In
chemistry, the equivalent concentration or normality (N) of a
solution
Solution may refer to:
* Solution (chemistry), a mixture where one substance is dissolved in another
* Solution (equation), in mathematics
** Numerical solution, in numerical analysis, approximate solutions within specified error bounds
* Solutio ...
is defined as the
molar concentration ''c
i'' divided by an equivalence factor ''f''
eq:
:Normality =
Definition
Normality is defined as the number of gramme or mole
equivalents
''Equivalents'' is a series of photographs of clouds taken by Alfred Stieglitz from 1925 to 1934. They are generally recognized as the first photographs intended to free the subject matter from literal interpretation, and, as such, are some of t ...
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 is d ...
ions (H
3O
+) or hydroxide ions (OH
−) in a solution. Here, is an
integer value. Each solute can produce one or more equivalents of reactive species when dissolved.
*In
redox reactions, the equivalence factor describes the number of
electrons that an oxidizing or reducing agent can accept or donate. Here, can have a fractional (non-integer) value.
*In
precipitation 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)
Conductivity (or specific conductance) of an electrolyte solution is a measure of its ability to conduct electricity. The SI unit of conductivity is Siemens per meter (S/m).
Conductivity measurements are used routinely in many industrial and e ...
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. 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 contains 3 acidic H atoms.
Criticism of the term "normality"
Normality is an ambiguous measure of the
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
''Equivalents'' is a series of photographs of clouds taken by Alfred Stieglitz from 1925 to 1934. They are generally recognized as the first photographs intended to free the subject matter from literal interpretation, and, as such, are some of t ...
). 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
The National Institute of Standards and Technology (NIST) is an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into physical sc ...
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
Saline (also known as saline solution) is a mixture of sodium chloride (salt) and water. It has a number of uses in medicine including cleaning wounds, removal and storage of contact lenses, and help with dry eyes. By injection into a vein ...
, 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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