# What are equivalnts and milliequivalents?

Jul 4, 2017

Equivalents are the mols of ions multiplied by their valency... and that's what makes this tricky and thus, outdated and generally discouraged for active usage.

Milliequivalents are analogous and 1000 times smaller in magnitude, i.e. there are 1000 milliequivalents, or $\text{mEq}$, in one equivalent.

A very old term that relates to normality concentrations... The most "modern" definition has that...

• For acid-base chemistry, it is the amount of substance needed to react with or to supply $\boldsymbol{\text{1 mol}}$ of $\boldsymbol{{\text{H}}^{+}}$.
• For redox reactions, it pertains to the amount of substance needed to react with or to supply $\boldsymbol{\text{1 mol}}$ of electrons.

For example,

• In ${\text{CaCl}}_{2}$, you have two equivalents of ${\text{Cl}}^{-}$ (which is fine), but two (not one!) equivalents of ${\text{Ca}}^{2 +}$, simply because one equivalent accepts one electron, and ${\text{Ca}}^{2 +}$ can accept two electrons...
• In ${\text{FeCl}}_{3}$, you have three of ${\text{Cl}}^{-}$ (which is normal), but three equivalents of ${\text{Fe}}^{3 +}$ (not one!).

In short, it is the mols of ions multiplied by their valency... and that's what makes this tricky and thus, outdated and generally discouraged for active usage.

NOTE: It DOES find its uses however, in determination of an unknown acid, for instance. One can only calculate its equivalent weight, and then multiply by either $2$ or $3$ with the forethought that the acid might be diprotic or triprotic, respectively.