Equivalence mass, also known as gram equivalent or equivalent weight, is the mass of a substance that will combine with or displace a fixed quantity of another substance. In simpler terms, it's the amount of a substance that will react with or replace a specific amount of another substance in a chemical reaction.
Here's a breakdown of how equivalence mass works:
- For acids: Equivalence mass is the mass of acid that can donate one mole of hydrogen ions (H+). For example, the equivalence mass of HCl is its molar mass, as it has one replaceable hydrogen atom.
- For bases: Equivalence mass is the mass of base that can accept one mole of hydrogen ions (H+). For instance, the equivalence mass of NaOH is its molar mass because it has one replaceable hydroxide ion (OH-).
- For salts: Equivalence mass is the mass of salt that can produce one mole of positive or negative ions.
- For elements: The equivalence mass of an element is its atomic weight divided by its valence.
Examples:
- The equivalence mass of sulfuric acid (H2SO4) is half its molar mass because it can donate two moles of H+ ions.
- The equivalence mass of calcium hydroxide (Ca(OH)2) is half its molar mass because it can accept two moles of H+ ions.
Equivalence mass is a useful concept in stoichiometry, which is the study of the quantitative relationships between reactants and products in chemical reactions. It can be used to calculate the amount of one substance that will react with a given amount of another substance, or to determine the equivalent weight of a substance.
