Molarity – Formula, Definition, and Examples


In our day-to-day life, we often encounter substances that are mixtures of different elements and compounds. Further, one such example of a mixture is the human body. We are actually an assortment of biological molecules, gases, and inorganic ions dissolved in water.  Molarity Formula will help you understand it better.

In the homogeneous mixtures, substances are mixed together in such a way that the composition will be the same throughout the sample. On the other hand, the heterogeneous mixture does not have a uniform composition throughout the sample.

Moreover, in this topic, the student will learn about solutions. Also, they will learn molarity of such a solution with molarity formula with examples.

What are Solutions?

Homogeneous mixtures are also termed as solutions, and these solutions can contain components that are solids, liquids and/or gases.

Thus, often we want to be able to quantify the amount of a species that is present in the solution. This quantity is the concentration of that species.

Many of such information is useful in doing stoichiometric calculations.

molarity formula

What is Molar concentration?

The component of a solution which is present in the largest amount is known as the solvent. Also, any chemical species mixed in the solvent is called a solute.

Here solutes can be gases, liquids, or solids. Further, the molarity or molar concentration of a solute is an important property.

The molar concentration of the solute is sometimes abbreviated by using square brackets around the chemical formula of the solute. Further, molar concentration allows us to convert between the volume of the solution and the moles of the solute.

The accuracy of our molar concentration will depend on our choice of glassware and the accuracy of the balance we use to measure out the solute. Similarly, the use of the glassware to determine the accuracy of our solution volume.

Definition of Molarity

Now, we will see the specific definition of Molarity of a given solution. We define it as the total number of moles of solute per litre of solution. Moreover, it depends on the changes in the physical properties of the system like pressure and temperature.

This is because of the fact that unlike mass, the volume of the system changes with the change in the physical conditions of the system. Thus, the unit of molarity is termed as Molar.

One molar is the molarity of a solution where one gram of solute dissolves in a litre of solution. Since in a solution, the solvent and solute blend to make a solution. Therefore, we take the total volume of the solution.

Molarity Formula With Example

The equation to calculate molarity is the ratio of the moles of solute. Ones whose molarity we need to calculate and the volume of solvent we use to dissolve the given solute.


Here, M = molarity of the solution

n = number of moles of the solute and

V = volume of solution given in terms of litres.

Example: What is the molarity of a solution prepared by dissolving 13.2 g of NaCl insufficient water to give 2.00 litres?

Solution: First, determine the number of moles of NaCl in 13.2 g.

Number of moles = weight in gram /molar mass

= 13.2/58.5 = 0.23 moles

Now, calculate molar mass of NaCl which is 23 + 35.5 = 58.5 g/mol


Molarity = number of moles/volume (litre) = 0.23/2 = 0.115

Solved Question for you

Q: What volume of 2.00 M NaOH we need to furnish 12.0 g of NaOH for a reaction?

Ans: First convert 12.0 g of NaOH to number of moles as:

Number of moles = weight in gram / molar mass

Since molar mass of NaOH = 23 + 16 + 1 = 40 g / mol

So, Number of moles of NaOH = 12/40 = 0.30

Now, Molarity = number of moles/volume (in liter)

i.e. Volume = number of moles / Molarity

Hence Volume = 0.3/2.0 = 0.15 liter

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