# Molarity Study Guide

INTRODUCTION

Every system needs a measuring unit; for example, when your teacher asks you to draw a line of 5 units, you will ask her the scale to draw a line of 5 m or 5 cm or any other unit. Similarly, you will need to know the concentration of substances mixed with a solvent to get the desired solution. Hence, the invention of molarity took place. Source

### WHAT IS MOLARITY?

Molarity definition in chemistry refers to the number of moles present in a volume of solution in liters. Different elements react together in ratios of the whole number; their volume is expressed in moles. Molarity is the concentration unit and helps find out the concentration of different substances present in the solution.

### MOLARITY FORMULA

It is straightforward to find out the molarity; you need to know the solute’s moles and the solution’s volume. The formula of molarity is:

``                                    M = n / V``

Here,

M = the molality of the solution that is to be calculated

n = the number of moles of the solute

V = the volume of solution given in terms of liters Source

### EXAMPLE PROBLEMS

A solution is prepared by bubbling 2.56 grams of hydrochloric acid in water. Here, the volume of the solution is 46.8 mL. Calculate the molarity of the solution.

Solution:

The chemical formula of hydrochloric acid = HCl

The chemical formula for water = H₂O

The molecular weight of HCl = 35.5 × 1, 1 × 1 = 36.5 moles/gram

The molecular weight of H₂O = 1 × 2, 16 × 1 = 18 moles/gram

Given, the mass of hydrochloric acid in the solution = 2.56 g

The number of moles of hydrochloric acid = mass in gm / molecular weight = 2.56 / 36.5 = 7.02 x 10⁻² mole

Now, given the volume of the solution = 46.8 mL

Expressing the volume in terms of liters,

Volume = 46.8 / 1000 = 4.68 x 10⁻² L

∴ molarity of the substance = number of moles of elements/volume of the solution in liters = 7.02 x 10-2 / 4.68 x 10⁻² = 1.5 M

Ans: The molarity of the solution is 1.5 M

### FAQs:

1. What is a molar solution? Give an example.

Ans: The molar solution is the gram molecular weight of the solute used to calculate the molar concentration in liters of the solution. Hence, 1 molar solution (M) will contain 1.0 GMW of a substance dissolved in the solvent to make 1 liter of the solution. For example:The 1 M solution of NaCl will contain 58.44 g.

2. How do I calculate molarity?

Ans: To calculate the molarity of a solution, follow these simple steps:

Step 1: Find out the number of moles of solute present in the solution.

Step 2: Then, find out the volume of the solution in liters.

Step 3: Finally, divide the moles of solute with liters of solution, and you willget molarity.

3. What is the molarity of a solution?

Ans: The molarity of a solution can be defined as the moles of a solute per liter of the solution. In simple words, it is the amount of a substance present in a certain volume of a solution.

4. How is molarity used in everyday life?

Ans: The molarity is used to study the different properties of solutions when subjected to vapor pressure or temperature changes.

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## SOURCES:

1. Calculate Molarity of Solution: https://www.thoughtco.com/calculate-molarity-of-a-solution-606823. Accessed 28 Feb 2022.
2. What is Molarity? https://sciencetrends.com/what-is-molarity-with-examples/#:~:text=Molarity%20is%20how%20chemists%20measure,a%20given%20amount%20of%20solution. Accessed 28 Feb 2022.
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