Gram equivalent weight of a salt:

The valence factor of a compound depends on the manner a compound is involved in a reaction. The compounds of alkali metal salts and alkaline earth metal salts are, however, constant. These compounds are ionic and they dissociate in ionic components in aqueous solution. In this case, valence factor is equal to numbers of electronic charge on either cation or anion.

Equivalent weight, E= Molecular weight of the compound/No. of electronic charge on the cation or anion

The numbers of electronic charge on cation of NaHCO₃ is 1. Hence, equivalent weight of NaHCO₃ is (23 + 1 + 12 + 3X16)/1 = 84.

Gram equivalent weight of an acid:

The valence factor of an acid is equal to its basicity. The basicity of an acid is equal to furnishable hydrogen ion (proton) in its aqueous solution. Importantly, basicity is not same as the number of hydrogen atoms in acid molecule. Consider acetic acid (CH3COOH). It contains 4 hydrogen atoms in it, but only 1 furnishable hydrogen ion. As such, basicity of acetic acid is 1. With this background, we define equivalent weight of an acid as :

Equivalent weight, E= Molecular weight of an acid/Basicity

For example, basicity of sulphuric acid is 2. Hence, equivalent weight of sulphuric acid (H₂SO₄) is (2X1 + 32 + 4X16)/2 = 98/2 = 49. Similarly, basicity of oxalic acid is 2. Hence, equivalent weight of oxalic acid (H₂C₂O₄ ) is (2X1 + 2X12 + 4X16)/2 = 90/2=45.