Number of Moles Formula, Definition, Solved Examples

Number of Moles Formula: The concept of a mole is the fundamental measure of the amount of substance, serving as the cornerstone of stoichiometry. It represents the mass of a substance composed of a specific number of fundamental units, which can vary depending on the material and may be molecules, atoms, or formula units.

The quantity of moles in a substance is determined by the ratio of its given mass in a chemical reaction to the mass of one mole of that substance. One mole of any substance corresponds to Avogadro's number, precisely 6.023 × 10^23. It is also used to express concentration units, such as moles per liter or molecular weight. Before discussing the formula of calculating the number of moles, it's crucial to understand the mole concept.

Number of Moles

The mole concept proves highly valuable for quantifying the products in chemical reactions, particularly when dealing with substances at the molecular level. When we measure a molecule, we are essentially quantifying the significant number of atoms contained within that molecule. This is where the mole concept becomes essential. Given that one mole equals 6.023 × 10^23 atoms, it's evident that a mole is a substantial unit of measurement. One mole is equivalent to Avogadro's number. Let's now explore the process of determining the number of moles.

Number of Moles Formula

Number of Moles Formula. The number of moles of a substance is determined by the ratio of its specified mass in a chemical reaction to the mass of one mole of that substance. This ratio signifies how many moles can be derived from the given mass of the substance. In mathematical notation, this is represented as "n," and its standard unit of measurement is "mol." The mass of one mole of a substance is equivalent to its molar mass, which is calculated by summing the atomic weights of each element in the compound. Symbolically, the formula for the number of moles is expressed as follows:

The formula is as follows:

n = m/M

In this equation:

"n" represents the number of moles.

"m" signifies the mass of the substance.

"M" represents the mass of one mole of that substance.

Uses of Moles

The Mole Concept has several important applications. It serves as the cornerstone of stoichiometry, playing a crucial role in expressing the quantities of reactants and products in chemical reactions. Consequently, chemical reactions can be conveniently represented in terms of moles. For instance, let's consider the reaction involving carbonic acid reacting with potassium hydroxide to produce potassium carbonate and water.

Number of Moles Formula Solved Examples

Example 1: Calculate the quantity of moles present in 95 grams of MnO2.

Solution:

Given:

Mass of MnO2 = 95 grams

Molar mass of MnO2 = 86.94 grams/mole

Using the Number of Moles Formula:

Number of moles = Mass of the substance / Molar mass of one mole

Number of moles = 95 / 86.94

Number of moles = 1.092 moles

Example 2: Calculate the number of moles in 25 grams of water (H2O).

Solution:

Given:

Mass of H2O = 25 grams

Molar mass of H2O = 18.015 grams/mole

Number of Moles Formula = Mass of the substance / Molar mass of one mole

Number of moles = 25 / 18.015

Number of moles ≈ 1.387 moles

Example 3: Determine the moles of carbon dioxide (CO2) in a 50-gram sample.

Solution:

Given:

Mass of CO2 = 50 grams

Molar mass of CO2 = 44.01 grams/mole

Number of Moles Formula = Mass of the substance / Molar mass of one mole

Number of moles = 50 / 44.01

Number of moles ≈ 1.136 moles

Example 4: Find the number of moles in 10 grams of methane (CH4).

Solution:

Given:

Mass of CH4 = 10 grams

Molar mass of CH4 = 16.04 grams/mole

Number of Moles Formula = Mass of the substance / Molar mass of one mole

Number of moles = 10 / 16.04

Number of moles ≈ 0.624 mole.

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