Solubility Equilibrium (Ksp)

•

Ksp Concept Overview

Negative Ions

Essentially All

Essentially All

Essentially All

Nitrate, NO3

Acetate, CH3COO

Chloride, Cl Bromide, Br Iodide, 1

Sulfate, so/

Sulfide, S

Hydroxide, OH

Phosphate, P04^ Carbonate, COB^

Sulfite, SOB^

Chromate, Cr04^

Solubility Chart

Positive Ions

Alkali ions (U\ Na% K\ Rb", Cs")

Hydrogen ion, H*

Ammonium ion, NH4*

Essentially All

Essentially All, EXCEPT Ag"

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 '

All others

Alkali ions and H\ NH4'

All others

Ba % Sr2^ Pb % Ag'

All others

Solubility

Soluble, (aq)

Soluble, (aq)

Soluble, (aq)

Soluble, (aq)

Soluble, (aq)

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)

Low Solubility, (s)

Soluble, (aq)

C8 Solubility Product Constants (AC J sp-

Solubility Product Constants at 25°C

Name

barium carbonate

barium chromate

barium sulfate

calcium carbonate

calcium oxalate

calcium phosphate

calcium sulfate

copperO] chloride

copperO] iodide

copperOO iodate

copperOO sulfide

ironOO hydroxide

ironOO sulfide

ironCIII) hydroxide

leadOO bromide

leadOD chloride

leadOD iodate

leadOD iodide

lead00 sulfate

magnesium carbonate

magnesium fluoride

magnesium hydroxide

mercuryO) chloride

silver bromate

silver bromide

silver carbonate

silver chloride

silver chromate

silver iodate

silver iodide

strontium carbonate

strontium fluoride

strontium sulfate

zinc hydroxide

zinc sulfide

Formula

BaC03f3)

BaCr04(s)

BaSO^cs)

CaC03f33

CaC204fs); CaOOCCOOfs)

Ca3(P0^2is)

CaS04(33

CuCI(33

Culfs)

cuao332Cs)

CuS(33

FeC0H)2Cs)

FeS(33

FeCOH33C33

PbBr2(33

PbCl2(s)

Pba0332(s)

Pbl2Cs)

PbSOz,cs)

MgC03f33

MgFacs)

MgC0H)2Cs)

Hg2Ci2(s)

AgBr03f33

AgBr(33

Ag2C03Cs3

AgCI(3)

Ag2Cr04(3)

Agi03cs3

Agi(s3

SrC03C33

SrF2(3)

SrS04C33

ZnCOH32(33

ZnSt33

'fsp

2.6 X 10^^

1.2 X 10^1°

1.1 X 10^1°

5.0 X 10"^

2.3 X 10"^

2.1 X 10~33

7.1 X 10-5

1.7 X 10"^

1.3 X 10^12

6.9 X 10"^

6.0 X 10-3^

4.9 X 10^^^

6.0 X 10"^^

2.6 X 10^33

6.6 X 10"^

1.2 X 10^5

3.7 X 10-^^3

8.5 X 10-9

1.8 X 10-«

6.8 X 10" ^

6.4 X 10-9

5.6 X 10-12

1.5 X 10-1^

5.3 X 10-5

5.4 X 10-13

8.5 X 10-12

1.8 X 10-1°

1.1 X 10-12

3.2 X 10-^

8.5 X 10-1^

5.6 X 10-10

4.3 X 10-9

3.4 X 10"^

7.7 X 10-1^

2.0 X 10-25

Values in this table are taken from The Physics, 76th Edition.

CRC Handbool< of Chemistry and

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.

B shaftesburychemistry.pbwiki.com S (204) 888-5898 ISJ Shaftesbury High School, 2240 Grant Ave, Wpg, MB, R3P 0P7

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 f luoride in mg in 200 . 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 00 . mL at 25°

C.

Calculating Ksp

Steps to calculate Ksp from solubility.

© S I . Wr i te balanced equilibrium equation.

© S2. Wr i te 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 25°C given that

0 .00172 g dissolves in 1 00 . 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. 20 mL 0.50 M K2Cr04 solution Distilled water

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 & fo lded fi l ter paper

3. 1 0 0 mL graduated cylinder

4. 150 mL beaker

5. 50 mL graduated cylinder

6. 50 mL beaker

7. glass stir rod

8. massed 250 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. 250 mL f i l t rate beaker

Ksp of PbCb Prelab

If 1.00 g of solid lead (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 add an ion, an entire solution containing the

common ion must be added 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 450. mL of solution.

Calculate the mass of iron (III) hydroxide that dissoves in mg in

450. 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 200 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 add a solution containing a common ion. In this case,

it has decreased by a factor of 1 O V 0'^^ = ] 00 0 0 0 000 !

This is simply a quantitative application of Le Chatelier's

Principle.

Common Ion Effect Conclusion

Predicting Precipitation p. 489 Q.5 a)

Wi 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

Wil l 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

Step 1. Write balanced equilibrium dissociation equation for the

precipitate using solubility rules.

solution? 1/ _ , - - ' o " ^

> = >

Predicting Precipitation Sample Problem 2

How to Solve Predicting Precipitation Questions

Step 1. Wr i te 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 added before Pb^+ ions precipitate?

What 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. 487

+

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 add lots of water, only if the Ksp of precipitate is around

10-3

2. Add a strong acid.

3. Make a complex ion by adding an excess of NH3, O H , HCI

4 . Make 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. Wri te 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 = 1.7x10"^).

^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 54 x 10" ^

a. Circle the precipitate that may be formed in order to dissolve a saturated solution of silver bromide. Explain your reasoning.

Formula

Ag2C03

AgBrOj

Agl PbBr2

Ksp

8.5x10" ' '

5.3 x io "^

8.5 X 10"'^

6.6x10"^

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.