Normality Formula

Normality is a rarely used expression which indicates the concentration of a solution. It is defined as the gram equivalent weight per liter of solution.

The reason normality is rarely used lies in the definition of gram equivalent weight. Gram equivalent weight is determined by the amount of an ion that reacts, which could change depending on the reaction. The fact that the gram equivalent weight is not a consistent amount creates confusion and leads scientists to use other concentration values.

Normality, when used, is typically done so in acid base reactions. Here, a more favorable calculation for normality is considered, where the normality of a solution is equal to the molarity multiplied by the number of equivalents.

Normality Formula Questions:

1. What is the normality of 1.0 M H₂SO₄ in the following reaction?

Answer:

In this reaction, 2 moles of H+ ions (2 equivalents)from sulfuric acid (H₂SO₄) react with NaOH to form sodium sulfate and water.

Normality(N) = Molarity(M) x number of equivalents

Normality(N) = 1.0 x 2

Normality(N) = 2.0

2. What is the normality of 1.0 M H₃PO₄ in the following reaction?

Answer:

In this reaction, only 2 of the three available H+ ions (2 equivalents) from arsenic acid (H₃AsO₄) react with NaOH to form Na₂HAsO₄ and water.

Normality(N) = Molarity(M) x number of equivalents

Normality(N) = 1.0 x 2

Normality(N) = 2.0