The Difference Between Normality and Molarity in Chemistry
When it comes to studying chemistry, two terms that often get used interchangeably are normality and molarity. However, these two terms are not the same and understanding the difference between them is crucial for accurate calculations and experiments.
What is Molarity?
Molarity is a measure of the concentration of a solution that is determined by the amount of solute present in the solution. It is expressed in terms of moles of solute per liter of solution, denoted as ‘M’. For example, a 1 M solution of sodium chloride means that there is one mole of sodium chloride present in a liter of the solution.
What is Normality?
Normality, on the other hand, is a measure of the concentration of a solution that is determined by the number of reactive entities (ions or molecules) present in a solution. It is expressed in terms of the number of equivalents of solute per liter of solution, denoted as ‘N’.
In other words, normality is a measure of how many reactive sites the solute has that can participate in a chemical reaction. For example, a 3 N solution of hydrochloric acid means that there are three equivalents of hydrogen ions present in the solution.
The Key Difference
The key difference between molarity and normality is in their definition. Molarity is based on the number of moles of solute per liter of solution, whereas normality is based on the number of reactive sites of a solute. This is why a mole of a diatomic molecule, such as oxygen or hydrogen, is equivalent to two reactive sites, and therefore, one mole of such a molecule will be equal to two equivalents.
When to Use Molarity or Normality?
Molarity is commonly used when dealing with acid and base reactions, dissolution calculations, and when preparing standard solutions. Normality is often used when dealing with reactions in which the number of reactive sites of a solute is critical, like in redox reactions.
In conclusion, the difference between normality and molarity in chemistry is important and should be understood to correctly interpret and apply chemical reactions. While molarity is based on the number of moles of solute per liter of solution, normality is based on the number of reactive sites of a solute. Therefore, it is essential to use the appropriate terms when performing experiments, making calculations, or interpreting results in the lab.
Table difference between normality and molarity
| Parameter | Normality | Molarity |
|---|---|---|
| Definition | Normality is the number of gram equivalent weights of a solute per liter of solution. | Molarity is the number of moles of a solute per liter of solution. |
| Symbol | N | M |
| Formula | N = (weight of solute ÷ equivalent weight of solute) ÷ volume of solution | M = number of moles of solute ÷ volume of solution |
| Units | gram equivalent weight per liter (gEq/L) | mole per liter (mol/L) |
| Used for | Acid-base titrations, Redox titrations | For calculating the concentration of a solution in terms of moles of solute |
| Relationship | Molarity = Normality × Equivalent weight of solute | Normality = Molarity ÷ Equivalent weight of solute |