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What is a Mole in Chemistry?

A mole is the SI unit for the amount of substance, defined as the number of particles (atoms, molecules, or ions) equal to Avogadro's number (6.022 × 10²³). The mole concept is the bridge between the microscopic world (atoms, molecules) and the macroscopic world (grams, liters) that we measure in the laboratory. Moles are essential for stoichiometric calculations, solution concentration, and nearly all quantitative chemical calculations.

Mole Calculation Formula

n = m/Mr or n = V/22.4 (STP) or n = M × VFormula: n = number of particles / 6.022 × 10²³

Variables:

  • nNumber of moles (mol)
    Number of moles (mol)(e.g.: n = 2 mol)
  • mMass of substance (grams)
    Mass of substance (grams)(e.g.: m = 36 g)
  • MrMolar/relative mass (g/mol)
    Molar/relative mass (g/mol)(e.g.: Mr H₂O = 18 g/mol)
  • VVolume of gas at STP (liters)
    Volume of gas at STP (liters)(e.g.: V = 22.4 L)
  • MMolarity (mol/L)
    Molarity (mol/L)(e.g.: M = 1 M)

Categories:

From massn = m / Mr
From gas volumen = V / 22.4 L (STP)
From particlesn = N / 6.022×10²³
From solutionn = M × V

How to Use the KalkuLab Mole Calculator

  1. 1

    Select Calculation Method

    Choose from mass, gas volume, number of particles, or solution.

  2. 2

    Enter Data

    Enter known values (mass, molar mass, volume, etc.).

  3. 3

    Calculate

    The system calculates the number of moles automatically.

  4. 4

    View Results

    The mole count is displayed along with additional information.

Examples

Moles from Mass

Problem:

How many moles are in 36 grams of water (H₂O)?

Solution:
  1. 1.Mr H₂O = 2(1) + 16 = 18 g/mol
  2. 2.n = m/Mr = 36/18 = 2 mol
Result:2 mol

36 grams of water contains 2 moles, or 1.2 × 10²⁴ water molecules.

Gas Moles at STP

Problem:

How many moles are in 44.8 liters of O₂ gas at STP?

Solution:
  1. 1.At STP, 1 mol gas = 22.4 L
  2. 2.n = V/22.4 = 44.8/22.4 = 2 mol
Result:2 mol

44.8 liters of O₂ at STP = 2 mol = 64 grams.

Frequently Asked Questions

What is Avogadro's number?
Avogadro's number (Nₐ = 6.022 × 10²³) is the number of particles in 1 mole of a substance. It is named after Italian scientist Amedeo Avogadro.
Why is 22.4 L the molar volume?
At STP (0°C, 1 atm), 1 mole of an ideal gas occupies 22.4 liters. This is derived from the ideal gas law PV = nRT.
How do you calculate the molar mass of a compound?
Add the relative atomic masses of all atoms. Example: H₂SO₄ = 2(1) + 32 + 4(16) = 98 g/mol. Use the periodic table for relative atomic mass.

Related Calculators

Solution Concentration Calculator

Molarity and molality

Stoichiometry Calculator

Reaction calculations

Ideal Gas Calculator

PV = nRT

References