In chemistry, the equivalent concentration or normality (N) of a solution is defined as the molar concentration ci divided by an equivalence factor or n-factor feq:
There are three common types of chemical reaction where normality is used as a measure of reactive species in solution: Normal concentration of an ionic solution is also related to conductivity (electrolytic) through the use of equivalent conductivity.
Although losing favor in the medical industry, reporting of serum concentrations in units of "eq/L" (= 1 N) or "meq/L" (= 0.001 N) still occurs.
Since only 0.5 mol of H2SO4 are needed to neutralize 1 mol of OH−, the equivalence factor is: If the concentration of a sulfuric acid solution is c(H2SO4) = 1 mol/L, then its normality is 2 N. It can also be called a "2 normal" solution.
The normality of a solution depends on the equivalence factor feq for a particular reaction, which presents two possible sources of ambiguity – namely, feq depends on the choice of reaction as well as which chemical species of the reaction is being discussed (e.g., acid/base species, redox species, precipitating salts, isotopes exchanged, etc.).