Solubility

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Solubility Lesson 4 Calculating Ksp
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Ksp Ksp (the solubility product
constant) is the product of the ion
concentrations in a saturated solution raised to
the power of their coefficients in the
equilibrium. Ksp is indeed a constant. Only
temperature changes can change the value of
Ksp. The higher the value of Ksp, the higher the
solubility. We can find the solubility
product constant (Ksp) for certain compounds at
25 ºC Refer to your Ksp table on page 333 of
your textbook. Provided for you.

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1. The solubility of BaCO3 is 5.1 x 10-5 M _at_
250 C. Calculate the solubility product or Ksp.
BaCO3(s) ? Ba2 CO32-
x x x
Ksp Ba2CO32-
Ksp xx
Ksp x2
Ksp (5.1 x 10-5)2
Ksp 2.6 x 10-9
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Ksp
Solubility Product
Saturated solutions- at equilibrium
No Units
Increasing Temperature (for endothermic
reactions) increases the solubility and
therefore, increases the Ksp
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Only 2 types of questions

• Calculate the solubility product, Ksp.
• Calculate the concentration of the
  ion/solubility, calculate he mass (that is, how
  many grams?) etc

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2. The solubility of PbBr2 is 0.012 M _at_ 25 0C.
Calculate the Ksp.

dissociation equation
PbBr2(s) ? Pb2 2Br-
solubility
x x 2x
equilibrium expression
Ksp Pb2Br-2
Ksp x2x2
substitute solve
Ksp 4x3
Ksp 4(0.012)3
Ksp 6.9 x 10-6
Note that the Br- is doubled and then squared!
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3. If 0.00243 g of Fe2(CO3)3 is required to
saturate 100.0 mL of solution. What is the
solubility product?
Fe2(CO3)3 ? 2Fe3 3CO32-
x 2x 3x
Ksp Fe32CO32-3
x 1 mole
0.00243 g
Molarity
291.6 g
Ksp 2x23x3
0.100 L
Ksp 108x5
Ksp 108(8.333 x 10-5)5
8.333 x 10-5 M
Ksp 4.34 x 10-19
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TRY

• If 0.0047 g of Fe(OH)3 is required to saturate
  200.0 mL of solution. What is the solubility
  product?

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What if you are asked to find ion
concentrations/solubility or mass?
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Calculate the molar solubility of iron(II)
hydroxide from its Ksp.

• Write dissociation equation
• Find corresponding Ksp expression

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TRY what mass is dissolved in 275 mL of
saturated silver bromate?
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Last few tips

• Dont ever start a question without writing the
  dissociation equation first.
• Dont forget to BALANCE this equation.
• Dont forget to use your coefficients as powers
  in Ksp equation
• Use molar mass when converting from grams?moles
  or moles? grams.

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• Homework Try ALL of these questions!
• Hebden Pg 95
• 43, 44, 46, 47, 49, 50, 52, 55