How to Calculate Normality?

Normality is calculated by dividing the number of equivalents of a solute by the volume of the solution in liters.

Normality (N) = (Equivalents of solute) / (Volume of solution in Liters)

Here's a breakdown of the components and how to determine them:

Understanding the Terms

Normality (N): A measure of concentration expressed as the number of equivalents of solute per liter of solution.
Equivalents of Solute: This depends on the type of reaction the solute undergoes.
- For Acids: The number of equivalents is the number of moles of replaceable hydrogen ions (H⁺) per mole of acid. For example, HCl has one equivalent per mole, while H₂SO₄ has two equivalents per mole.
- For Bases: The number of equivalents is the number of moles of replaceable hydroxide ions (OH⁻) per mole of base. For example, NaOH has one equivalent per mole, while Ba(OH)₂ has two equivalents per mole.
- For Salts: The number of equivalents is based on the total positive or negative charge provided by the salt per mole. For example, for NaCl, the equivalent is one (1 mole of Na⁺ with +1 charge). For CaCl₂, the equivalent is two (1 mole of Ca²⁺ with +2 charge).
Volume of Solution: Must be expressed in liters (L). Remember that 1 liter = 1000 milliliters.

Determine the number of moles of solute. This can be calculated using the formula:

Moles = (Mass of solute) / (Molar mass of solute)
Determine the number of equivalents per mole of solute. This depends on whether the solute is an acid, base, or salt, as described above.
Calculate the number of equivalents of solute:

Equivalents = (Moles of solute) * (Equivalents per mole)
Determine the volume of the solution in liters. Convert from milliliters (mL) to liters (L) if necessary:

Liters = Milliliters / 1000
Calculate the normality:

Normality (N) = (Equivalents of solute) / (Volume of solution in Liters)

Let's say you dissolve 4.9 grams of sulfuric acid (H₂SO₄) in enough water to make 250 mL of solution. What is the normality of the solution?

Moles of H₂SO₄: The molar mass of H₂SO₄ is approximately 98 g/mol.

Moles = 4.9 g / 98 g/mol = 0.05 moles
Equivalents per mole: H₂SO₄ has two replaceable hydrogen ions (H⁺), so it has 2 equivalents per mole.
Equivalents of H₂SO₄:

Equivalents = 0.05 moles * 2 equivalents/mole = 0.1 equivalents
Volume of solution in liters:

Liters = 250 mL / 1000 mL/L = 0.25 L
Normality:

Normality = 0.1 equivalents / 0.25 L = 0.4 N

Therefore, the normality of the sulfuric acid solution is 0.4 N.

Normality is highly context-dependent because the number of equivalents depends on the specific reaction.
Molarity and normality are related. For example, for H₂SO₄, Normality = 2 x Molarity, because there are two equivalents per mole.
Normality is often used in titration calculations.