Equivalent mass, also known as gram equivalent weight, represents the mass of a substance that will react with or combine with one mole of hydrogen ions (H+) or one mole of electrons. This concept is particularly important in stoichiometry, where it helps determine the relative amounts of reactants and products involved in a chemical reaction.
The equivalent mass of a substance depends on the specific reaction it participates in. For instance, in an acid-base reaction, the equivalent mass of an acid is its molecular mass divided by its basicity (number of replaceable hydrogen ions), while the equivalent mass of a base is its molecular mass divided by its acidity (number of replaceable hydroxide ions).
Here are some examples:
- For an acid: Equivalent mass of HCl = Molecular mass of HCl / 1 (basicity of HCl) = 36.5 g/mol / 1 = 36.5 g/equivalent.
- For a base: Equivalent mass of NaOH = Molecular mass of NaOH / 1 (acidity of NaOH) = 40 g/mol / 1 = 40 g/equivalent.
Equivalent mass is a useful concept for understanding the relative amounts of reactants and products in a reaction. However, it is essential to note that the concept of equivalent weight has been largely replaced by the more modern and consistent concept of molar mass.
