chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...

, the equivalent concentration or normality () of a solution is defined as the

molar concentration Molar concentration (also called molarity, amount concentration or substance concentration) is the number of moles of solute per liter of solution. Specifically, It is a measure of the concentration of a chemical species, in particular, of a so ...

divided by an equivalence factor or -factor :

N = \frac

Definition

Normality is defined as the number of

gram The gram (originally gramme; SI unit symbol g) is a Physical unit, unit of mass in the International System of Units (SI) equal to one thousandth of a kilogram. Originally defined in 1795 as "the absolute Mass versus weight, weight of a volume ...

or mole equivalents of

solute In chemistry, a solution is defined by IUPAC as "A liquid or solid phase containing more than one substance, when for convenience one (or more) substance, which is called the solvent, is treated differently from the other substances, which are ...

present in one liter of solution. The

SI unit The International System of Units, internationally known by the abbreviation SI (from French ), is the modern form of the metric system and the world's most widely used system of units of measurement, system of measurement. It is the only system ...

of normality is equivalents per liter (Eq/L).

N = \frac

where is normality, is the

mass Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...

of solute in grams, is the equivalent weight of solute, and is the

volume Volume is a measure of regions in three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch) ...

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: *In acid-base chemistry, normality is used to express the concentration of

hydronium In chemistry, hydronium (hydroxonium in traditional British English) is the cation , also written as , the type of oxonium ion produced by protonation of water. It is often viewed as the positive ion present when an Arrhenius acid is dissolved ...

ions (H₃O⁺) or hydroxide ions (OH⁻) in a solution. Here, is an

integer An integer is the number zero (0), a positive natural number (1, 2, 3, ...), or the negation of a positive natural number (−1, −2, −3, ...). The negations or additive inverses of the positive natural numbers are referred to as negative in ...

value. Each solute can produce one or more equivalents of reactive species when dissolved. *In

redox Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is t ...

reactions, the equivalence factor describes the number of

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

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 from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...

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 env ...

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 Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

(H₂SO₄) is a

diprotic acid An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen cation, H+), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis acid. The first category of acids are the ...

. Since only 0.5 mol of H₂SO₄ are needed to neutralize 1 mol of OH⁻, the equivalence factor is: :''f''_eq(H₂SO₄) = 0.5 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 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, ...

contains 3 acidic H atoms.

Criticism of the term "normality"

The normality of a solution depends on the equivalence factor _eq for a particular reaction, which presents two possible sources of ambiguity – namely, _eq depends on the choice of reaction as well as which

chemical species Chemical species are a specific form of chemical substance or chemically identical molecular entities that have the same molecular energy level at a specified timescale. These entities are classified through bonding types and relative abundance of ...

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 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 ...

Archived
(PDF) from the original on July 26, 2011. Retrieved 2009-05-10. 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 s ...

discourage the use of the terms "normality" and "normal solution".

References

External links

Analytical Chemistry 2.1, by David Harvey (Open-source Textboox) , Chapter 16.1: Normality
* ''Normality: Definition, formula, equations, type, example'',. {{analytical-chem-stub Concentration