Solubility Equilibrium (Ksp)

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Ksp Concept Overview

Solubility Equilibrium.092.notebook

May 2­8:29 AM

This is a saturated solution of PbCl2.

Sketch the particulate diagram of the solution.Include relative sizes and numbers of ions and the interaction of water with at least one positive ion and one negative ion. Label each particle with its element symbol and charge, if necessary.

Calculate the concentrations of Pb2+ and Cl- ions in solution at 25°C.

Calculate the solubility of PbCl2 in grams in 1.5 L.

1.

2.

3.

Pb2+

Cl-

OHH

Solubility Equilibrium Interactive Simulation

Shaftesbury High School | 2240 Grant Ave., Winnipeg, MB | 204.888.5898 | www.pembinatrails.ca/shaftesbury

Objectives

1. To compare the solubility of various soluble ionic compounds.

2. To examine the concentrations of various solutions at saturation.

3. To compare Ksp values of soluble ionic compounds with Ksp values of ionic compounds with low

solubility.

Procedure

1. Run the Concentration simulation at

http://phet.colorado.edu/sims/html/concentration/latest/concentration_en.html. The

following screen should appear.

2. Familiarize yourself with the simulation by varying the type of solute, the amount of water, the

rate of evaporation, etc…

Data Collection and Calculations

3. Calculate the molar mass of each compound and record the results in Table 1.

4. Record the concentration at saturation of each solution in the table.

Solubility Equilibrium Interactive Simulation

Shaftesbury High School | 2240 Grant Ave., Winnipeg, MB | 204.888.5898 | www.pembinatrails.ca/shaftesbury

5. Calculate the solubility of each solution in grams per litre. Show your calculations for one of the

solutions below. They should follow a logical mathematical sequence, including proper units

and significant figures.

6. Calculate the solubility product constant, Ksp, of any solution with a 2:1 or 1:2 ratio of cation to

anion. Show complete calculations in the space below, including proper units and significant

figures.

Table 1. Solubility Equilibrium Data for Eight Solutions of Ionic Compounds

Substance Chemical Formula

Molar Mass (g/mol)

c at Saturation

Solubility in g/L

Ksp

1. Drink Mix 2. Cobalt (II)

Nitrate Co(NO3)2

3. Cobalt (II) Chloride

CoCl2

4. Potassium Dichromate

K2Cr2O7

5. Potassium Chromate

K2CrO4

6. Nickel (II) Chloride

NiCl2

7. Copper (II) Sulfate

CuSO4

8. Potassium Permanganate

KMnO4

Questions

6. How does the concentration of a saturated solution change as more solvent evaporates?

7. Why are none of these solutions found in Ksp tables?

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

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)

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

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 Problem Set: Solubility Equilibrium

1. Calculate the Ksp of iron (III) hydroxide if 1.60 x 10-6 mg dissolves in 150 mL of solution. (2)

2. A. Calculate the solubility in mg of calcium phosphate in 200 mL of pure water. Use

tables for Ksp. (2) B. Calculate the solubility in mg of calcium phosphate after 0.20 M of sodium

phosphate is added to 200 mL of solution. (2) C. What happens to the solubility of an ionic compound with the addition of a

common ion? (1)

3. Will a precipitate form if 15 mL of 0.15 M Pb(NO3)2 is mixed with 100. mL of 0.10 M

NaI? Show all of your work for full marks. (3)

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Chemistry 40S/40SH Lab Practicum

Student:________________ Student:__________________ Student:_________________

OBJECTIVE

In groups determined by the instructor design and conduct an experiment to …

Determine the Ksp of a saturated solution of PbCl2 using 100.0 mL of saturated PbCl2(aq) and 20.0 mL of 0.50 M K2CrO4(aq).

TIMELINE

Day 1: Student groups collaborate and submit one copy of each of the following to the instructor for grading:

1. A stepwise description of the complete laboratory procedure, including sketches. Sketches must be labelled and embedded in the procedure.

2. An outline of the stepwise sequence of calculations that must be performed to arrive at the

intended result, including balanced equations, the Ksp expression, and units. Use Ksp calculations from Ksp of PbCl2 prelab to develop the sequence.

Day 2: Students perform and complete the lab according to their procedure and submit their results for grading.

CHEMICALS & EQUIPMENT

The following equipment may be used to fulfil the lab objective. Other materials may be sanctioned by the instructor upon request by student groups.

safety goggles distilled water

wash bottle 50 & 100 mL

graduated cylinders Glass stir rod

massed & folded filter paper

Plastic funnel 50 & 250 mL

beakers Funnel clamp &

stand

Chemistry 40S/40SH Lab Practicum

Student:________________ Student:__________________ Student:_________________

Lab Practicum Assessment Rubric

Criteria Developing

(0 — 1 mark) Intermediate

(2 marks) At Level

(3 marks)

Procedure

Procedure is missing significant information such that a high level of

intuition or experience in chemistry is necessary to interpret the information and successfully conduct

the experiment (1) or there is no chance that the

procedure is useful enough to attain the objective (0)

Aspects of the procedure (including labeled sketches)

are missing, out of sequence, or incorrect but

procedure is complete enough that it is likely a

skilled chemistry student could still conduct the

experiment; accuracy of results may be compromised

Procedure follows a logical sequence, includes labeled sketch(es) of the

laboratory setup, and is complete to the

extent that any chemistry student may

successfully conduct the experiment

Calculations

Results contain less than Intermediate level

assessment criteria (1) or no calculations presented

(0)

Calculations are communicated, but some

aspect is incomplete, incorrect, or otherwise

unclear

All required calculations are clearly

listed in a logical sequence, including

correct balanced equations, the Ksp

expression, and units

Results

Results are not submitted (0) or are incorrect to the

extent that a final Ksp value is not calculated (1)

Sequencing of calculations is incomplete or incorrect.

Complete and correctly calculated results are submitted following

the sequence of calculations developed

on Day 1

Student Collaboration & Efficiency

Less than intermediate criteria

the student’s contribution was less than an equitable portion of the total group’s collaboration or the student

collaborated with little consideration to efficiency

The student contributed equitably

to the group objectives, assuming

and completing a critical role in an

efficient manner over the entire two days

/12

Ksp of PbCb Prelab

If 1.00 g of solid lead (II) chromate precipitates, calculate the

Ksp of PbCb.

Chemistry 40S Solubility Equilibrium Practice Quiz

Particulate Diagram

Saturated Solution of Ca(OH)2 at 25°C

1. In the flask to the left, sketch a particulate diagram of each of the components in solution, including water molecules. Pay attention to relative size and number of each ion. Show the interaction of water molecules with at least one positive ion and one negative ion. Each particle should be labelled with the appropriate element symbol and ion charge. (2)

Useful resource: http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/crm3s2_3.swf

Interpreting Ksp Values

2. Which saturated solution in equiliibrium has the greatest solubility at 25°C? (1)

A. Barium chromate B. Silver carbonate C. Zinc hydroxide D. Copper (I) iodide 3. Which compound has the lowest concentration of ions in solution at 25°C? (1)

A. BaCrO4 B. Mg(OH)2 C. CuCl D. SrSO4

Chemistry 40S Solubility Equilibrium Practice Quiz

Solubility from Ksp data (molar solubility & other units—mg, g/L, etc…)

4. Calculate the molar solubility in mol/L of silver bromate at 25°C. (2)

5. Calculate the solubility of 500.0 mL of a saturated solution of ZnS at 25°C in milligrams. (3)

Ksp from solubility data

6. Calculate the solubility product constant, Ksp, of Bi2S3 at 25°C if its molar solubility is 1.0 x 10–15 mol/L. (2) (Zumdahl, 2000, p.760)

Common ion effect

7. Calculate the molar solubility of solid CaF2 (Ksp = 4.0 x 10–11) in a 0.025 M NaF solution at 25°C. (2) (Zumdahl, 2000, p.764)

Chemistry 40S Solubility Equilibrium Practice Quiz

Predicting Precipitation (comparing Q to Ksp)

8. Will a precipitate form when 750.0 mL of 0.0040 M Ce(NO3)3 is added to 300.0 mL of 0.020 M KIO3? Ksp of the insoluble precipitate is 1.9 x 10–10. (3) (Zumdahl, 2000, p.766)

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