Mole (chemistry)
The mole is the SI base unit for the amount of substance, defined as exactly 6.02214076 × 10²³ elementary entities (atoms, molecules, ions, or other particles). It provides chemists with a practical bridge between the atomic scale and macroscopic, measurable quantities in the laboratory. One mole of any substance contains the same number of particles, making it the universal counting unit of chemistry.
Key Formula
n = N / N_A
LaTeX: n = \dfrac{N}{N_A}
| Symbol | Meaning | Unit |
|---|---|---|
| n | Amount of substance | mol |
| N | Number of elementary entities (atoms, molecules, etc.) | dimensionless |
| N_A | Avogadro's number (6.02214076 × 10²³) | mol⁻¹ |
Worked Example
Problem
How many moles are in 1.806 × 10²⁴ molecules of water (H₂O)?
Solution
Step 1: Use the definition: n = N / N_A. Step 2: Substitute values: n = (1.806 × 10²⁴) / (6.022 × 10²³). Step 3: Calculate: n = 3.00 mol.
Answer
3.00 mol of H₂O
Mole Relationships for Common Substances
| Substance | Molar Mass (g/mol) | 1 mol Mass (g) | Entities in 1 mol |
|---|---|---|---|
| H₂O (water) | 18.015 | 18.015 | 6.022 × 10²³ molecules |
| NaCl (table salt) | 58.44 | 58.44 | 6.022 × 10²³ formula units |
| C (carbon) | 12.011 | 12.011 | 6.022 × 10²³ atoms |
| Fe (iron) | 55.845 | 55.845 | 6.022 × 10²³ atoms |
| O₂ (oxygen gas) | 31.998 | 31.998 | 6.022 × 10²³ molecules |
Interactive Tools
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Related Terms
Avogadro's Number
Avogadro's number (N_A) is the defined numerical value 6.02214076 × 10²³ mol⁻¹, representing the number of constituent particles in one mole of a substance. Since the 2019 SI redefinition, it is an exact fixed constant rather than a measured value. It links the macroscopic world of grams and liters to the microscopic world of atoms and molecules, and is one of the most fundamental constants in all of science.
Molar Mass
Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol), and numerically equal to the substance's relative atomic or molecular mass in unified atomic mass units. It is calculated by summing the atomic masses of all atoms in one formula unit of the substance, using values from the periodic table. Molar mass is the essential conversion factor between grams (measurable in the lab) and moles (used in chemical calculations).
Stoichiometry
Stoichiometry is the branch of chemistry that deals with the quantitative relationships between reactants and products in chemical reactions. It uses balanced chemical equations to calculate the masses, volumes, or moles of substances involved in a reaction. Stoichiometry is fundamental to industrial chemistry, pharmaceutical manufacturing, and any process requiring precise control of chemical quantities.
From Latin "moles" meaning a large mass or pile. The term was introduced by Wilhelm Ostwald around 1896 as a convenient quantity for expressing amounts of substances at the atomic scale.