Solubility Equilibria Will it all dissolve, and if not, how much
will? Slide 2 SOLUBILITY EQUILIBRIA Solubility: Relative term used
to describe how much of a particular substance dissolves in a
certain amount of solvent. Substances that dissolve very well are
said to be soluble Insoluble species dont dissolve well. All
substances are soluble to some extent We will look at slightly
soluble substances Slide 3 All dissolving is an equilibrium. If
there is not much solid it will all dissolve. As more solid is
added the solution will become saturated. Solid dissolved The solid
will precipitate as fast as it dissolves, forming an equilibrium.
SOLUBILITY EQUILIBRIA Slide 4 Watch out Solubility is not the same
as solubility product. Solubility product is an equilibrium
constant. It doesnt change except with temperature. Solubility is
an equilibrium position for how much can dissolve. A common ion can
change this. Slide 5 K sp Values for Some Salts at 25 C
NameFormulaK sp Barium carbonate BaCO 3 2.6 x 10 -9 Barium chromate
BaCrO 4 1.2 x 10 -10 Barium sulfate BaSO 4 1.1 x 10 -10 Calcium
carbonate CaCO 3 5.0 x 10 -9 Calcium oxalate CaC 2 O 4 2.3 x 10 -9
Calcium sulfate CaSO 4 7.1 x 10 -5 Copper(I) iodide Cu I 1.3 x 10
-12 Copper(II) iodate Cu( I O 3 ) 2 6.9 x 10 -8 Copper(II) sulfide
CuS 6.0 x 10 -37 Iron(II) hydroxide Fe(OH) 2 4.9 x 10 -17 Iron(II)
sulfide FeS 6.0 x 10 -19 Iron(III) hydroxide Fe(OH) 3 2.6 x 10 -39
Lead(II) bromide PbBr 2 6.6 x 10 -6 Lead(II) chloride PbCl 2 1.2 x
10 -5 Lead(II) iodate Pb( I O 3 ) 2 3.7 x 10 -13 Lead(II) iodide Pb
I 2 8.5 x 10 -9 Lead(II) sulfate PbSO 4 1.8 x 10 -8 NameFormulaK sp
Lead(II) bromide PbBr 2 6.6 x 10 -6 Lead(II) chloride PbCl 2 1.2 x
10 -5 Lead(II) iodate Pb( I O 3 ) 2 3.7 x 10 -13 Lead(II) iodide Pb
I 2 8.5 x 10 -9 Lead(II) sulfate PbSO 4 1.8 x 10 -8 Magnesium
carbonate MgCO 3 6.8 x 10 -6 Magnesium hydroxide Mg(OH) 2 5.6 x 10
-12 Silver bromate AgBrO 3 5.3 x 10 -5 Silver bromide AgBr 5.4 x 10
-13 Silver carbonate Ag 2 CO 3 8.5 x 10 -12 Silver chloride AgCl
1.8 x 10 -10 Silver chromate Ag 2 CrO 4 1.1 x 10 -12 Silver iodate
Ag I O 3 3.2 x 10 -8 Silver iodide Ag I 8.5 x 10 -17 Strontium
carbonate SrCO 3 5.6 x 10 -10 Strontium fluoride SrF 2 4.3 x 10 -9
Strontium sulfate SrSO 4 3.4 x 10 -7 Zinc sulfide ZnS 2.0 x 10 -25
Slide 6 SOLUBILITY PRODUCT CONSTANTS Consider the following
reaction The equilibrium constant expression is K sp = [Pb 2+ ][Cl
- ] 2 K sp is called the solubility product constant or simply
solubility product For a compound of general formula, M y X z (next
page) Slide 7 K sp = [M z+ ] y [X y- ] z K sp = [Mg 2+ ][NH 4 +
][PO 4 3- ] K sp = [Zn 2+ ][OH - ] 2 K sp = [Ca 2+ ] 3 [PO 4 3- ] 2
Slide 8 Molar solubility: the number of moles that dissolve to give
1 liter of saturated solution As with any equilibrium constant the
numerical value must be determined from experiment The K sp
expression is useful because it applies to all saturated solutions
- the origins of the ions are not relevant Consider that @ 25 C K
sp AgI = 1.5 x 10 -16 Slide 9 Solving Solubility Problems For the
salt AgI at 25 C, K sp = 1.5 x 10 -16 AgI(s) Ag + (aq) + I - (aq) I
C E O O +x x x 1.5 x 10 -16 = x 2 x = solubility of AgI in mol/L =
1.2 x 10 -8 M Slide 10 Solving Solubility Problems For the salt
PbCl 2 at 25 C, K sp = 1.6 x 10 -5 PbCl 2 (s) Pb 2+ (aq) + 2Cl -
(aq) I C E O O +x +2x x 2x 1.6 x 10 -5 = (x)(2x) 2 = 4x 3 x =
solubility of PbCl 2 in mol/L = 1.6 x 10 -2 M Slide 11 Relative
Solubilities Ksp will only allow us to compare the solubility of
solids the that fall apart into the same number of ions. The bigger
the Ksp of those the more soluble. If they fall apart into
different number of pieces you have to do the math. NameFormulaK sp
Iron(II) hydroxide Fe(OH) 2 4.9 x 10 -17 Iron(II) sulfide FeS 6.0 x
10 -14 Iron(III) hydroxide Fe(OH) 3 2.6 x 10 -39 Slide 12 The
Common Ion Effect When the salt with the anion of a weak acid is
added to that acid: it reverses the dissociation of the acid.
lowers the percent dissociation of the acid. The same principle
applies to salts with the cation of a weak base.. The calculations
are the same as with acid base equilibrium. Slide 13 Solving
Solubility with a Common Ion For the salt AgI at 25 C, K sp = 1.5 x
10 -16 What is its solubility in 0.05 M NaI? AgI(s) Ag + (aq) + I -
(aq) I C E 0.05 O +x x 0.05+x 1.5 x 10 -16 = (x)(0.05+x) (x)(0.05)
x = solubility of AgI in mol/L = 3.0 x 10 -15 M Slide 14 pH and
solubility OH - can be a common ion. More soluble in acid. For
other anions if they come from a weak acid they are more soluble in
a acidic solution than in water. CaC 2 O 4 Ca +2 + C 2 O 4 -2 H + +
C 2 O 4 -2 HC 2 O 4 - Reduces C 2 O 4 -2 in acidic solution. Slide
15 Precipitation The reaction quotient (called ion product) may be
applied to solubility equilibria - determines if a substance will
precipitate from solution Ion Product, Q =[M + ] a [Nm - ] b If
KspQ No precipitate, forward process occurs Slide 16 Precipitation
Example A solution of 75.0 mL of 0.020 M BaCl 2 is added to 125.0
mL of 0.040 M Na 2 SO 4. Will a precipitate form? (Ksp= 1.5 x 10 -9
M BaSO 4 ) BaSO 4 could form if K sp
