Inchemistry, theequivalent concentration ornormality (N) of asolution is defined as themolar concentrationci divided by anequivalence factor orn-factorfeq:
Normality is defined as the number ofgram ormoleequivalents ofsolute present in one liter ofsolution. TheSI unit of normality is equivalents perliter (Eq/L).
whereN is normality,msol is themass of solute in grams,EWsol is theequivalent weight of solute, andVsoln is thevolume of the entire solution in liters.
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 toconductivity (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.
Normality can be used foracid-base titrations. For example,sulfuric acid (H2SO4) is adiprotic 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 isc(H2SO4) = 1 mol/L, then its normality is 2 N. It can also be called a "2 normal" solution.
Similarly, for a solution withc(H3PO4) = 1 mol/L, the normality is 3 N becausephosphoric acid contains 3 acidic H atoms.
The normality of a solution depends on the equivalence factorfeq for a particular reaction, which presents two possible sources of ambiguity – namely,feq depends on the choice of reaction as well as whichchemical 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[1] andNIST[2] discourage the use of the terms "normality" and "normal solution".
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