Transcript Chapter 6 Chemical Reactions - Licking Heights School District

Chapter 9
Chemical Equilibrium
9.6
Equilibrium in Saturated Solutions
General, Organic, and Biological Chemistry
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Saturated Solution
A saturated solution
 contains the maximum amount of dissolved solute
 contains solid solute
 is an equilibrium system:
rate of dissolving = rate of recrystallization
solid
ions in solution
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Solubility Product Constant
The solubility product constant for a saturated
solution
 gives the ion concentrations at constant temperature
 is expressed as Ksp
 does not include the solid, which is constant
Fe(OH)2(s)
Ksp =
General, Organic, and Biological Chemistry
Fe2+(aq) + 2OH−(aq)
[Fe2+] [OH−]2
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Learning Check
Write the Ksp expression for each of the following:
A. FeS(s)
B. Ag2CO3(s)
C. Ca(IO3)2(s)
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Solution
Write the Ksp expression for each of the following:
A. FeS(s)
Ksp =
Fe2+(aq) + S2−(aq)
[Fe2+][S2−]
B. Ag2CO3(s)
2Ag+(aq) + CO32− (aq)
Ksp = [Ag+]2 [CO32−]
C. Ca(IO3)2(s)
Ca2+(aq) + 2IO3−(aq)
Ksp = [Ca2+][IO3−]2
General, Organic, and Biological Chemistry
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Guide to Calculating Ksp
General, Organic, and Biological Chemistry
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Example of Calculating Solubility
Product Constant
Calculate the Ksp of PbSO4 (solubility 1.4 x 10–4 M).
STEP 1 Write the equilibrium equation for dissociation:
PbSO4(s)
Pb2+(aq) + SO42−(aq)
STEP 2 Write the Ksp expression:
Ksp = [Pb2+][SO42−]
STEP 3 Substitue molarity values and calculate:
Ksp = (1.4 x 10–4) x (1.4 x 10–4)
= 2.0 x 10–8
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Examples of Solubility Product
Constants
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Learning Check
What is the Ksp value of PbF2 if the solubility at
25 C is 2.6 x 10–3 M?
1) 1.4 x 10–5
2) 6.8 x 10–6
3) 7.0 x 10–8
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Solution
3) 7.0 x 10-8
STEP 1 Write the equilibrium equation for dissociation:
PbF2(s)
Pb2+(aq) + 2F−(aq)
STEP 2 Write the Ksp expression:
Ksp = [Pb2+][F−]2
STEP 3 Substitute molarity values and calculate:
[Pb2+] = 2.6 x 10–3 M
[F−] = 2 x [Pb2+] = 5.2 x 10–3 M
Ksp = (2.6 x 10–3) x (5.2 x 10–3)2 = 7.0 x 10–8
General, Organic, and Biological Chemistry
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Molar Solubility (S)
The molar solubility (S) is
 the number of moles of solute that dissolve in 1 L
of solution
 determined from the formula of the salt
 calculated from the Ksp
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Calculating Molar Solubility (S)
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Solubility Calculation
Determine the solubility (S)2 of SrCO3 (Ksp = 5.4 x 10–10).
STEP 1 Write the equilibrium equation for dissociation:
SrCO3(s)
Sr2+(aq) + CO32−(aq)
STEP 2 Write the Ksp expression:
Ksp = [Sr2+][CO32−]
STEP 3 Substitute S for the molarity of each ion into Ksp:
Ksp = [Sr2+][CO32−] = [S][S]
= S2 = 5.4 x 10−10
STEP 4 Calculate the solubility, S:
S=
= 2.3 x 10−5 M
-10
5.4  10
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Learning Check
Calculate the solubility (S) of PbSO4 , if the
Ksp = 1.6 x 10–8.
1) 1.3 x 10–4 M
2) 4.0 x 10–4 M
3) 2.6 x 10–16 M
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Solution
1) 1.3 x 10–4 M
STEP 1 Write the equilibrium equation for dissociation:
PbSO4(s)
Pb2+(aq) + SO42−(aq)
STEP 2 Write the Ksp expression:
Ksp = [Pb2+][SO42−]
STEP 3 Substitute S for the molarity of each ion into Ksp:
Ksp = [Pb2+][SO42−] = [S][S]
= S2 = 1.6 x 10–8
STEP 4 Calculate the solubility, S:
S = 1.6  10-8 = 1.3 x 10–4 M
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