Molecular Mass and Mole Concept

Molecular Mass and Mole Concept

•  Molecular Mass

      It is the sum of the atomic masses of all the atoms in a molecule of the substance. It is expressed in atomic mass unit (u).

      e.g., 2H+ + O2 H2O [H = 1, 0 = 16]

      1 × 2 + 16 = 18 u

•  Formula Unit Mass

      It is the sum of the atomic masses of all atoms in a formula unit of a compound. The constituent particles are ions.

      e.g., Na+ + Cl → NaCl

      1 × 23 + 1 × 35.5 = 58.5 u

•  Mole Concept

      Definition of mole: It is defined as one mole of any species (atom, molecules, ions or particles) is that quantity in number having a mass equal to its atomic or molecular mass in grams.

                  1 mole = 6.022 × 1023 in number

      Molar mass = mass of 1 mole → is is always expressed in r gram, and is also known as gram atomic mass.

      1u of hydrogen has → 1 atom of hydrogen

      lg of hydrogen has → 1 mole of hydrogen

      = 6.022 × 1023 atoms of hydrogens