Normality
Normality is
defined as the number of gram equivalents of a solute contained in 1 litre of a
solution. Thus a solution which contains one gram equivalent of the solute per
litre of the solution is called normal solution. It is represented as 1 N.
Gram
equivalent is the weight of substance in grams numerically equivalent to its
equivalent weight.
Equivalent weights of Acids and Bases:
The equivalent weight
of an acid is that weight of it which contains 1.008 gm of replaceable
hydrogen.
The equivalent weight of a base is that weight of it contains one
replaceable hydroxyl group.
For example, HCl and NaOH have only replaceable H⁺ and OH-hence the equivalent weights of them are equal to their molecular weights.
Equivalent weight of HCl
Molecular weight of HCl = H(1 X 1) + Cl(35.5 X 1)
= 1+35.5
= 36.5
Number of replaceable ions (H⁺) = 1
Gram equivalent weight = molecular weight/number of replaceable ions
Gram equivalent weight = 36.5 gm
Equivalent weight of NaOH
Molecular weight of NaOH = Na (23 X 1) + O (16 X 1) + H (1 X 1)
= 23 + 16 + 1
= 40 gm
Number of replaceable ions (OH-) = 1
Gram equivalent weight = molecular weight/number of replaceable ions
Gram equivalent weight = 40 gm
Sulphuric acid (H₂SO₄) and Oxalic acid
(HOOC-COOH) each have two replaceable hydrogen, hence their equivalent weights
are equal to half of their respective molecular weights.
Equivalent weights of some common Acids:
Acidity: No. of replaceable OH- ions.
Basicity : No. of replaceable H⁺ ions.
Acid
|
Molecular
weight
|
Basicity
|
Equivalent
weight
|
Hydro
Chloric Acid, HCl
|
36.46
|
1
|
36.46
|
Nitric
Acid, HNO₃
|
63.01
|
1
|
63.01
|
Sulphuric
Acid, H₂SO₄
|
98.07
|
2
|
49.03
|
Acetic
Acid, CH₃COOH
|
60.05
|
1
|
60.05
|
Boric
Acid, H₃BO₃
|
61.83
|
3
|
20.61
|
Oxalic
Acid (dihydrate), (COOH)₃,2H₂O
|
126.07
|
2
|
63.03
|
Equivalent weights of
some common Bases:
Base
|
Molecular
weight
|
Acidity
|
Equivalent
weight
|
Sodium
Hydroxide, NaOH
|
40.00
|
1
|
40.00
|
Potassium
Hydroxide, KOH
|
56.11
|
1
|
56.11
|
Sodium
Carbonate, Na₂CO₃
|
105.99
|
2
|
53.00
|
Sodium
bicarbonate, NaHCO₃
|
84.01
|
1
|
84.01
|
Potassium
Carbonate, K₂CO₃
|
138.21
|
2
|
69.10
|
Potassium
bicarbonate, KHCO₃
|
100.12
|
1
|
100.12
|
Specific gravities,
percentage and approximate Normalities of some common Acids:
Acid
|
Specific
gravity
|
Percentage
|
Approximate
normality
|
Concentrated
sulphuric acid
|
1.84
|
Not
less then 97.0 w/w H₂SO₄
|
36N
|
Concentrated
hydrochloric acid
|
1.18
|
35.0
– 38.0 w/w HCL
|
11.5N
|
Concentrated
nitric acid
|
1.42
|
69.0
– 71.0 w/w HNO₃
|
16N
|
Acetic
acid (glacial)
|
1.05
|
Not
less then 99.0 w/w C₂H₄O₂
|
17.5N
|
