Simultaneous Equilibria Ksp And Kd
8/14/2013
Complex Ion Equilibria
• The dissociation of complex ions can be represented similarly to equilibria.
Simultaneous Equilibria:
Solubility Product Constants and
Complex Ion Equilibria
→ Ag + + 2 NH
Ag(NH3 ) +2 ←
3
[Ag ][NH ]
=
[Ag(NH ) ]
2
+
Kd
3
+
3 2
→ Cu 2+ + 4 NH
Cu(NH 3 ) 24+ ←
3
[Cu ][NH ]
=
[Cu(NH ) ]
4
2+
Kd
Complex Ion Equilibria
3
2+
3 4
3
Complex Ion Equilibria
• A metal ion coordinated to several neutral molecules or anions forms compounds called complex ions.
• Familiar examples of complex ions include:
•
•
Ag(NH3 )+2 Cu(NH3 )+4
Complex ion equilibrium constants are called dissociation constants.
Example: Calculate the concentration of silver ions in a solution that is 0.010 M in
[Ag(NH3)2]+.
– Kd = 6.3 x 10-8
Co(NH3 )2 Cl2 Pt(NH3 )+2
2
4
1
8/14/2013
Complex Ion Equilibria
[Ag ][NH ] = 6.3×10
=
[Ag(NH ) ]
2
+
Kd
Complex Ion Equilibria
−8
3
+
3 2
(x)(2x)2
Kd =
(0.010 − x)
• How many moles of ammonia must be added to 2.00
L of water so that it will just dissolve 0.010 mole of silver chloride, AgCl?
= 6.3 ×10−8
– What is the stoichiometric amount of NH3 needed to form Ag(NH3)2+ ?
• STOICHIOMETRIC amount
4x3 = 6.3×10−10
– What is the equilibrium NH3 concentration needed to maintain the silver-ammonia complex?
x3 = 1.6×10−10
[ ]
x = 5.4 ×10−4 M = Ag+
• EQUILIBRIUM amount
5
7
Complex Ion Equilibria and
Precipitate Dissolution
• Copper(II) hydroxide, which is light blue colored, dissolves in aqueous ammonia to form dark blue, [Cu(NH3)4]2+.
Cu(OH)2(s ) + 4 NH3(aq )
Cu(OH)2(s )
→
←
Cu(2aq+ ) + 4NH3
→
←
Cu(NH3 ) 24+(aq ) + 2 OH−
Cu(2aq+ ) + 2 OH(−aq )
→
←
Cu(NH3 ) 24+(aq )
2
Complex Ion Equilibria
• The dissociation of complex ions can be represented similarly to equilibria.
Simultaneous Equilibria:
Solubility Product Constants and
Complex Ion Equilibria
→ Ag + + 2 NH
Ag(NH3 ) +2 ←
3
[Ag ][NH ]
=
[Ag(NH ) ]
2
+
Kd
3
+
3 2
→ Cu 2+ + 4 NH
Cu(NH 3 ) 24+ ←
3
[Cu ][NH ]
=
[Cu(NH ) ]
4
2+
Kd
Complex Ion Equilibria
3
2+
3 4
3
Complex Ion Equilibria
• A metal ion coordinated to several neutral molecules or anions forms compounds called complex ions.
• Familiar examples of complex ions include:
•
•
Ag(NH3 )+2 Cu(NH3 )+4
Complex ion equilibrium constants are called dissociation constants.
Example: Calculate the concentration of silver ions in a solution that is 0.010 M in
[Ag(NH3)2]+.
– Kd = 6.3 x 10-8
Co(NH3 )2 Cl2 Pt(NH3 )+2
2
4
1
8/14/2013
Complex Ion Equilibria
[Ag ][NH ] = 6.3×10
=
[Ag(NH ) ]
2
+
Kd
Complex Ion Equilibria
−8
3
+
3 2
(x)(2x)2
Kd =
(0.010 − x)
• How many moles of ammonia must be added to 2.00
L of water so that it will just dissolve 0.010 mole of silver chloride, AgCl?
= 6.3 ×10−8
– What is the stoichiometric amount of NH3 needed to form Ag(NH3)2+ ?
• STOICHIOMETRIC amount
4x3 = 6.3×10−10
– What is the equilibrium NH3 concentration needed to maintain the silver-ammonia complex?
x3 = 1.6×10−10
[ ]
x = 5.4 ×10−4 M = Ag+
• EQUILIBRIUM amount
5
7
Complex Ion Equilibria and
Precipitate Dissolution
• Copper(II) hydroxide, which is light blue colored, dissolves in aqueous ammonia to form dark blue, [Cu(NH3)4]2+.
Cu(OH)2(s ) + 4 NH3(aq )
Cu(OH)2(s )
→
←
Cu(2aq+ ) + 4NH3
→
←
Cu(NH3 ) 24+(aq ) + 2 OH−
Cu(2aq+ ) + 2 OH(−aq )
→
←
Cu(NH3 ) 24+(aq )
2