Aqueous solution

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An aqueous solution is a solution in which the solvent is water. It is usually shown in chemical equations as a subscript (aq). The word aqueous means pertaining to, related to, similar to, or dissolved in water. As water is an excellent solvent as well as naturally abundant, it logically has become a ubiquitous solvent in chemistry.

Substances that do not dissolve well in water are called hydrophobic ('water fearing') whereas those that do are known as hydrophilic ('water-loving'). An example of a hydrophilic substance would be the sodium chloride (ordinary table salt). 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.

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 ionised in water, whereas the weak electrolytes exhibit only a small degree of ionisation in water. Nonelectrolytes are substances that dissolve in water but do not produce any ions.

When performing calculations regarding the reacting of one or more aqueous solutions, one generally 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.

[edit] Identifying Aqueous Solutions

There is no easy way to remember what is soluble in water and what is not. These are some useful guidelines or solubility rules.

1. All compounds with Na⁺, K⁺, NH₄⁺ ions are soluble in water.
2. All nitrates (NO₃^-) and acetates (CH₃COO^-) are soluble in water.
3. Most chlorides (Cl^-) and sulfates (SO₄^2-) are soluble in water. Except the following: AgCl, PbCl₂, Hg₂Cl₂, BaSO₄ and PbSO₄.
4. Most carbonates (CO₃^2-), phosphates (PO₄^3-), sulfides (S^2-), and hydroxides (OH^-) are insoluble in water. Exceptions are LiOH, NaOH, KOH and NH_{3 (aq)}.^[1]