Aqueous solution

An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be represented as Na+(aq) + Cl(aq). The word aqueous (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. Aqueous solution is water with a pH of 7.0 where the hydrogen ions (H+) and hydroxide ions (OH) are in Arrhenius balance (10−7).

A non-aqueous solution is a solution in which the solvent is a liquid, but is not water.[1]

Substances that are hydrophobic ('water-fearing') often do not dissolve well in water, whereas those that are hydrophilic ('water-friendly') do. An example of a hydrophilic substance is sodium chloride. Acids and bases are aqueous solutions, as part of their Arrhenius definitions.

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.

Reactions in aqueous solutions are usually metathesis reactions. Metathesis reactions are another term for double-displacement; 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.

Aqueous solutions that conduct electric current efficiently contain strong electrolytes, while ones that conduct poorly are considered to have weak electrolytes. Those strong electrolytes are substances that are completely ionized in water, whereas the weak electrolytes exhibit only a small degree of ionization in water.

Nonelectrolytes are substances that dissolve in water yet maintain their molecular integrity (do not dissociate into ions). Examples include sugar, urea, glycerol, and methylsulfonylmethane (MSM).

When writing the equations of aqueous 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.

When performing calculations regarding the reacting of one or more aqueous solutions, in general one must know the concentration, or molarity, of the aqueous solutions. Solution concentration is given in terms of the form of the solute prior to it dissolving.

Aqueous solutions may contain, especially in alcaline zone or subjected to radiolysis, hydrated atomic hydrogen an hydrated electron.

The first solvation shell of a sodium ion dissolved in water.

See also


  1. ^ "Solutions". Washington University Chemistry Department. Washington University. Retrieved 13 April 2018.

Aluminon, the triammonium salt of aurintricarboxylic acid, is a dye often used to detect the presence of the aluminium ion in an aqueous solution. Aluminon forms a red complex salt in combination with Al3+.

In addition to its use in qualitative inorganic analysis, aluminon has applications in pigment production. It forms brilliantly colored lake pigments with many metals. The pigments are red in combination with Be2+ and Ga3+. The pigment is deep purple or reddish-brown in combination with Fe3+. Color of a particular pigment in acidic solutions may change: aluminon and Sc2+ form red pigments if the solution is acidic, but otherwise the solutions are colorless.Aluminon is prepared by reacting sodium nitrite with salicylic acid, adding formaldehyde, then treating with ammonia.

Base (chemistry)

In chemistry, bases are substances that, in aqueous solution, release hydroxide (OH−) ions, are slippery to the touch, can taste bitter if an alkali, change the color of indicators (e.g., turn red litmus paper blue), react with acids to form salts, promote certain chemical reactions (base catalysis), accept protons from any proton donor or contain completely or partially displaceable OH− ions. Examples of bases are the hydroxides of the alkali metals and the alkaline earth metals (NaOH, Ca(OH)2, etc.—see alkali hydroxide and alkaline earth hydroxide).

In water, by altering the autoionization equilibrium, bases yield solutions in which the hydrogen ion activity is lower than it is in pure water, i.e., the water has a pH higher than 7.0 at standard conditions. A soluble base is called an alkali if it contains and releases OH− ions quantitatively. However, it is important to realize that basicity is not the same as alkalinity. Metal oxides, hydroxides, and especially alkoxides are basic, and conjugate bases of weak acids are weak bases.

Bases can be thought of as the chemical opposite of acids. However, some strong acids are able to act as bases. Bases and acids are seen as opposites because the effect of an acid is to increase the hydronium (H3O+) concentration in water, whereas bases reduce this concentration. A reaction between an acid and a base is called neutralization. In a neutralization reaction, an aqueous solution of a base reacts with an aqueous solution of an acid to produce a solution of water and salt in which the salt separates into its component ions. If the aqueous solution is saturated with a given salt solute, any additional such salt precipitates out of the solution.

For a substance to be classified as an Arrhenius base, it must produce hydroxide ions in an aqueous solution. Arrhenius believed that in order to do so, the base must contain hydroxide in the formula. This makes the Arrhenius model limited, as it cannot explain the basic properties of aqueous solutions of ammonia (NH3) or its organic derivatives (amines). There are also bases that do not contain a hydroxide ion but nevertheless react with water, resulting in an increase in the concentration of the hydroxide ion. An example of this is the reaction between ammonia and water to produce ammonium and hydroxide. In this reaction ammonia is the base because it accepts a proton from the water molecule. Ammonia and other bases similar to it usually have the ability to form a bond with a proton due to the unshared pair of electrons that they possess. In the more general Brønsted–Lowry acid–base theory, a base is a substance that can accept hydrogen cations (H+)—otherwise known as protons. In the Lewis model, a base is an electron pair donor.

Cobalt(III) oxide

Cobalt (III) oxide is the inorganic compound with the formula of Co2O3. Although only two oxides of cobalt are well characterized, CoO and Co3O4, procedures claiming to give Co2O3 have been described. Thus treatment of Co(II) salts such as cobalt(II) nitrate with an aqueous solution of sodium hypochlorite (also known as bleach) gives a black solid. Some formulations of the catalyst hopcalite contain "Co2O3".

Dissociation (chemistry)

Dissociation in chemistry and biochemistry is a general process in which molecules (or ionic compounds such as salts, or complexes) separate or split into smaller particles such as atoms, ions, or radicals, usually in a reversible manner. For instance, when an acid dissolves in water, a covalent bond between an electronegative atom and a hydrogen atom is broken by heterolytic fission, which gives a proton (H+) and a negative ion. Dissociation is the opposite of association or recombination.


Effervescence is the escape of gas from an aqueous solution and the foaming or fizzing that results from that release. The word effervescence is derived from the Latin verb fervere (to boil), preceded by the adverb ex. It has the same linguistic root as the word fermentation.

Effervescence can also be observed when opening a bottle of champagne, beer or carbonated beverages such as soft drinks. The visible bubbles are produced by the escape from solution of the dissolved gas (which itself is not visible while dissolved in the liquid).

Although CO2 is most common for beverages, nitrogen gas is sometimes deliberately added to certain beers. The smaller bubble size creates a smoother beer head. Due to the poor solubility of nitrogen in beer, kegs or widgets are used for this.

In the laboratory, a common example of effervescence is seen if hydrochloric acid is added to a block of limestone. If a few pieces of marble or an antacid tablet are put in hydrochloric acid in a test tube fitted with a bung, effervescence of carbon dioxide can be witnessed.

This process is generally represented by the following reaction, where a pressurized dilute solution of carbonic acid in water releases gaseous carbon dioxide at decompression:

In simple terms, it is the result of the chemical reaction occurring in the liquid which produces a gaseous product.


Evaporite ( ) is the term for a water-soluble mineral sediment that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as ocean deposits, and non-marine, which are found in standing bodies of water such as lakes. Evaporites are considered sedimentary rocks and are formed by chemical sediments.

Flavin group

Flavin (from Latin flavus, "yellow") is the common name for a group of organic compounds based on pteridine, formed by the tricyclic heterocycle isoalloxazine. The biochemical source is the vitamin riboflavin. The flavin moiety is often attached with an adenosine diphosphate to form flavin adenine dinucleotide (FAD), and, in other circumstances, is found as flavin mononucleotide (or FMN), a phosphorylated form of riboflavin. It is in one or the other of these forms that flavin is present as a prosthetic group in flavoproteins.

The flavin group is capable of undergoing oxidation-reduction reactions, and can accept either one electron in a two-step process or two electrons at once. Reduction is made with the addition of hydrogen atoms to specific nitrogen atoms on the isoalloxazine ring system:

In aqueous solution, flavins are yellow-coloured when oxidized, taking a red colour in the semi-reduced anionic state or blue in the neutral (semiquinone) state, and colourless when totally reduced. The oxidized and reduced forms are in fast equilibrium with the semiquinone (radical) form, shifted against the formation of the radical:

Flox + FlredH2 ⇌ FlH•where Flox is the oxidized flavin, FlredH2 the reduced flavin (upon addition of two hydrogen atoms) and FlH• the semiquinone form (addition of one hydrogen atom).

In the form of FADH2, it is one of the cofactors that can transfer electrons to the electron transfer chain.

Hydroiodic acid

Hydroiodic acid (or hydriodic acid) is a highly acidic aqueous solution of hydrogen iodide (HI)

(concentrated solution usually 48 - 57% HI). It is the second strongest hydrohalic acid, after hydroastatic acid. Hydroiodic acid is a commonly used chemical reagent and is one of the strong acids that ionize completely in an aqueous solution.


Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, a ligand, a nucleophile, and a catalyst. The hydroxide ion forms salts, some of which dissociate in aqueous solution, liberating solvated hydroxide ions. Sodium hydroxide is a multi-million-ton per annum commodity chemical. A hydroxide attached to a strongly electropositive center may itself ionize, liberating a hydrogen cation (H+), making the parent compound an acid.

The corresponding electrically neutral compound HO• is the hydroxyl radical. The corresponding covalently-bound group –OH of atoms is the hydroxy group.

Hydroxide ion and hydroxy group are nucleophiles and can act as a catalysts in organic chemistry.

Many inorganic substances which bear the word "hydroxide" in their names are not ionic compounds of the hydroxide ion, but covalent compounds which contain hydroxy groups.

Iodine test

The iodine test is used to test for the presence of starch. Starch turns into an intense "blue-black" colour upon addition of aqueous solutions of the triiodide anion, due to the formation of an intermolecular charge-transfer complex. In the absence of starch, the brown colour of the aqueous solution remains. This interaction between starch and triiodide is also the basis for iodometry.


Metampicillin (INN) is a penicillin antibiotic. It is prepared by the reaction of ampicillin with formaldehyde, and is hydrolysed in aqueous solution with the formation of ampicillin. Hydrolysis is rapid under acid conditions, e.g., in the stomach, less rapid in neutral media, and incomplete in solutions such as human serum.


Nobelium is a synthetic chemical element with the symbol No and atomic number 102. It is named in honor of Alfred Nobel, the inventor of dynamite and benefactor of science. A radioactive metal, it is the tenth transuranic element and is the penultimate member of the actinide series. Like all elements with atomic number over 100, nobelium can only be produced in particle accelerators by bombarding lighter elements with charged particles. A total of twelve nobelium isotopes are known to exist; the most stable is 259No with a half-life of 58 minutes, but the shorter-lived 255No (half-life 3.1 minutes) is most commonly used in chemistry because it can be produced on a larger scale.

Chemistry experiments have confirmed that nobelium behaves as a heavier homolog to ytterbium in the periodic table. The chemical properties of nobelium are not completely known: they are mostly only known in aqueous solution. Before nobelium's discovery, it was predicted that it would show a stable +2 oxidation state as well as the +3 state characteristic of the other actinides: these predictions were later confirmed, as the +2 state is much more stable than the +3 state in aqueous solution and it is difficult to keep nobelium in the +3 state.

In the 1950s and 1960s, many claims of the discovery of nobelium were made from laboratories in Sweden, the Soviet Union, and the United States. Although the Swedish scientists soon retracted their claims, the priority of the discovery and therefore the naming of the element was disputed between Soviet and American scientists, and it was not until 1997 that International Union of Pure and Applied Chemistry (IUPAC) credited the Soviet team with the discovery, but retained nobelium, the Swedish proposal, as the name of the element due to its long-standing use in the literature.

Phosphoric acid

Phosphoric acid (also known as orthophosphoric acid or phosphoric(V) acid) is a weak acid with the chemical formula H3PO4. Orthophosphoric acid refers to phosphoric acid, which is the IUPAC name for this compound. The prefix ortho- is used to distinguish the acid from related phosphoric acids, called polyphosphoric acids. Orthophosphoric acid is a non-toxic acid, which, when pure, is a solid at room temperature and pressure. The conjugate base of phosphoric acid is the dihydrogen phosphate ion, H2PO−4, which in turn has a conjugate base of hydrogen phosphate, HPO2−4, which has a conjugate base of phosphate, PO3−4. Phosphates are essential for life, being building blocks for both DNA and RNA.The most common source of phosphoric acid is an 85% aqueous solution; such solutions are colourless, odourless, and non-volatile. The 85% solution is a syrupy liquid, but still pourable. Although phosphoric acid does not meet the strict definition of a strong acid, the 85% solution can still severely irritate the skin and damage the eyes.

Potassium hexafluorophosphate

Potassium hexafluorophosphate is the chemical compound with the formula KPF6. This colourless salt consists of potassium cations and hexafluorophosphate anions. It is prepared by the reaction:

PCl5 + KCl + 6 HF → KPF6 + 6 HClThis exothermic reaction is conducted in liquid hydrogen fluoride. The salt is stable in hot alkaline aqueous solution, from which it can be recrystallized. The sodium and ammonium salts are more soluble in water whereas the rubidium and caesium salts are less so.

KPF6 is a common laboratory source of the hexafluorophosphate anion, a non-coordinating anion that confers lipophilicity to its salts. These salts are often less soluble than the closely related tetrafluoroborates.

Sodium hypobromite

Sodium hypobromite is the inorganic compound with the formula NaBrO. It is usually obtained as the pentahydrate, so the material that is usually called sodium hypobromite has the formula NaOBr.5H2O. It is a yellow-orange solid that is soluble in water. It is the Na+ salt of OBr-. It is the bromine analogue of sodium hypochlorite, the active ingredient in common bleach. In practice the salt is usually encountered as an aqueous solution.

Sodium hypobromite arises by treatment of aqueous solution of bromine with base:

Br2 + 2 NaOH → NaBr + NaOBr + H2OIt can be prepared in situ for use as a reagent, such as in the synthesis of 3-aminopyridine from nicotinamide. FGI of a primary amide to an amine is obviously the Hofmann rearrangement.

Spot test (lichen)

A spot test in lichenology is a spot analysis used to help identify lichens. It is performed by placing a drop of a chemical on different parts of the lichen and noting the color change (or lack thereof) associated with application of the chemical. The tests are routinely encountered in dichotomous keys for lichen species, and they take advantage of the wide array of secondary metabolites produced by lichens and their uniqueness among taxa. As such, spot tests reveal the presence or absence of chemicals in various parts of a lichen. They were first proposed by the William Nylander (botanist) in 1866.The three most common spot tests are:

K test: a 10% aqueous solution of potassium hydroxide (KOH), or, in the absence of KOH, a 10% aqueous solution of sodium hydroxide (NaOH, lye), which provides nearly identical results;

C test: A 5.25% solution of sodium hypochlorite or undiluted household bleach; and

P test: an ethanolic solution of para-phenylenediamine, made by placing a drop of ethanol (70-95%) over a few crystals of the chemical (yielding an unstable solution).Although the above tests are most common, a KC test may be performed by wetting the thallus with K followed immediately by C. In addition, Lugol’s iodine may be useful in identifying certain species.

Strong electrolyte

A strong electrolyte is a solution/solute that completely, or almost completely, ionizes or dissociates in a solution. These ions are good conductors of electric current in the solution.

Originally, a "strong electrolyte" was defined as a chemical that, when in aqueous solution, is a good conductor of electricity. With a greater understanding of the properties of ions in solution, its definition was replaced by the present one.

A concentrated solution of this strong electrolyte has a lower vapor pressure than that of pure water at the same temperature. Strong acids, strong bases and soluble ionic salts that are not weak acids or weak bases are strong electrolytes.

A substance whose aqueous solution or molten state decomposed into ions by passing electricity is known as electrolytes.


Telenzepine is a thienobenzodiazepine acting as selective M1 antimuscarinic. It is used in the treatment of peptic ulcers. Telenzepine is atropisomeric, in other words the molecule has a stereogenic C–N-axis. In neutral aqueous solution it displays a half-life for racemization of the order of 1000 years. The enantiomers have been resolved. The activity is related to the (+)-isomer which is about 500-fold more active than the (–)-isomer at muscarinic receptors in the rat cerebral cortex.

Zinc iodide

Zinc iodide is a chemical compound of zinc and iodine, ZnI2. The anhydrous form is white and readily absorbs water from the atmosphere. It can be prepared by the direct reaction of zinc and iodine in refluxing ether. or by reacting zinc with iodine in aqueous solution:

Zn + I2→ ZnI2At 1150 °C, zinc iodide vapour dissociates into zinc and iodine.

In aqueous solution the following have been detected, octahedral Zn(H2O)62+, [ZnI(H2O)5]+ and tetrahedral ZnI2(H2O)2, ZnI3(H2O)− and ZnI42−.The structure of crystalline ZnI2 is unusual, and while zinc atoms are tetrahedrally coordinated, as in ZnCl2, groups of four of these tetrahedra share three vertices to form “super-tetrahedra” of composition {Zn4I10}, which are linked by their vertices to form a three-dimensional structure. These "super-tetrahedra" are similar to the P4O10 structure.

Molecular ZnI2 is linear as predicted by VSEPR theory with a Zn-I bond length of 238 pm.

and related quantities


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