![Na+H2O](https://upload.wikimedia.org/wikipedia/commons/6/67/Na%2BH2O.svg)
An aqueous solution is 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
* Soluti ...
in which the
solvent
A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
is
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
. It is mostly shown in
chemical equation
A chemical equation is the symbolic representation of a chemical reaction in the form of symbols and chemical formulas. The reactant entities are given on the left-hand side and the product entities on the right-hand side with a plus sign between ...
s by appending (aq) to the relevant
chemical formula
In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...
. For example, a solution of
table salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...
, or
sodium chloride
Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...
(NaCl), in water would be represented as . The word ''aqueous'' (which comes from ''aqua'') means pertaining to, related to, similar to, or
dissolved in, water.
As water is an excellent solvent and is also naturally abundant, it is a ubiquitous solvent in
chemistry
Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...
. Since water is frequently used as the solvent in experiments, the word solution refers to an aqueous solution, unless the solvent is specified.
A ''non-aqueous solution'' is a solution in which the solvent is a liquid, but is not water.
(See also
Solvent
A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
and
Inorganic nonaqueous solvent
An inorganic nonaqueous solvent is a solvent other than water, that is not an organic compound. These solvents are used in chemical research and industry for reactions that cannot occur in aqueous solutions or require a special environment. Inorgan ...
.)
Characteristics
Substances that are ''
hydrophobic
In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water.
Hydrophobic molecules tend to be nonpolar and, th ...
'' ('water-fearing') do not dissolve well in water, whereas those that are ''
hydrophilic
A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water.Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon'' Oxford: Clarendon Press.
In contrast, hydrophobes are no ...
'' ('water-friendly') do. An example of a hydrophilic substance is sodium chloride. In an aqueous solution the hydrogen ions () and hydroxide ions () are in
Arrhenius balance ( = ''
Kw'' = 1 x 10
−14 at 298 K).
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 ...
s and
bases are aqueous solutions, as part of their
Arrhenius definitions.
An example of an Arrhenius acid is
hydrogen chloride
The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride ga ...
(HCl) because of its dissociation of the hydrogen ion when dissolved in water.
Sodium hydroxide
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly caustic base and alkali ...
(NaOH) is an Arrhenius base because it dissociates the hydroxide ion when it is dissolved in water.
Aqueous solutions may contain, especially in the alkaline zone or subjected to radiolysis, hydrated atomic hydrogen and
hydrated electron
A solvated electron is a free electron in (solvated in) a solution, and is the smallest possible anion. Solvated electrons occur widely. Often, discussions of solvated electrons focus on their solutions in ammonia, which are stable for days, but s ...
s.
Electrolytes
Aqueous solutions that conduct
electric current
An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving pa ...
efficiently contain strong
electrolyte
An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon dis ...
s, while ones that conduct poorly are considered to have weak electrolytes. Those strong electrolytes are substances that are completely
ionized
Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule ...
in water, whereas the weak electrolytes exhibit only a small degree of ionization in water.
The ability for ions to move freely through the solvent is a characteristic of an aqueous strong electrolyte solution. The solutes in a weak electrolyte solution are present as ions, but only in a small amount.
Nonelectrolytes are substances that dissolve in water yet maintain their molecular integrity (do not dissociate into ions). Examples include
sugar
Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or double ...
,
urea
Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid.
Urea serves an important r ...
,
glycerol
Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
, and
methylsulfonylmethane
Methylsulfonylmethane (MSM) is an organosulfur compound with the formula (CH3)2SO2. It is also known by several other names including methyl sulfone and dimethyl sulfone (DMSO2). This colorless solid features the sulfonyl functional group and is t ...
(MSM).
Reactions
Reactions in aqueous solutions are usually
metathesis reactions. Metathesis reactions are another term for
double-displacement
A salt metathesis reaction, sometimes called a double displacement reaction, is a chemical process involving the exchange of bonds between two reacting chemical species which results in the creation of products with similar or identical bonding a ...
; that is, when a cation displaces to form an ionic bond with the other anion. The cation bonded with the latter anion will dissociate and bond with the other anion.
A common metathesis reaction in aqueous solutions is a
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. ...
reaction. This reaction occurs when two aqueous strong electrolyte solutions mix and produce an insoluble solid, also known as a
precipitate
In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...
. The ability of a substance to dissolve in water is determined by whether the substance can match or exceed the strong
attractive forces that water molecules generate between themselves. If the substance lacks the ability to dissolve in water, the molecules form a
precipitate
In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...
.
When writing the equations of precipitation reactions, it is essential to determine the precipitate. To determine the precipitate, one must consult a
chart of solubility. Soluble compounds are aqueous, while insoluble compounds are the precipitate. There may not always be a precipitate. Complete
ionic equation
A chemical equation is the symbolic representation of a chemical reaction in the form of symbols and chemical formulas. The reactant entities are given on the left-hand side and the product entities on the right-hand side with a plus sign between t ...
s and net ionic equations are used to show dissociated ions in metathesis reactions. When performing calculations regarding the
reacting of one or more aqueous solutions, in general one must know 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'', an ...
, or
molarity
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 solut ...
, of the aqueous solutions.
See also
*
Acid–base reaction
An acid–base reaction is a chemical reaction that occurs between an acid and a base. It can be used to determine pH via titration. Several theoretical frameworks provide alternative conceptions of the reaction mechanisms and their applica ...
*
Acidity function
*
Dissociation (chemistry)
Dissociation in chemistry is a general process in which molecules (or ionic compounds such as salts, or complexes) separate or split into other things such as atoms, ions, or radicals, usually in a reversible manner. For instance, when an acid ...
*
List of ions in pure water (aqueous chemistry)
This table lists the ionic species that are most likely to be present, depending on pH, in aqueous solutions of binary salts of metal ions. The existence must be inferred on the basis of indirect evidence provided by modelling with experimental da ...
*
Metal ions in aqueous solution
A metal ion in aqueous solution or aqua ion is a cation, dissolved in water, of chemical formula (H2O)nsup>z+. The solvation number, ''n'', determined by a variety of experimental methods is 4 for Li+ and Be2+ and 6 for most elements in periods 3 ...
*
Properties of water
Water () is a polar inorganic compound that is at room temperature a tasteless and odorless liquid, which is nearly colorless apart from an inherent hint of blue. It is by far the most studied chemical compound and is described as the "univer ...
*
Solubility
In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution.
The extent of the solubil ...
*
Solvated electron
A solvated electron is a free electron in (solvated in) a solution, and is the smallest possible anion. Solvated electrons occur widely. Often, discussions of solvated electrons focus on their solutions in ammonia, which are stable for days, but s ...
References
*
{{Chemical solutions
Chemical properties
Solutions