Gold Trihydroxide,
Acidity basicity
The acidity of bases is the number of The basicity of the acids is the number of
hydroxyl ions that the basic molecule can hydronium ions that the compound can
produce in the aqueous solution. produce in the aqueous solution.
The acidity of a Bronsted acid can be For Bronsted bases basicity means tendency
expressed by the help acid dissociation of a compound to act like (proton)
constant of the compound in water or acceptor.The basicity of a chemical
some other specified medium. The compound is expressed by the acidity of the
measure of acidity is the pH scale. conjugate acid
• AVOGADRO'S NUMBER
• It certainly is easy to count objects such as bananas, or something as large as
elephants (as long as you stay out of their way).
• However, counting grains of sugar from a sugar canister would take a long,
long time.
• Atoms and molecules are extremely small—far, far smaller than grains of
sugar.
• Counting atoms or molecules is not only unwise, it is absolutely impossible.
• One drop of water contains about about 1022 molecules of water.
• Chemists of the past needed a name that could stand for a very large number
of items.
• Amadeo Avogadro (1776-1856), an Italian scientist, provided such a number.
• He is responsible for the counting unit of measure called the mole.
• mole (mol)(mol) is the amount of a substance that contains 6.02× 1023.
representative particles of that substance.
• The mole is the SI unit for amount of a substance. Just like the dozen and the
gross, it is a name that stands for a number.
• There are therefore 6.02× 1023. water molecules in a mole of water molecules.
• There also would be 6.02× 1023. bananas in a mole of bananas, if such a huge
number of bananas ever existed
• The number 6.02×10236.02×1023 is called Avogadro's number, the number of
representative particles in a mole.
• It is an experimentally determined number.
• A representative particle is the smallest unit in which a substance naturally exists.
• For the majority of elements, the representative particle is the atom.
• Iron, carbon, and helium consist of iron atoms, carbon atoms, and helium atoms,
respectively.
• Seven elements exist in nature as diatomic molecules and they
are H2H2, N2N2, O2O2, F2F2, Cl2Cl2, Br2Br2, and I2I2.
• The representative particle for these elements is the molecule.
• Likewise, all molecular compounds such as H2OH2O and CO2CO2 exist as molecules and
so the molecule is their representative particle.
• For ionic compounds such as NaCland Ca(NO3)2, the representative particle is the
formula unit.
• A mole of any substance contains Avogadro's number (6.02× 1023.) of representative
particles.
• One mole of a substance is composed of an Avogadro’s number of
particles.
• These particles can be atoms, ions, molecules, colloids, etc.
• The particle that is being considered depends on the nature of the
substance that is being considered.
• This term is useful in determining the atomic masses and molecular
masses since Avogadro’s number indicates the number of atoms
present in one mole of a chemical element or the number of
molecules present in a particular compound.
Main Difference – Avogadro’s Constant vs Avogadro’s Number
• The terms, mole, Avogadro’s number and Avogadro’s constant are related to each
other.
• A mole is a unit used to measure the amount of a substance. It can be used to
measure any type of chemical substance.
• The value of one mole is 6.022 x 1023. This is called the Avogadro’s number.
• Avogadro’s number is the number of particles present in one mole of a substance.
• The mole of any substance is equal to this number of particles.
• These particles can be atoms, molecules, colloids or anything.
• Therefore, it is a constant number that is independent of the type of substance that
is considered and is called the Avogadro’s constant.
• The main difference between Avogadro’s number and Avogadro’s constant is
that Avogadro’s number is given as a number that has no units whereas the
Avogadro’s constant is given in the unit of per mole (mol-1).

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BASICITY OF ACIDS,

H2SO4 2H+ + SO42- 2 Monobasic

H3PO4 3H+ + PO42- 3 Monobasic

CH3COOH H+ + CH3COO- 1 Monobasic

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