Solution Thermodynamics

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Solution Thermodynamics
Solubility
Solubility is the physical property describing
the ability of a given substance, the solute, to
dissolve in a solvent. Solubility is measured in
terms of the maximum amount of solute dissolved
in a solvent at equilibrium. The resulting
solution is called a saturated solution. Under
certain conditions the equilibrium solubility can
be exceeded to give a so-called supersaturated
solution, which is metastable.
lt ABgt --gt Az Bz-
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Solution Thermodynamics
Solubility, example
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Solution Thermodynamics
Solubility, example pure water
CAg2CSO4 Assume for both ions g1
Ac0.5085 B0.3281x108 cm-1 aAg2.5x10-8 cm
aSO44.25x10-8 cm
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Solution Thermodynamics
Solubility, example pure water
CAg2CSO4 use calculated g for both ions
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Solution Thermodynamics
Solubility, example pure water
CAg2CSO4 keep iterating using calculated g for
both ions until CAg becomes constant see table
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Solution Thermodynamics
Solubility, example pure water
Iteration IC gAg gSO4 CAg (moles/l)
1 0 1 1 0.0292
2 0.0438 0.812 0.473 0.0431
3 0.065 0.787 0.408 0.0463
4 0.0694 0.776 0.411 0.0468
5 0.0702 0.775 0.410 0.0468
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Solution Thermodynamics
Solubility, salt and sulfate salt addition
2 10-2 M Na2SO4 addition
1 10-2 M NaCl addition
1 main difference is in calculation of Ic
2 both Ic and solubility difference
CAg 4.83x10-2 M -- 3 increase in Ag
concentration
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Solution Thermodynamics
Solubility, salt and sulfate salt addition
2 both Ic and solubility difference
2 10-2 M Na2SO4 addition
2 initially use Cadd, then iterate with
previous (CaddS/2)
CAg 4.38x10-2 M -- 6 decrease in Ag
concentration
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Solution Thermodynamics
Solubility and Complexation
A complex ion has a metal ion at its centre with
a number of other molecules or ions surrounding
it. These can be considered to be attached to
the central ion by co-ordinate (dative covalent)
bonds. A co-ordinate bond (also called a dative
covalent bond) is a covalent bond (a shared pair
of electrons) in which both electrons come from
the same atom.
6 (the number of waters of hydration) is also
the coordination number
Al(H2O)6 3
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Solution Thermodynamics
Solubility and Complexation
Bidentate
Tetrahedral
Hexadentate
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Solution Thermodynamics
Solubility and complexation
In certain cases, some metal ion can form
complexes with a varying number of complexing
agents
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Solution Thermodynamics
Solubility and Complexation
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Solution Thermodynamics
Solubility and Complexation
Solution Silver Balance
Solution Iodide Balance
Solution Charge Balance
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Solution Thermodynamics
Solubility and Complexation
Assumes solid ltAgIgt present Assume ligand (I-
here) in excess
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Solution Thermodynamics
Solubility and Complexation
Solution Silver Balance
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Solution Thermodynamics
Solubility and Complexation
Agtot0.001 M
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Solution Thermodynamics
Solubility and Complexation
Solution species only
Altot0.01 M