The Mole Concept
- The number of particles that react in a chemical experiment cannot be directly determined because the size and mass of an individual particle is so small
- Moles are used to relate the mass of a sample to the number of particles it contains
- The mole (mol) is the SI unit for the amount of substance
- The number of moles (n) of a substance and the number of constituent particles or formula units it contains are related by Avogadro’s number (NA)
NA = 6.022 x 1023 mol-1
Number of constituent particles = NA x n
1 mole of… |
Fe atoms |
H2O molecules |
Al2(SO4)3 formula units |
Contains… |
6.022 x 1023 Fe atoms |
1.2044 x 1024 H atoms 6.022 x 1023 O atoms |
1.2044 x 1024 Al3+ ions 1.8066 x 1024 SO42- ions |
Exam Tip
Note that some textbooks will use the terms Avogadro’s constant and Avogadro’s number interchangeably.