Additional Aspects of Solution Equilibria

1
Additional Aspects of Solution Equilibria
2
Solubility Product Constant, Ksp

• Allows a quantitative description of solubility
• AgBr(s) ltgt Ag(aq) Br -(aq)
• Saturated soln when AgBr (s) has dissolved to
  the greatest extent possible
• Exp _at_25C Ag and Br -
• 5.7 x 10 -7 M

3
Solubility Product Constant, Ksp-cont

• AgBr(s) ltgt Ag(aq) Br -(aq)
• Ksp AgBr -
• (5.7 x 10 -7) (5.7 x 10 -7)
• 3.3 x 10 -13

4
Solubility Product Constant, Ksp-cont

• Ksp ltlt 1 insoluble
• Ksp 10-2 to 10-5 slightly soluble
• Ksp gt 10-2 soluble

5
Determining Ksp fr Exp Measures

• The solubility of AgI is 1.22 x 10-8 mol/L _at_
  25C.
• Calculate Ksp
• AgI ltgt Ag (aq) I-(aq)
• Ksp Ag I-
• (1.22 x 10-8)(1.22 x 10-8)
• 1.49 x 10-16

6
Estimating Salt Solubility fr Ksp

• Use published Ksp values (p.1127)
• The Ksp for CaCO3 3.8 x 10-9 _at_25C calculate
  solubility in moles/L and in grams /L
• CaCO3(s) ltgt Ca 2 (aq) CO 32-(aq)
• Ksp Ca2CO32-
• CaCO3(s) ltgt Ca 2 (aq) CO 32-(aq)
• I 0 0
• C x x
• E X X
• Ksp 3.8 x 10-9 X2
• X 6.2 x 10 -5 M

7
Precipitation of Insoluble Salts

• Ksp and the Reaction Quotient, Q
• Q Ksp , the sy is at equilibrium
• Q lt Ksp, not at equilibrium, soln is not
  saturated
• Q gt Ksp, not at equilibrium, soln is
  supersaturated
• Soln will ppt until Q Ksp

8
Precipitation of Insoluble Salts-cont

• Some solid AgCl has been placed in a beaker of
  water. After some time, experiment shows th the
  concs of Ag and Cl- are ea 1.2 x 10-5 mol/L.
  Has the sy reached equilibrium? If not, will
  more AgCl dissolve?
• Soln compare Q and Ksp
• Q Ag Cl- (1.2 x 10-5 )(1.2 x 10-5 )
• 1.4 x 10 -10
• Ksp 1.8 x 10 -10
• Q is less AgCl will continue to dissolve until
  Q Ksp

9
Precipitation of Insoluble Salts-cont

• Solid PbI2 (Ksp 8.7 x 10-9) is placed in a
  beaker of water. After some time, the lead(II)
  conc is found to be 1.1 x 10-3M.
• Has the system reached equilibrium?
• Is the soln saturated? If not, will more PbI2
  dissolve?

10
Ion Conc Required to Just Begin Ppt

• The conc of Ba2 , in a soln is 0.010M
• What conc of SO42- is required to just begin
  precipitating BaSO4?
• When the conc of sulfate ion in the soln reaches
  0.015 M, what is the conc of barium ions th
  remains in soln?
• BaSO4 (s) ltgt Ba2 SO42-
• Ksp Ba2 SO42- 1.1 x 10-10
• SO42- Ksp 1.1 x 10-10 1.1 x 10-8M
• Ba2 .010

11
Ion Conc Required to Just Begin Ppt

• What is the min. conc of I- th can cause ppt of
  PbI2 (Ksp 8.7 x 10 -9) fr a 0.050 M soln of
  Pb(NO3) 2 ?
• What conc of lead ions remains in soln when the
  conc of I- is .OO15M?

12
Solubility the Common Ion Effect

• The solubility product of a salt contains the
  conc of both anions cations.
• By LeChatliers Princ, adding more of either the
  anion or cation will shift the equilibrium to
  reduce the new conc
• Adding anion will reduce cation vice versa
• Q will be gt Ksp, so the reaction will proceed to
  the left to restore equil

13
Solubility the Common Ion Effect

• CaCO3(s) ltgt Ca2(aq) CO32-(aq)
• Adding Na2CO3 to this equilibrium will shift the
  equilibrium to the left, thus reduce the amount
  of Ca2 present when the new equilibrium is
  reached
• An ionic salt is always less soluble in a
  solution containing a common ion than it is in
  water.

14
Solubility pH

• Acid H donor
• Base H acceptor
• Adding an acid or a base to a sy at equilibrium
  will shift the equil to absorb the added species
• K2CrO4 HCl ltgt
• K2Cr2O7 H2O

15
Solubility, Ion Separations, Qualitative
Analysis

• Applying principles of chemical equilibria,
  allows for the separation ID of cations
  anions in aqueous solns
• By combining cations w/ anions th form insoluble
  salts, separation can be achieved

16
Coordination Compounds

• A metal ion is associated w/ a group of neutral
  molecules or anions
• May be neutral OR
• Have an overall or - charge

17
Coordination Comps- cont

• Coordination complex/ complex ion
• Fe(H2O)6Cl2
• w/in brackets is a cation,
• Fe(H2O) 6 2
• 2 Cl- are present to counter balance the charge

18
Coordination Comps- cont

• Ligands - molecules or ions attached to the metal
• Have at least 1 atom w/ a lone (unshared) e- pair
• This lone pair is shared w/ the metal (Lewis
  base)
• Coordinate covalent bond
• Ni 2 NH3 -gt Ni lt-NH3 2

19
Coordination Comps- cont

• Coordination number - the number of ligand
  molecules attached to a metal
• Have a definite structure geometry
• Ni(NH3)62 octahedral (most common)
• 4 ligands tetrahedral or square planar
• 2 ligands linear
• Follows the VSEPR theory!

20
Coordination Comps- cont

• Color changes often provide evidence for the
  interaction of ligands metal cations, esp
  transition metals.
• NiSO4(s) 6H2O(l) -gt Ni(H2O)6 2(aq)
  SO42-(aq) (green color)
• Replacing water ligands w/ ammonia-gt blue color

21
Coordination Comps- cont

• Naming Complex Ions
• Show the number identity of ea ligand attached
  to the central metal atom
• The identity oxidation number of the central
  metal atom
• Whether the complex is a cation or an anion

22
Naming Complex Ions

• 1. For anionic ligands, substitute the suffix o
  for the normal ending
• Cl- chloro SO4 2- sulfato
• OH- hydroxo CO3 2- carbonato
• Usu., molecular names are unchanged,
  exceptions
• H2O aqua NH3 amine
• The number of ligands of a particular type is
  indicated by Greek prefixes di, tri, tetra,
  penta, hexa
• Cu(H2O)42 tetraaquacopper (II)
• Cr(NH3)63 hexaaminechromium (III)

23
Naming Complex Ions

• If more than one type of ligand is present,
  follow alphabetical order.
• Cu(NH3)2(H2O)2 2
• diamminediaquacopper (II)
• 4. Oxidation number of the central atom is
  indicated by a Roman numeral written at the end
  of the name in parenthesis.

24
Naming Complex Ions

• If the complex is an anion, the suffix -ate is
  inserted between the name of the metal the oxi
  .
• Zn(OH)4 2- tetrahydroxozincate (II)
• Coordination comps are named w/ the cation 1st,
  followed by the anion.
• Cr(NH3)4Cl2NO3
• tetraaminedichlorochromium (III) nitrate