Transcript CHAPTER 17 - SOLUBILITY AND PRECIPITATION

CHAPTER 17 - SOLUBILITY
AND PRECIPITATION
Read intro on page 560
Dissolution
CaCl2(s) ↔
Ca+2(aq) + 2 Cl-(aq)
Precipitation
Ca+2(aq) + 2 Cl-(aq) ↔ CaCl2(s)
Ksp = [Ca+2] [Cl-]2
Students complete practice
problems 1 & 2 on page 565
We can look up the solubility
product constant of many
materials at 25 oC.
(see page 566).
Demonstrate problem #2 on
page 567
Students complete problems 3
& 4 on page 567.
USING KSP TO CALCULATE
ION CONCENTRATIONS
Review writing ionic equations
(worksheet).
Students earmark polyatomic ion
page in notes (or ask on a test).
Complete sample problem 3.
Students complete practice
problems 5 & 6
PREDICTING THE FORMATION
OF A PRECIPITATE
Insert the ion concentrations into
the Ksp equation and calculate the
“Ksp”.
Since we do not know if the
solution is at equilibrium, we call
the “Ksp” the ion product quotient
(Q) (same as the reaction product
quotient).
If Q = Ksp the solution is at
equilibrium.
If Q > Ksp the solution is
supersaturated and a precipitate
will form.
If Q < Ksp the solution is
unsaturated.
Chemical reactions that result in
a precipitate form a product that
has a Q greater than the
precipitate’s Ksp.
Can also predict a precipitate
rather than calculate
The rules on page 574 can be
used to predict a precipitate.
A double replacement reaction
will take place if an insoluble
(or slightly soluble) compound
is formed.
AgNO3(aq)+KBr(aq) →AgBr(s)+KNO3(aq)
A double replacement reaction
will also take place if water or a
gas is formed.
Demonstrate sample problem #4
Assign practice problems 7 & 8.
Net ionic equation
A net ionic equation includes only the
change.
Total equation
AgNO3(aq) + KBr(aq) → AgBr(s)+ KNO3(aq)
Net Ionic Equation
Ag+(aq) + Br-(aq) → AgBr(s)
NO3- and K+ are called “spectator ions”
because they do not participate in the
reaction
The common-ion effect
This is a shift in the equilibrium
because the concentration of one
of the equilibrium ions is changed.
(Le Chatelier’s Principle)
CaSO4(s)↔ Ca+2(aq) + SO4-2(aq)
What will happen if Na2SO4 is
added?
Will shift to the left
More CaSO4 will precipitate out.