Molarity Formula: Definition And Solved Examples

Molarity Formula : Chemistry is a fascinating field that seeks to unravel the mysteries of matter and its interactions. One of the fundamental concepts in chemistry is molarity, a measure of the concentration of a solution. Whether you’re a student just starting your chemistry journey or a seasoned scientist, understanding the molarity formula and its applications is crucial. Within this article, we aim to explore the concept of molarity, its mathematical formula, and offer solved examples to aid your understanding of this fundamental subject.

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What is Molarity?

Molarity, often denoted as “M,” is a unit of concentration used in chemistry to express the number of moles of a solute present in one liter of solution. It is a way to quantify how much of a substance is dissolved in a given volume of solvent. Molarity is an essential concept in various chemical calculations, such as dilutions, stoichiometry, and reaction rate analysis.

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The Molarity Formula

The molarity of a solution can be calculated using the following formula:

Molarity (M) = Moles of Solute (n) / Volume of Solution (V in liters)

Mathematically, this can be represented as:

M = n / V

Where:

M represents molarity (in moles per liter, mol/L or M).

n stands for the number of moles of the solute.

V is the volume of the solution in liters (L).

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Application of Molarity

Molarity (M) is a key concept in chemistry used to measure the concentration of solutes in solutions. Its applications span various fields, including chemical reactions, analytical chemistry, pharmaceuticals, environmental science, biology, industry, education, and research. Molarity enables precise measurements, accurate dosing, and quality control in a wide range of scientific and industrial processes.

Molarity Formula Solved Examples

Solved Example 1: Calculating Molarity

Let’s work through a simple example to illustrate how to use the molarity formula:

Example: You have 0.25 moles of sodium chloride (NaCl) dissolved in 500 milliliters (0.5 liters) of water. What is the molarity of the NaCl solution?

Solution:

First, convert the volume of the solution to liters: V = 0.5 L.

Next, calculate the molarity using the formula:

M = n / V

M = 0.25 moles / 0.5 L

Now, perform the calculation:

M = 0.5 M

So, the molarity of the NaCl solution is 0.5 moles per liter or 0.5 M.

Solved Example 2: Dilution

Dilution is a common laboratory technique used to prepare solutions of lower concentration from a stock solution of higher concentration. Let’s consider a dilution example:

Example: You have a stock solution of hydrochloric acid (HCl) with a molarity of 6 M. How many milliliters of the stock solution must be diluted to prepare 250 mL of a 2 M HCl solution?

Solution:

First, rearrange the molarity formula to find the volume (V) needed for the diluted solution:

V1 * M1 = V2 * M2

Where:

V1 is the volume of the stock solution (unknown).

M1 is the molarity of the stock solution (6 M).

V2 represents the volume of the diluted solution, which can be either 250 milliliters or 0.25 liters.

M2 is the desired molarity (2 M).

Plug in the values and solve for V1:

V1 * 6 M = 0.25 L * 2 M

V1 = (0.25 L * 2 M) / 6 M

Calculate the volume of the stock solution required:

V1 = 0.0833 L (or 83.3 mL)

So, you need to dilute 83.3 mL of the 6 M HCl solution to prepare 250 mL of a 2 M HCl solution.

Understanding molarity is essential for various aspects of chemistry, from preparing solutions to performing chemical reactions. The molarity formula, M = n / V, is a valuable tool for quantifying the concentration of solutes in solutions. By applying this formula, you can calculate molarity and solve various chemical problems, including dilutions and stoichiometry calculations. With practice and a solid grasp of molarity, you will be better equipped to tackle more complex chemistry concepts and experiments.