Subsection 8.4.2 The Mole
Mole is a unit used to measure the amount of a substance. One mole of a substance is defined as the amount of substance that contains the same number of particles (atoms, molecules, or ions) as there are in 12 grams of carbon-12. This number is known as Avogadro’s number, N_o and is approximately \(6.022 \times 10^{23} \) particles per mole. For example, one mole of water \((H_2O) \) contains \(6.022 \times 10^{23} \) water molecules, while one mole of sodium chloride \((NaCl)\) contains \(6.022 \times 10^{23} \) sodium ions and \(6.022 \times 10^{23} \) chloride ions. The mole is a convenient unit for chemists because it allows them to compare the amounts of different substances on the basis of the number of particles they contain, rather than their mass or volume. The number of atoms or molecules or anything in 1 mole of any substance is always the same as Avogadro’s number.
Atomic mass unit (amu) is a unit of mass used to express the relative masses of atoms and molecules. It is defined as one twelfth (1/12) of the mass of a carbon-12 atom, which is assigned a mass of exactly 12 amu. This means that the mass of one proton or one neutron is approximately 1 amu, and the mass of an electron is much smaller, about 0.0005 amu. The atomic mass of an element, which is the weighted average of the masses of its isotopes, is expressed in amu. The use of atomic mass units is convenient because it allows us to compare the masses of different atoms and molecules on a relative scale. For example, the mass of a hydrogen atom is about 1 amu, while the mass of an oxygen atom is about 16 amu.
Molar mass is the mass of one mole of a substance, typically expressed in units of grams per mole (g/mol). It is calculated by summing the atomic masses of all the atoms in a molecule or formula unit of a compound. The molar mass is an important concept in chemistry as it is used to convert between the mass of a substance and the number of moles of that substance. It is also used in stoichiometric calculations to determine the quantities of reactants and products in chemical reactions.