Solubility Equilibrium (Ksp)
•
Ksp Concept Overview
Solubility Chart
Negative Ions
Positive Ions
Solubility
Essentially All
Alkali ions (U\ Na% K\ Rb", Cs")
Soluble, (aq)
Essentially All
Hydrogen ion, H*
Soluble, (aq)
Essentially All
Ammonium ion, NH4*
Soluble, (aq)
Essentially All
Soluble, (aq)
Essentially All, EXCEPT Ag"
Soluble, (aq)
Nitrate, NO3
Acetate,
CH3COO
Chloride, Cl
Bromide, Br
Iodide, 1
Sulfate, so/
Sulfide, S^
Ag% Pb'^ Hg2'% Cu\ TV
All others
Ca^% Sr^% Ba^^ Pb2% Ra^"
All others
Alkali ions and H\ HH/, Be^\ Mg^', Ca^",
Sr^% Ba2% Ra^*
All others
Alkali ions and H\ HH/, Sr^", Ba'% Ra'% Tl'
Hydroxide, OH
Phosphate,
P04^
Carbonate,
COB^
All others
Alkali ions and H\ NH4'
All others
Low Solubility,
(s)
Soluble, (aq)
Low Solubility,
(s)
Soluble, (aq)
Soluble, (aq)
Low Solubility,
(s)
Soluble, (aq)
Low Solubility,
(s)
Soluble, (aq)
Low Solubility,
(s)
Sulfite, SOB^
Chromate,
Cr04^
Ba^% Sr2^ Pb^% Ag'
All others
Low Solubility,
(s)
Soluble, (aq)
C8 Solubility Product Constants (AC J
sp-
Solubility Product Constants at 25°C
Name
Formula
'fsp
barium carbonate
BaC03f3)
2.6 X 10^^
barium chromate
BaCr04(s)
1.2 X 10^1°
barium sulfate
BaSO^cs)
1.1 X 10^1°
calcium carbonate
CaC03f33
5.0 X 1 0 " ^
calcium oxalate
CaC204fs); CaOOCCOOfs)
2.3 X 1 0 " ^
calcium phosphate
Ca3(P0^2is)
2.1 X 10~33
calcium sulfate
CaS04(33
7.1 X 10-5
copperO] chloride
CuCI(33
1.7 X 1 0 " ^
copperO] iodide
Culfs)
1.3 X 10^12
copperOO iodate
cuao332Cs)
6.9 X 1 0 " ^
copperOO sulfide
CuS(33
6.0 X 10-3^
ironOO hydroxide
FeC0H)2Cs)
4.9 X 10^^^
ironOO sulfide
FeS(33
6.0 X 10"^^
ironCIII) hydroxide
FeCOH33C33
2.6 X 10^33
leadOO bromide
PbBr2(33
6.6 X 10"^
leadOD chloride
PbCl2(s)
1.2 X 10^5
3.7 X 10-^^3
leadOD iodate
Pba0332(s)
leadOD iodide
Pbl2Cs)
8.5 X 10-9
lead00 sulfate
PbSOz,cs)
1.8 X 10-«
magnesium carbonate
MgC03f33
6.8 X 10"^^
magnesium fluoride
MgFacs)
6.4 X 10-9
magnesium hydroxide
MgC0H)2Cs)
5.6 X 10-12
mercuryO) chloride
Hg2Ci2(s)
1.5 X 10-1^
silver bromate
AgBr03f33
5.3 X 10-5
silver bromide
AgBr(33
5.4 X 10-13
silver carbonate
Ag2C03Cs3
8.5 X 10-12
silver chloride
AgCI(3)
1.8 X 10-1°
silver chromate
Ag2Cr04(3)
1.1 X 10-12
silver iodate
Agi03cs3
3.2 X 10-^
silver iodide
Agi(s3
8.5 X 10-1^
strontium carbonate
SrC03C33
5.6 X 10-10
4.3 X 10-9
strontium fluoride
SrF2(3)
strontium sulfate
SrS04C33
3.4 X 10"^
zinc hydroxide
ZnCOH32(33
7.7 X 10-1^
zinc sulfide
ZnSt33
2.0 X 10-25
Values in this table are taken from The CRC Handbool< of Chemistry and
Physics, 76th Edition.
802
Appendix C
Writing Balanced Ionic Equations for Precipitate Reactions
Use the solubility chart and write the balanced dissolving ionic (DIE), overall ionic
(OIE), and the net ionic equations (NIE) when:
1. a solution of silver nitrate is mixed with sodium iodide solution.
2. solutions of potassium chromate and strontium bromide combine.
3. an ammonium hydroxide solution is mixed with a solution of copper (I) chromate.
4. aqueous lithium sulphate combines with dissolved calcium iodide.
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Phase Equilibrium in a Saturated Solution
Intro to Ksp
Calculate the solubility in grams per litre of gypsum, formula
CaS04, given a Ksp of 7.1 x 1 0"^ at 25°C.
Calculating Solubility
Calculate the solubility of strontium fluoride in mg in 2 0 0 . mL of
solution. Check C8 for Ksp at 25°C.
Calculating Solubility 2
Calculate the solubility product constant, Ksp, for silver sulfate if
1 5 mg dissolves to make a saturated solution in 1 0 0 . mL at 2 5 °
C.
Calculating Ksp
Steps to calculate Ksp from solubility.
© S I . W r i t e balanced equilibrium equation.
© S2. W r i t e Ksp expression
© S3. Calculate moles of solid.
© S4. Determine moles of ions.
© S 5 . Substitute all values into Ksp expression.
Calculate Ksp of magnesium fluoride at 2 5 ° C given that
0 . 0 0 1 7 2 g dissolves in 1 0 0 . mL of solution.
Summary of How to Calculate Ksp
Ksp Of Pbcl2
Object! ve(s):
Determine the Ksp of PbC12.
Chemical(s):
100 mL saturated PbC12 solution.
Distilled water
20 mL 0.50 M K2Cr04 solution
Safety Precautions:
Wear eye protection over eyes when working with chemicals.
Observe proper glass handling procedures.
Rinse affected areas immediately with copious quantities of water.
Clean up spills immediately.
Wash hands when iinished.
All solutions are poisonous. Observe appropriate precautions when handling.
Experimental Setup:
Quantitative Observations:
Mass of clean, dry, empty beaker:
Mass of filter paper:
.
Mass of beaker, filter paper, and dry precipitate:
Temperature of saturated PbC12 solution:
.
.
°C
Chemical Equations:
Write the balanced equilibrium dissolving equations for PbC12 and the precipitate,
including appropriate subscripts.
Calculations:
1. Calculate the moles of precipitate.
2. Calculate the Ksp of PbC12.
Conclusion:
Answer the objective.
Compare your result to the actual Ksp and comment on your experimental method.
Ksp of PbCb Lab Equipment
1. plastic funnel
2. massed & f o l d e d filter p a p e r
3. 1 0 0 mL g r a d u a t e d cylinder
4 . 150 mL beaker
5. 5 0 mL g r a d u a t e d cylinder
6. 5 0 mL beaker
7. glass stir rod
8. massed 2 5 0 mL beaker
9. burner
1 0. stand
1 1. Iron ring
1 2. wire gauze
1 3. wash bottle with distilled H2O
14. beaker tongs
1 5. 2 5 0 mL filtrate beaker
Ksp of PbCb Prelab
If 1.00 g of solid l e a d (II) chromate precipitates, calculate the
Ksp of PbCb.
Common ion Effect
The common ion effect is an example of Le Chatelier's
principle that applies to solubility equilibrium
By adding a common ion to a sparingly soluble substance, the
solubility of that substance actually changes.
Since you can't simply a d d an ion, an entire solution containing the
common ion must be a d d e d to the sparingly soluble solution.
Intro to Common Ion Effect
Common Ion Questions
Calculate the molar solubility of iron (II) hydroxide in pure
water at 25°C. Ksp is 4.9 x l 0'^^.
Convert the solubility to mg in 4 5 0 . mL of solution.
Calculate the mass of iron (III) hydroxide that dissoves in mg in
4 5 0 . mL of solution with 0.10 M sodium hydroxide solution.
By what proportion did the solubility change?
^
Common Ion Sample Question 1
Common Ion Questions
The solubility of a saturated solution changes if you add an amount
of a second solution containing a commmon ion, NOT the Ksp.
Calculate the solubility in mg in 2 0 0 mL of saturated iron (II) sulfide
solution in pure water:
a) in pure water.
b) in a solution containing 0.1 0 M sodium sulfide.
^
p.492 Q.9 b)
Common Ion Sample Problem 2
W o w ! The solubility of a sparingly soluble ionic salt decreases
when you a d d a solution containing a common ion. In this case,
it has decreased by a factor of 1 O V 0'^^ = ] 0 0 0 0 0 0 0 0 !
This is simply a quantitative application of Le Chatelier's
Principle.
Common Ion Effect Conclusion
Predicting Precipitation
p. 4 8 9 Q.5 a)
W i l l a precipitate form from the mixing of 25.0 mL of
0.010 mol/L of silver nitrate and 25.0 mL of 0.0050 mol/L
potassium chloride? Get Ksp values from p.802
^
Predicting Precipitation Sample Problem 1
C "^-D
f\^ C '^
Predicting Precipitation
Will a precipitate form if 20 mL of 0.0001 M lead (II) nitrate
solution is combined with 15 mL of 0.001 M calcium hydroxide
solution?
1/
_ ,
- - ' o " ^
Step 1. Write balanced equilibrium dissociation equation for the
precipitate using solubility rules.
> = >
Predicting Precipitation Sample Problem 2
How to Solve Predicting Precipitation Questions
Step 1. W r i t e the two balanced dissociation equations (DIE)
Step 2. Predict the precipitate that forms and write the
balanced solubility equilibrium equation, and Ksp
expression.
Step 3. Calculate the moles of each ion in the equilibrium
equation and divide them by the total volume of solution
to obtain concentrations.
Step 4 . Plug concentrations into Ksp expression to get Q.
Step 5. Compare Q value to Ksp value and determine which
direction is favoured and whether a precipitate forms.
p.489 Q.5 a) & 5b)
Summary of Predicting Precipitation
Chemistry 40S/PgL Problem Set: Solubflftv Equilibrium
1. Calculate the Ksp of iron ( I I I ) hydroxide if 1.60 x 10'^ mg dissolves in 150
mL of solution. (2)
2. A. Calculate the solubility in mg of calcium phosphate in 200 mL of pure
water. (2)
B. Calculate the solubility in mg of calcium phosphate upon the addition of
0.20 M of sodium phosphate to 200 mL of solution. (2)
C. What happens to the solubility of an ionic compound with the addition
of a common ion? (1)
Will a precipitate form if 15 mL of 0.15 M Pb(N03)2 is mixed with 100 mL
of 0.1 M Nal? Show all of your work for full marks. (2)
Selective Precipitation
Solutions containing different ions may be separated by carefully
separating the least soluble ion.
Sample Question
How much iodide solution must be added to a solution containing
0.01 mol/L Ag+ and 0.01 mol/L Pb2+ ions to selectively
precipitate the least soluble ion?
How much I" must be a d d e d before Pb^+ ions precipitate?
W h a t concentration of Ag+ remains even after the most soluble ions
begin to precipitate?
Reference: Toon et. a I. (1990). Foundations of Chemistry. Holt,
RInehart, and Winston of Canada, Limited. Toronto, p. 4 8 7
Follow Up Selective Precipitation Problem
A solution contains 0.010 mol/L Ag+ ions and 0.010 mol/L Sr^ +
ions.
a)
which ion precipitates first when dilute K2Cr04 is slowly
added to the mixture? Ksp Ag2Cr04 and SrCr04 is 1.1 x 10"^^
and 3.6 x 1 0"^, respectively.
b)
what percentage of the ion that is precipitated first
remains unprecipitated when the second ion begins to
precipitate?
Selective Precipitation Questions
1.
A solution contains 0.01 mol/L TINO3 and 0.01 mol/L
AgNOs.
a) Calculate the concentration of iodide ions required to
selectively precipitate each ion when Nal is slowly
added to the solution. Ksp values of silver iodide anc
thallium iodide are 8.3 x 10" and 8.9 x 10" ,
respectively.
3) How many mg of silver remain unprecipitated when
the second compound begins to precipitate?
Dissolving Precipitates that are Slightly Soluble
4 Things may be done, depending on the nature of the reactants.
1.
Just a d d lots of water, only if the Ksp of precipitate is around
10-3
2.
A d d a strong acid.
3.
M a k e a complex ion by adding an excess of NH3, O H , HCI
4.
M a k e a new, less soluble precipitate.
Combining Equilibrium Constants
A silver thiosulfate complex, formula Ag(S203)2^" (Kf = 2.9 x
10^^), is formed in an attempt to dissolve silver bromate,
AgBr03 (Ksp = 5.5 x 1 0"^) present in a saturated solution in
equilibrium with its ions.
a.
Write the balanced solubility equilibrium equation, complex
ion formation equation, and the overall equation
b.
Prove that Kc for the overall reaction is equal to Ksp x Kf.
Combining Equilibrium Constants
Chemistry 40S PGL Solubility Equilibrium PGL Concepts Worksheet
Selective Precipitation
1. *Given a solution containing 0.050 mol/L Mg^* and 0.020 mol/L Cu^\
a. which ion will precipitate first as OH" is added to the solution? Explain
your reasoning.
b. What is the concentration of OH necessary to begin precipitation of each
cation? (Ksp IVlgCOH)^ is 1.8 x w''\ and Ksp Cu(0H)2 is 2.2 x 10"'°)
2. *What concentration of CI- is necessary to begin precipitation from a solution
containing 1.0 x 10"' M Ag" and 2.0 x 10"' hA Pb'"? (Ksp AgCI = 1.8 x 10"'°; Ksp
PbCl2 = 1 . 7 x 1 0 " ^ ) .
^Adapted from Brown, LeMay, Burnsten (2006). Chemistry The Central Science AP Edition. Pearson
Education Canada, Inc. Toronto, Ontario, p. 755.
Dissolving Slightly Soluble Precipitates
3. Answer the following questions given the list below of slightly soluble salts
and a saturated solution of silver bromide, Ksp 5 4 x 10"^^
a. Circle the precipitate that may be formed in order
to dissolve a saturated solution of silver bromide.
Explain your reasoning.
Formula
Ksp
Ag2C03
AgBrOj
8.5x10"''
5.3 x i o " ^
8.5 X 10"'^
6.6x10"^
Agl
PbBr2
Chemistry 40S PGL Solubility Equilibrium PGL Concepts Worksheet
b. Assuming a solution containing the appropriate ion to begin precipitation
is added to saturated solution of silver bromide, write the balanced
solubility equilibrium equation, precipitate formation equation, and overall
equation.
c. Calculate Kc for the reaction from both Ksp values.
A chemistry student attempts to dissolve a saturated solution of strontium
sulfate, Ksp 3.4 x 10"'', by adding a solution containing barium ions. The Ksp for
the insoluble barium-containing precipitate is 1.1 x 10"'°.
a. Write the balanced solubility equilibrium equation, precipitate formation
equation when barium reacts, and the overall equation.
Complex Ion Formation
5. *A precipitate of copper (II) iodate (Ksp = 6.9 x 10"^) in equilibrium with its ions
may be dissolved by forming the Cu(CN)4'" complex (Kf = 1 x 10'^) when excess
CN" ions are added to a saturated solution of Cu(l03)2. Note that the copper
(II) ion is involved in the formation of the complex ion.
a. Write the balanced solubility equilibrium equation, complex ion formation
equation, and the overall equation.
b. Calculate Kc for the reaction from both K values.
Chemistry 40S PGL Solubility Equilibrium PGL Concepts Worksheet
6. ^Starting with a saturated solution of iron (II) hydroxide (Ksp = 4-9 x lo"'-^),
cyanide ions are added in sufficient quantity to form the Fe(CN)6'^~ complex (Kf
= 1 X10^^) and dissolve the precipitate. Note that the iron (II) ion is involved in
the formation of the complex ion.
c. Write the balanced solubility equilibrium equation, complex ion formation
equation, and the overall equation.
* Formation constants obtained from Brown, LeMay, Burnsten (2006). Chemistry The Central Science
AP Edition. Pearson Education Canada, Inc. Toronto, Ontario, p. 750.