Solubility

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Solubility is the amount of a solute that will dissolve in a specific solvent under given conditions. The dissolved substance is called the solute and the dissolving fluid (usually present in excess) is called the solvent, which together form a solution. The process of dissolving is called solvation, or hydration if the solvent is water.

A solution at equilibrium that cannot hold any more solute is said to be saturated. The equilibrium of a solution is mainly dependent on temperature. The maximum equilibrium amount of solute which can normally dissolve per amount of solvent is the solubility of that solute in that solvent. It is often expressed as a maximum concentration of a saturated solution. These maximum concentrations are often expressed as grams of solute per 100 milliters of solvent. The solubility of one substance dissolving in another is determined by the intermolecular forces between the solvent and solute, temperature, the entropy change that accompanies the solvation, the presence and amount of other substances, and sometimes pressure or partial pressure of a solute gas.

Solubility constants are used to describe saturated solutions of ionic compounds of relatively low solubility (see solubility equilibrium). For salts, solubility in aqueous solutions or the maximum amount of salt that can be dissolved is the solubility constant. The solubility constant is a special case of an equilibrium constant. It describes the balance between dissolved salt and undissolved salt. The solubility constant is also "applicable" (i.e. useful) to precipitation, the reverse of the dissolving reaction. As with other equilibrium constants, temperature can affect the numerical value of solubility constant.

While solutions are typically thought of as solids being mixed into liquids, any two states of matter can be mixed and be called a solution. Carbonated water is a solution of a gas in a liquid, hydrogen (a gas) can dissolve in palladium (a solid), and stainless steel is a solution of a solid in a solid (called an alloy). Phthalates dissolve in plastics and act as plasticizer.

Solutions may, under special conditions, hold more solute than the solvent can normally dissolve. This is called supersaturation.

Solvents are normally characterized as polar or nonpolar. The general rule of thumb is "Like Dissolves Like." This means that polar solvents will dissolve ionic compounds and covalent compounds which ionize, while nonpolar solvents will dissolve nonpolar covalent compounds. For example, ordinary table salt, an ionic compound, will dissolve in water, but not in ethanol.

Water and nonpolar solvents are immiscible; they do not form homogeneous mixtures but separate into two distinct phases or form milky emulsions.


Contents

[edit] Solubility of bonding type in water

This table gives some indication how the chemical bonding type relates to solubility in water.

Bonding typeSolubility in waterExample
ionicmost solubleSee below
metallicinsolubleFe
unless they react with waterK
polar covalentsoluble if it has H bondsglucose
soluble by reactionHCl
insoluble otherwiseether
non-polar covalentmost insolublebenzene
some slightly solubleO2
covalent latticeinsolublediamond

[edit] Solubility of ionic compounds in water

This table presents an overview of solubility of salts in water.

SolubleInsoluble
Group I and NH4+ compoundscarbonates (except Group I, NH4+ and uranyl compounds)
nitratessulfites (except Group I and NH4+ compounds)
acetates (ethanoates)phosphates (except Group I and NH4+ compounds)
chlorides, bromides and iodides (except Ag+, Pb2+, Cu+ and Hg22+)hydroxides and oxides (except Group I, NH4+, Ba2+, Sr2+, Ca2+ and Tl+)
sulfates (except Ag+, Pb2+, Ba2+, Sr2+ and Ca2+)sulfides (except Group I, Group II and NH4+ compounds)

For a more comprehensive chart on solubility data, visit solubility chart.

[edit] Solubility Definitions

Stated in terms of the parts of solvent needed to dissolve one part of the solute (US):

Definition Parts of solvent needed to dissolve 1 part of solute
Very soluble < 1
Freely soluble 1 - 10
Soluble 10 - 30
Sparingly soluble 30 - 100
Slightly soluble 100 - 1000
Very slightly soluble 1000 - 10,000
Insoluble > 10,000

[edit] See also

Look up solubility in
Wiktionary, the free dictionary.
Look up soluble in
Wiktionary, the free dictionary.

[edit] External links

el:Διαλυτότητα es:Solubilidad fr:Soluble hr:Topljivost hu:Oldhatóság no:Løselighet pl:Rozpuszczalność pt:solubilidade

Solubility

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