What unit is used to measure the amount of substance in chemistry?

The mole (mol) is the fundamental unit used to measure the amount of substance in chemistry. It defines the quantity of particles, such as atoms or molecules, in a given sample. One mole of any substance contains the same number of entities as there are atoms in 12 grams of carbon-12, which is approximately (6.022 \times 10^{23}) particles, a number known as Avogadro's number. This unit allows chemists to convert between the mass of a substance and the number of particles, enabling calculations necessary for stoichiometry, reactions, and various other chemical manipulations.

In contrast, the gram is a unit of mass, liters measure volume, and meters are used for length. While these units can be related to substance quantity in specific contexts (for example, grams can relate to moles through molar mass), they are not the primary unit for the amount of substance itself. The mole is uniquely designed for this purpose, making it essential for understanding and performing chemical reactions and calculations.