Equivalent mass of an acid is the number of parts by mass of the acids which contains 1.008 parts by mass of replaceable hydrogen.
The equivalent mass of the acid is equal to the number of grams of an acid per mole of available H+ ion:
One equivalent mass of an acid ----- one mole H+ ion
In all cases the molar mass and the equivalent mass are related by simple equations, but in order to find the molar mass from the equivalent mass we need to know the molecular formula of the acid.
Equivalent Mass is the amount of substance that combines with or displaces 8.0 g of oxygen (or 1.008 g of hydrogen), usually expressed in grams; for acid/base reactions, one equivalent donates or receives a mole of protons and the equivalent weight is the ratio of the molecular weight to the number of protons involved in the reaction. For oxidation-reduction reactions, one equivalent donates or receives a mole of electrons and the equivalent weight is the ratio of the molecular weight to the number of electrons involved in the reaction.
Calculate the Equivalent mass of an acid (EM).
Molecular Mass of an Acid: 25
Number of ionizable hydrogens (H+): 10
Equivalent mass of an acid (EM): 2.5 (g/mol H+)
Equivalent Mass = (Molecular mass of acid) / (number of ionizable hydrogens)