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

Definition

Normality is defined as the number of gram or mole equivalents of solute present in one liter of solution. The SI unit of normality is equivalents per liter (Eq/L). where N is normality, msol is the mass of solute in grams, EWsol is the equivalent weight of solute, and Vsoln is the volume of the entire solution in liters.

Usage

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.

Medical

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.

Examples

Normality can be used for acid-base titrations. For example, sulfuric acid (H2SO4) is a diprotic acid. 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. Similarly, for a solution with c(H3PO4) = 1 mol/L, the normality is 3 N because phosphoric acid contains 3 acidic H atoms.

Criticism of the term "normality"

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.). That is to say, the same solution can possess different normalities for different reactions or potentially even the same reaction in a different context. To avoid ambiguity, IUPAC and NIST discourage the use of the terms "normality" and "normal solution".