In
chemistry, the equivalent concentration or normality (N) of a
solution is defined as the
molar concentration
Molar concentration (also called molarity, amount concentration or substance concentration) is a measure of the concentration of a chemical species, in particular of a solute in a solution, in terms of amount of substance per unit volume of sol ...
''c
i'' divided by an equivalence factor ''f''
eq:
:Normality =
Definition
Normality is defined as the number of gramme or mole
equivalents of solute present in one litre of solution. The SI unit of normality is Eq/L.
Normality formula
:Normality (N) = Weight of Solute (in gm) / (Equivalent Weight of Solute × Volume of the Solution (in liters))
[https://clavick.com/normality/]
Usage
There are three common types of chemical reaction where normality is used as a measure of reactive species in solution:
*In
acid-base chemistry, normality is used to express the concentration of
hydronium
In chemistry, hydronium (hydroxonium in traditional British English) is the common name for the aqueous cation , the type of oxonium ion produced by protonation of water. It is often viewed as the positive ion present when an Arrhenius acid i ...
ions (H
3O
+) or hydroxide ions (OH
−) in a solution. Here, is an
integer
An integer is the number zero (), a positive natural number (, , , etc.) or a negative integer with a minus sign ( −1, −2, −3, etc.). The negative numbers are the additive inverses of the corresponding positive numbers. In the languag ...
value. Each solute can produce one or more equivalents of reactive species when dissolved.
*In
redox
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
reactions, the equivalence factor describes the number of
electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no ...
s that an oxidizing or reducing agent can accept or donate. Here, can have a fractional (non-integer) value.
*In
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
reactions, the equivalence factor measures the number of ions which will precipitate in a given reaction. Here, is an integer value.
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 (H
2SO
4) is a
diprotic acid
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
. Since only 0.5 mol of H
2SO
4 are needed to neutralize 1 mol of OH
−, the equivalence factor is:
:''f''
eq(H
2SO
4) = 0.5
If the concentration of a sulfuric acid solution is ''c''(H
2SO
4) = 1 mol/L, then its normality is 2 N. It can also be called a "2 normal" solution.
Similarly, for a solution with ''c''(H
3PO
4) = 1 mol/L, the normality is 3 N because
phosphoric acid
Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solution, w ...
contains 3 acidic H atoms.
Criticism of the term "normality"
Normality is an ambiguous measure of the
concentration
In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', ''molar concentration'', '' number concentration'', ...
of a given
reagent in solution. It needs a definition of the equivalence factor, which depends on the definition of the reaction unit (and therefore
equivalents). The same solution can possess ''different'' normalities for ''different'' reactions. The definition of the equivalence factor varies depending on the type of chemical reaction that is discussed: It may refer to equations, bases, redox species, precipitating ions, or isotopes. Since a reagent solution with a definite concentration may have different normality depending on which reaction is considered,
IUPAC
The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
and
NIST discourage the use of the terms "normality" and "normal solution".
[ ]
See also
*
Equivalent (chemistry)
An equivalent (symbol: officially equiv; unofficially but often Eq) is the amount of a substance that reacts with (or is ''equivalent'' to) an arbitrary amount (typically one mole) of another substance in a given chemical reaction. It is an arch ...
*
Normal saline, a solution of NaCl, but not a normal solution. Its normality is about 0.154 N.
References
External Links
Normality , Definition, Formula, Equations with Examples. ClaVick.Analytical Chemistry 2.1, by David Harvey (Open-source Textboox) , Chapter 16.1: Normality
Analytical chemistry
Chemical properties
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