Defining Normality in Chemistry
Normality (N) is a measure of concentration that expresses the number of gram equivalent weights of a solute per liter of solution. Unlike molarity, which is based on moles, normality is based on the reactive capacity of a substance in a specific chemical reaction, making it particularly useful for acid-base and redox titrations.
Section 2: The Concept of an 'Equivalent'
The core of normality is the 'equivalent' (Eq). An equivalent is the amount of a substance that can either donate or accept one mole of another substance. For an acid, one equivalent is the amount that donates one mole of protons (H⁺). For a base, it's the amount that accepts one mole of protons. In redox reactions, an equivalent is the amount that donates or accepts one mole of electrons.
Section 3: A Practical Example
Consider a 1 M (molar) solution of sulfuric acid (H₂SO₄) for an acid-base reaction. Since each molecule of H₂SO₄ can donate two protons (2 H⁺), one mole of H₂SO₄ provides two equivalents of H⁺. To find its normality, you multiply its molarity by the number of equivalents per mole (the n-factor). So, 1 M H₂SO₄ has a normality of 2 N (1 mol/L × 2 Eq/mol).
Section 4: Importance and Application
The primary advantage of normality is that it simplifies titration calculations. The formula V₁N₁ = V₂N₂ allows for a direct comparison of the volumes of two solutions that will completely react, regardless of the stoichiometry of the reaction. One liter of any 1 N acid will perfectly neutralize one liter of any 1 N base.