Solubility
the solubility of a material indicates whether and to which extent a pure material in one Solvent to be solved can. It designates thus the characteristic of a material to mix itself under homogeneous distribution ( as atoms , molecules or ions) with the solvent. Usually the solvent is a liquid. In addition, there is firm solutions,like e.g.And semiconductor endowed alloys , glasses , ceramic materials. With the solution of gases in liquids the term “solubility” designates a coefficient, that the mass of gas solved in the diffusion equilibrium with the gas area in the liquid related to thatPressure of the gas indicates.
One differentiates between
- the qualitative solubility (the material is soluble in a certain solvent?) and
- the quantitative solubility (which amount of material can be solved in a litre of a certain solvent?).
Table of contents |
qualitative solubility
today one knows that there must always be a certain solubility at temperatures over the absolute zero alone for thermodynamic reasons (entropy) for each material in every other material. The ever more exactly becoming analysis method confirm that. Thereforestrictly taken a distinction between soluble and unsolvably cannot be met. It concerns thus semiquantitative statements as with difficulty solubly, limited solubly or for an unlimited period solubly.
In which liquids a solid is well soluble, hangs of the molecular characteristicsthe material and the liquid off. Like that salt-like materials ( ions - connections) are nearly only in “polar” solvents such as water or also hydrogen fluoride (HF) soluble. Many lipophilic, z. B. waxlike, materials are against it only in organic solvents how Gasoline (a “apolares” solvent) considerably solubly. “Polar” means in this connection that the molecules of the solvent exhibit a dipole moment and therefore with loaded (ions) or for their part steps polar molecules of the substance in reciprocal effect, which can be loosened, however without it tooa reaction comes. The polarity of solvents is scalable. Different polarities and thus different solubilities in Chromatografie - procedures are extensively used.
Many substances, like for example ethanol (drinking alcohol) are well soluble both in water and apolaren solvents. Acetone is mixable with nearly each liquid.
quantitative solubility
the solubility of a material in a solvent is not limited in all cases. So Saccharose with water is mixable in any relationship.
During the mixture of phenolwith water there are against it two ranges: a solution of phenol in water and a solution of water in phenol. Between them a range remains “more forbidden” mixing proportion left blank, which leads to the training of a layering of two liquid phases.
The quantitative solubilitythe quantity of a material gives on with limits for soluble systems, which under given conditions (temperature, pressure, if differently not indicated standard conditions) maximally in a certain quantity of the solution soluble is. With salts the solubility follows outthe Löslichkeitsprodukt. None of the ions involved is present additionally from another source, the solubility of the betreffenbden salt can be computed:
<math> K_L = c_ {eq} \ mathrm {(A^+) ^m} c_ {eq} \ mathrm {(B^) ^n} </math>
The solubility of the salt A m B n:
<math> L= \ frac {c_ {eq} \ mathrm (A^+)}{m} = \ frac {c_ {eq} \ mathrm (B^)}{n} = \ sqrt [n+m] {\ frac {K_L} {n^n \ cdot m^m}}
< /math>
In mixed solutions, like in e.g. , it seems to natural landing on water regularly that the concentrations of anions and cations do not agree stoichiometrically in pairs, how it would correspond to the solution of individual salts.An important example for this is the solved lime, which goes through solved carbon dioxide as calcium hydrogencarbonate into solution and which to the water hardness forms substantial contribution. Over the dissociation equilibrium of carbonic acid shift with the constantly changing carbon dioxide contents of the water (e.g.by respiration and photosynthesis of the water organisms) also the concentrations that carbonate - and hydrogencarbonate - anions, while the concentration that calcium - cations by it first remains unaffected. In this case the product of the concentrations äquvalenten at all decides at calcium andCarbonate ions over it whether and to which extent it because of an excess of the Löslichkeitsproduktes to a precipitation of calcium carbonate (e.g. as boiler scale or sea-chalk) comes.
The quantitative solubility is generally indicated, like the concentration of solutions, in different units:
- g/l solution
- g/100 g solution (“weight percentage”, more correctly: “Mass per cent”)
- ml/100 ml solution (“percent by volume”, volume. - %)
- g/kg of solution
- mol/l solution (mol airty)
- Val/l solution (normality, actually becomes outdated, but in chemistryand still far) mol/
- kg of solvents (Molalität) spreads medical laboratories
example of the solubility computation of a single salt
computation of the solubility L of aluminium sulfate in water, with well-known K L
<math>
\ mathrm {2 \; Al^ {3+} + 3 \; SO^ {2} _4 \; \ overrightarrow {\ longleftarrow} Al_2 (SO_4) _3}< /math>
<math> K_L = c_ {eq} \ mathrm {(Al^ {3+}) ^2}\ c_ {eq} \ mathrm {(SO^ {2} _4) ^3 cdot}< /math>
That means: From each formula unit aluminium sulfate 2 aluminum ions and 3 sulfate ions develop in the solution.
Further the following connection between reaction constant of K L and the solubility L applies:
<math> c_ {eq} \ mathrm {(Al^ {3+}) = 2} \; L \ qquad and/or \ qquad c_ {eq} \ mathrm {(SO^ {2} _4) = 3} \; L< /math>
The factors before Lexplain themselves by the stoichiometric factor.
One uses this now into the equation for K L , from this follows then:
<math> K_L = (2 \; L) ^2 \ cdot (3 \; L) ^3 </math>
thus
< math> L = \ [5] {\ frac {K_L sqrt} {2^2 \ cdot3^3}} </math>
Now still K L begin into the pocket calculatortype: Finished
solution of gases in liquids
at the boundary surface between gases and liquids comes it to the diffusion of Gasmolekülen between the gas area and the solution area. The entrance of molecules into the solution is proportional that Partial pressure of the gas and the withdrawal proportionally the concentration of the gas in the solution (see Henry law). With the so-called. Sättigungskonzentration prevails a dynamic equilibrium between both diffusion directions. The Sättigungskonzentration is proportional to the partial pressure in the gas area. The connecting proportionality constant becomeshere as “solubility” designates:
Usually gas solubility (gas i) = Sättigungskonzentration (i)/partial pressure (i
) decreases this “solubility” from gases in liquids with rising temperature. A deviation from the proportionality between gas pressure and Gleichgewichtskonzentration makes itself only with high pressuresnoticeably.
solution of metals in metals
in the normal linguistic usage one understands by solutions usually liquid media, but there is e.g. (at ambient temperature) also firm solutions. the alloys, thus solutions of metals in metals. Itare common because of their special material properties in use. Bronze is the oldest alloy manufactured consciously by humans. Brass and the different steel are well-known examples. Also decoration gold is usually an alloy of gold with silver (Weissgold) or copper (red gold), of themGold portion is indicated in carat.
