Transcript Chapter 16 Aqueous Equilibria: Applications

Chapter 16 Aqueous Equilibria: Applications
1. neutralization reactions
2. common ion effect; buffers
3. titrations
strong acid - strong base
strong - weak
weak - weak
polyprotic acid - strong base
4. solubility equilibria
review precipitation reactions and solubility rules
Ksp & solubility
common ion effect
solubility & pH
5. complex ion formation
Kf
solubility
6. selective precipitation; qualitative analysis: skip
Chapter 16 Notes
1
5. complex ion formation
•what is a “complex ion”: an ionic Lewis acid-base
species that forms between a cation (Lewis acid) and
an anion or compound with a lone pair (Lewis base)
examples:
Ag1+(aq)+2NH3(aq)
Zn2+(aq)+4OH1-(aq)
Ag(NH3)21+
Zn(OH)42-
•complex ions are very stable: the equilibrium constant
for the formation of a complex ion is very large
1
K f (Ag(NH 3 ) 2 ) 
K f (Zn(OH) 4 ) 
2-
1
7

1
.
7

10
2
 NH3 
Ag 
1
1
Zn  OH 
2
1- 4
Chapter 16 Notes
 2.8 1015
2
5. complex ion formation
example:
1. Calculate the solubility of AgBr(s) in water; Ksp(AgBr)=5.4x10-13.
2. Na2(S2O3) is added to a saturated solution of AgBr. Ag+ forms a
complex ion with S2O3-2; the complex ion, Ag(S2O3)2-3 has
Kf=2.9x1013. Let's see what happens.
a. What are the predominant species in solution? What secondary
species can form?
b. What reactions, if any, can occur between any two primary
species? What reactions, if any, can occur between a primary and a
secondary species?
Chapter 16 Notes
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5. complex ion formation
example cont’d
c. Write the balanced chemical equation that shows the formation of
the secondary species. Write the balanced chemical equation that
shows the reaction between the primary and secondary species. Add
the two equations together to get the net, overall reaction which
occurs when Na2(S2O3) is added to a saturated solution of AgBr..
d. What is the equilibrium constant for the net reaction? Does S2O3-2
increase or decrease the solubility of AgBr? Why?
Chapter 16 Notes
4
5. complex ion formation
example cont’d.
e. Now calculate the solubility of AgBr in S2O3-2.
Chapter 16 Notes
5
5. complex ion formation
another example: Using Table C.6 (Appendix C) in your textbook, and
using the solubility rules, state what you would observe if the
following solutions are mixed. Write balanced chemical equations to
support your answers.
a. A solution of CuCl2 is made slightly basic with the addition of a
small amount of NH3.
b. A lot of NH3 is added to the solution from part a.
c. NaCN is added to a saturated solution of FeS.
d. A solution of Cr(NO3)3 is made slightly basic with the addition of a
small amount of NaOH.
e. A lot of NaOH is added
Chapter 16 Notes
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