Catalyst Complete the exam reflection End

The Month Ahead! Final Unit! S Monday Tuesday Wednesday Thursday Friday 4 5 Lab Report Due! 6 7 8 9 10 11 12 13 14 Electro. Lab 15 16 Saturday School 17 18 Review 19 20 21 Unit 8 Exam 22 SPRING BREAK!

Teeth in Soda/Coffee Tooth enamel (Ca10(PO4)6), the hardest substance in the body, dissolves in acidic solutions, for example, causing tooth decay, and the precipitation of certain salts in our kidneys produces kidney stones Tooth enamel does not dissolve in basic solutions

Justify – TPS Why does tooth enamel, Ca10(PO4)6(OH)2, decay in acidic solutions, but not in basic solutions?

Lecture 8.1 – Common Ion Effect and Ksp

Today’s Learning Targets LT 8.1 – I can explain the common ion effect and how it impacts the overall ionization of a compound that is in equilibrium. LT 8.2 – I can write a Ksp for slightly soluble salts LT 8.3 – I can calculate the Ksp and equilibrium concentrations from initial concentration and/or solubility data. LT 8.5 – I can explain and calculate, using the Ksp, how the solubility of a compound is influenced by both the common ion effect and pH.

Precipitation Reaction Many reactions results in the production of a solid compound know as a precipitate. These reactions are known as precipitation reactions. We can determine whether or not a solid will form based on a few rules. 2KI + Pb(NO3)2  2KNO3 + PbI (s) PbNO3 reaction

Solubility Rules The solubility of a compound is determined by the ions a compound contains: All group I and ammonium ions are soluble All nitrate, acetate, and chlorate compounds are soluble All binary compounds of halogens (other than F) with metals are soluble, except those of Ag, Hg (I) and Pb. All sulfate containing compounds are soluble, except those of barium, strontium, calcium, lead, silver, and mercury Except for rule 1, all carbonate, hydroxide, oxide, silicate, and phosphate containing compounds are insoluble Sulfide containing compounds are insoluble, except for those with calcium, barium, strontium, magnesium, sodium, potassium, and NH4+

Soluble Ionic Compounds Exceptions Compounds Containing NO3- None CH3COO- Cl- Compounds of Ag+, Hg2+, Pb2+ Br- I- SO42- Compounds of Sr2+, Ag+, Hg2+, Pb2+ Insoluble Ionic Compounds S2- Compounds of NH4+, the alkali metal cations, Ca2+, Sr2+, Ba2+ CO32- Compounds of NH4+ and the alkali metal cations. PO42- OH-

Class Example Identify the compounds that soluble and the ones that are insoluble: Na2CO3 PbSO4

Table Talk Identify the compounds that soluble and the ones that are insoluble: Co(OH)2 Ba(NO3)2

Solubility Product Constant (Ksp) A saturated solution is one that has dissolved as much solid as possible. In a saturated solution, equilibrium is established: BaSO4 (s) ⇌ Ba2+ (aq) + SO42- (aq) The equilibrium constant for slightly soluble salts is known as the solubility – product constants or Ksp Ksp = [Ba2+]1[SO42-]1

Class Example Write the Ksp expression for calcium fluoride

Table Talk Write the solubility – product constant (Ksp) for silver sulfate

Ksp Solubility and Ksp Solubility of compound (g/L) The Ksp is NOT the solubility Solubility describes how many grams can dissolve in a liter of solution The Ksp describes how much dissolves to form a saturated solution Solubility can change, but Ksp CANNOT Ksp Solubility of compound (g/L) Solubility Equilibrium Molar Mass Compound Formula Molar Solubility of compound (mol/L) Ion Concentration (mol/L)

Class Example Solid silver chromate is added to pure water at 25 oC, and some of the solid remains undissolved. The mixture is stirred for several days to ensure that equilibrium is achieved between the undissolved Ag2CrO4 (s) and the solution. Analysis of the equilibrated solution. Analysis of the equilibrated solution shows that its silver ion concentration is 1.3 x 10-4 M. Calculate the Ksp for the solution

Table Talk A saturated solution of Mg(OH)2 in contact with undissolved Mg(OH)2 is prepared at 25 oC. The pH of the solution is found to be 10.17. Assuming that Mg(OH)2 dissociates completely in water, calculate Ksp for this equilibrium. HINT – Think Kw…

Class Example The Ksp for CaF2 is 3.9 x 10-11 at 25 oC. Assuming that CaF2 dissociates completely upon dissolving and that there are no other important equilibria affecting its solubility, calculate the solubility of CaF2 in grams per liter.

Table Talk The Ksp for LaF3 is 2 x 10-19. What is the solubility of LaF3 in moles per liter?

Talking it to the Next Level! Based on your current level, attempt the questions around the classroom. Pink – Cake Walk Level Yellow – Heating Up Level Blue – Expert Chemist Questions

Fluoridation of Water Supply Tap water contains fluoride ions in order to help prevent cavities. Fluoridinated water replaces the OH group on tooth enamel with a fluoride ion. The Ksp of normal tooth enamel (Ca10(PO4)6(OH)2) is 6.8 x 10-37 The Ksp of tooth enamel with OH group replaced Ca10(PO4)6F2 is 5.0 x 10-51.

Justify – TPS The Ksp of normal tooth enamel (Ca10(PO4)6(OH)2) is 6.8 x 10-37 The Ksp of tooth enamel with OH group replaced Ca10(PO4)6F2 is 5.0 x 10-51. Why do you think adding fluoride to water is crucial to lowering the amount of cavities we have as a country?

Factors that Impact Solubility There are three ways in which solubility of slightly soluble salts can be impacted: 1. Common Ion Effect 2. The pH of Solution 3. Presence of Complexing Agent

Common Ion Effect Recall the acetate equilibrium: CH3COOH ⇌ H+ + CH3COO- If we had both acetic acid and acetate in solution, than the acetic acid will ionize less in order to achieve equilibrium. Very little movement needs to be done in order to achieve equilibrium. Whenever a weak electrolyte and a strong electrolyte containing a common ion are together, the weak electrolyte ionizes less than when it is alone in solution This is known as the common ion effect

Class Example Calculate the molar solubility of CaF2 that is in a solution of 0.010 M Ca(NO3)2. NOTE – The Ksp for CaF2 is 3.9 x 10-11 The typical molar solubility of CaF2 is 2.1 x 10-4 M…notice how much lower it is now that we added one of the ions to the equilibrium.

Table Talk For manganese (II) hydroxide the Ksp is 1.6 x 10-13. Calculate the molar solubility of manganese (II) hydroxide in a solution that contains 0.020 M NaOH

Mg(OH)2 (s) ⇌ Mg2+ (aq) + 2 OH- (aq) Ksp = 1.8 x 10-11 pH and Solubility The pH of a solution impacts the solubility for any compound that has a basic component when dissolved in solution Consider the equilibrium: Mg(OH)2 (s) ⇌ Mg2+ (aq) + 2 OH- (aq) Ksp = 1.8 x 10-11 If we are in a basic solution, then we will have more solid due to the presence of extra hydroxide ions The solubility of a compound containing a basic component increases as the pH is lowered.

Class Example Which of these substances are more soluble in acidic solution than in basic solution: (1) Ni(OH)2 (2) CaCO3 (3) BaF2 (4) AgCl

Table Talk Which of these substances are more soluble in acidic solution than in a neutral solution: (1) ZnCO3 (2) ZnS (3) BiI3 (4) AgCN (5) Ba3(PO4)2 All except BiI3

White Board Problems

BaF2 (s) ⇌ Ba2+ (aq) + 2 F- (aq) White Board Problems The molar solubility of Ag2SO4 is 0.014 M at 25 oC. Based on this information, what is the value of Ksp for Ag2SO4 The value of the solubility product constant for the reaction: BaF2 (s) ⇌ Ba2+ (aq) + 2 F- (aq) Is 1.1 x 10-6. Calculate the concentration of F- ions in a saturated solution of BaF2 500 mL of a 0.0050 molar NaF solution is added to 400 mL of a 0.0050 molar Ba(NO3)2 solution. Will there be a precipitate? Use the equilibrium from the previous problem.

Exit Slip 1. Calculate the molar solubility of a pure solution of CaF2. The Ksp of CaF2 is 3.9 x 10-11. 2. Calculate the molar solubility of CaF2 that is in a solution of 0.010 M Ca(NO3)2. NOTE – The Ksp for CaF2 is 3.9 x 10-11. Discuss how this answer in #1 and #2 demonstrates the impact the common ion effect has on the dissociation of a slightly soluble salt

Rate Yourself! Rate yourself 1 – 4 on LTs 8.1, 8.2, 8.3, and 8.5

Closing Time Read 17.1, 17.4, and 17.5 Homework: HW 8.1