Anaqueous solution is asolution in which thesolvent iswater. It is mostly shown inchemical equations by appending (aq) to the relevantchemical formula. For example, a solution oftable salt, also known assodium chloride (NaCl), in water would be represented asNa+(aq) + Cl−(aq). The wordaqueous (which comes fromaqua) means pertaining to, related to, similar to, ordissolved in, water.[1][2] As water is an excellent solvent and is also naturally abundant, it is a ubiquitous solvent inchemistry. Since water is frequently used as the solvent in experiments, the word solution refers to an aqueous solution, unless the solvent is specified.[3][4]
Anon-aqueous solution is a solution in which the solvent is a liquid, but is not water.[5]
Substances that arehydrophobic ('water-fearing') do not dissolve well in water, whereas those that arehydrophilic ('water-friendly') do. An example of a hydrophilic substance is sodium chloride. In an aqueous solution the hydrogen ions (H+) and hydroxide ions (OH−) are inArrhenius balance ([H+] [OH−] =Kw = 1 x 10−14 at 298 K).Acids andbases are aqueous solutions, as part of theirArrhenius definitions.[1] An example of an Arrhenius acid ishydrogen chloride (HCl) because of its dissociation of the hydrogen ion when dissolved in water.Sodium hydroxide (NaOH) is an Arrhenius base because it dissociates the hydroxide ion when it is dissolved in water.[3]
Aqueous solutions may contain, especially in the alkaline zone or subjected to radiolysis, hydrated atomic hydrogen andhydrated electrons.[citation needed]
Aqueous solutions that conductelectric current efficiently contain strongelectrolytes, while ones that conduct poorly are considered to have weak electrolytes. Those strong electrolytes are substances that are completelyionized in water, whereas the weak electrolytes exhibit only a small degree of ionization in water.[1] 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.[3]
Nonelectrolytes are substances that dissolve in water yet maintain their molecular integrity (do not dissociate into ions). Examples includesugar,urea,glycerol, andmethylsulfonylmethane (MSM).[citation needed]
Reactions in aqueous solutions are usuallymetathesis reactions. Metathesis reactions are another term fordouble-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.[1]
A common metathesis reaction in aqueous solutions is aprecipitation reaction. This reaction occurs when two aqueous strong electrolyte solutions mix and produce an insoluble solid, also known as aprecipitate. The ability of a substance to dissolve in water is determined by whether the substance can match or exceed the strongattractive forces that water molecules generate between themselves. If the substance lacks the ability to dissolve in water, the molecules form aprecipitate.[3]
When writing the equations of precipitation reactions, it is essential to determine the precipitate. To determine the precipitate, one must consult achart of solubility. Soluble compounds are aqueous, while insoluble compounds are the precipitate. There may not always be a precipitate. Completeionic equations and net ionic equations are used to show dissociated ions in metathesis reactions. When performing calculations regarding thereacting of one or more aqueous solutions, in general one must know theconcentration, ormolarity, of the aqueous solutions.[citation needed]
