Molarity and Normality are two common terms in pharmaceutical analytical chemistry. That’s why the calculation of molarity and normality is basic learning for pharmacy and chemistry students.
Molarity Calculation Formula with Example
Molarity (M) is defined as the number of moles of solute per liter of solution. The solute is defined as the substance being dissolved, while the solvent is the substance where the solute is dissolved (usually water).
Example: Preparation of 500 ml 0.1M NaOH solution (Mol. wt. of NaOH = 40)
0.1 = (1000 x W) / (500 x 40)
W = 2.0 g
To prepare 0.1M NaOH solution, dissolve 2.0 g of sodium hydroxide pellets in 250 ml distilled water and make up the volume to 500 ml.
Normality Calculation Formula with Example
Normality (N) is defined as the number of equivalent weight of solute per liter of solution. Equivalent weight is molecular mass of substance divided by its number of replaceable H+ ions or OH- ions or valency or number of electrons.
Example: Preparation of 1000 ml 1N H2SO4 solution (Mol. wt. of H2SO4 = 98)
Number of replaceable H+ ions per mole = 2 and therefore E= 98/2 =49
Thus,
1 = (1000 x W) / (1000 x 49)
W = 49.0 g
1N Sulphuric acid solution is prepared by dissolving 49.0 g in 1000 ml.
Relationship Between Normality and Molarity
Where molarity describes the moles of a complete substance per liter of solution, normality describes only the moles of reactive species per liter of solution. Normality is always a multiple of molarity. It describes the “equivalent” moles of reactants involved in chemical reactions.
Simply,
N (normality) = M (molarity) x n (number of equivalents)
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