1. 1 Solutions, Solubility, and Reaction Types Brown, LeMay Ch 4 AP Chemistry

2. 2 4.1: Solutions & Expressing Concentration Solution: homogeneous mixture of 2 or more substances solute: component present in lesser quantity solvent: component present in greater quantity Molarity (M) =moles solute=mol volume of solution L Molality (m) =moles solute=mol kg of solvent kg *Normality (N): associated with acid & base strength = (moles solute)(# of acid/base equivalents) = mol volume of solutionL

3. 3 Dilution: (M initial )(V initial ) = (M final )(V final ) Ex: How much water must be added to a solution that contains 100.0 g NaOH in 500. mL of solution to make the final concentration 2.00 M? M initial = (100.0 g NaOH)/(40.00 g/mol NaOH) = 5.00 M 0.500 L (M i )(V i ) = (M f )(V f ) = (5.00 M)(0.500 L) = (2.00 M)(V f ) V f = 1.25 L, so 0.75 L water must be added.

4. 4 4.2: Properties of Solutes Ionic compounds (salts): dissociate in water by solvation, in which polar H 2 O molecules surround and separate ions from ionic crystal lattice Molecular compounds: do not ionize because intramolecular bonds are stronger than bonds that form between H 2 O and molecule Acids and bases, sometimes considered molecular (depending on strength), may also ionize.

5. 5 Electrolyte: substance which, in aqueous solution, ionizes and thus conducts electricity Non-electrolyte: substance which, in aqueous solution, does not dissociate and thus does not conduct electricity Strong & weak electrolytes: conductivity depends on degree of dissociation and equilibrium position: HA (aq) ↔ H+ (aq) + A- (aq) Strong = nearly completely dissociated Weak = partially dissociated

6. 6 4.3: Acids & Bases Bronsted-Lowry definitions: Acids: H + donor Bases: H + acceptor Figure 1: Strong & weak: depends on degree of dissociation (K a value, Table 4.1, p. 117) Strong AcidsStrong Bases HBr, HCl, HI HNO 3, H 2 SO 4 HClO 4, HClO 3 Group 1A’s: LiOH, NaOH, KOH, RbOH, CsOH Heavy 2A’s: Ca(OH) 2, Sr(OH) 2, Ba(OH) 2

7. 7 4.4: Ionic Equations 1. Molecular equation: shows complete chemical equation with states of matter, undissociated BaCl 2 (aq) + Na 2 SO 4 (aq) → 2 NaCl (aq) + BaSO 4 (s) 2. Complete ionic equation: shows complete chemical equation with states of matter, dissociated if appropriate Ba 2+ (aq) + 2 Cl - (aq) + 2 Na + (aq) + SO 4 2- (aq) → 2 Cl - (aq) + 2 Na + (aq) + BaSO 4 (s) Spectator ions: present in reaction but do not “participate”; depend on solubility rules Cl - (aq) and Na + (aq) 3. Net ionic equation: shows chemical equation without spectator ions Ba 2+ (aq) + SO 4 2- (aq) → BaSO 4 (s)

8. 8 Solubility Rules (memorize them!) Figure 2: Compounds that are always soluble. Compounds containing… Important Exceptions NO 3 - CH 3 COO - Cl -, Br -, I - SO 4 2- None Ag +, Hg 2 2+, Pb 2+ Ag +, Hg 2 2+, Pb 2+, Sr 2+, Ba 2+, Ca 2+ Also, compounds with Group 1A and NH 4 + cations

9. 9 Scene from The G Block Featuring 2003-04 AP Chemistry students Daniel Fong, Ashwin Nirmalkumar, Veselin Kolev, and Shintaro Funasaki. Cameo here by Rob Palmiotto.

10. Figure 3: Compounds that always insoluble. Compounds containing… Important Exceptions Other anions (e.g., BrO 3 - or Cr 2 O 7 2- ) are generally insoluble except with the soluble cations (Group 1A and NH 4 + ) CO 3 2-, CrO 4 2-, C 2 O 4 2- PO 4 3- OH - S 2- Group 1A, NH 4 + Group 1A, Sr 2+, Ba 2+, Ca 2+ Group 1A, NH 4 +, Sr 2+, Ba 2+, Ca 2+

11. 11 AP Exam: Predicting Reaction Products In general, when writing the reactants: 1. Write all soluble ionic compounds in aqueous solution as their constituent ions. Never write NaCl, Ca(NO 3 ) 2, etc. 2. Write all strong acids in water as H + or H 3 O + and the anion. Never write HCl, HNO 3, etc. 3. Write all strong bases as OH - and the cation. Never write NaOH, Ba(OH) 2, etc. 4. Don’t omit any ions unless absolutely sure that they are be spectator ions. For example, although the Cl - in HCl is usually a spectator ion, it is sometimes a reactant.

12. 12 In general, after writing the products: 1. Inspect all of the ions in the products to see if there are any precipitates. 2. Cross out any spectator ions. 3. Balance the reaction. Practice Predicting Precipitation Reactions Observations from previous AP exams: These types of reactions generally involve mixing two solutions, but may include the addition of hydrogen sulfide gas. Many involve formation of a single insoluble precipitate, but watch for the possibility of two insoluble products.

13. 13 Examples A.Dilute hydrochloric acid is added to a dilute solution of mercury (I) nitrate. B.Dilute sulfuric acid is added to a solution of barium chloride. H + + Cl - + Hg 2 2+ + NO 3 - → Hg 2 Cl 2 + NO 3 - + H + H + + SO 4 2- + Ba 2+ + Cl - → BaSO 4 + H + + Cl - 2 Cl - + Hg 2 2+ → Hg 2 Cl 2 SO 4 2- + Ba 2+ → BaSO 4

14. 14 C.Hydrogen sulfide gas is added to a solution of cadmium nitrate. D.Solutions of silver nitrate and sodium chromate are mixed. H 2 S + Cd 2+ + NO 3 - → CdS + H + + NO 3 - Ag + + NO 3 - + Na + + CrO 4 2- → Ag 2 CrO 4 + Na + + NO 3 - 2 Ag + + CrO 4 2- → Ag 2 CrO 4 H 2 S + Cd 2+ → CdS + 2 H +

15. 15 Other reactions to know: Acid + Base → Salt + Water Ex: A solution of cesium hydroxide is added to a solution of nitric acid. Nonmetal oxide + Water → Oxyacid Ex:Sulfur trioxide gas is added to excess water. Metal oxide + Water → Base Ex:Solid sodium oxide is added to water. Cs + + OH - + H + + NO 3 - → Cs + + NO 3 - + H 2 O H + + OH - → H 2 O SO 3 + H 2 O → H 2 SO 4 SO 3 + H 2 O → 2 H + + SO 4 2- Na 2 O + H 2 O → NaOH Na 2 O + H 2 O → 2 Na + + 2 OH -

16. 16 Nonmetal oxide + Metal oxide → Salt Ex: Solid calcium oxide is heated in the presence of sulfur trioxide gas. CaO + SO 3 → CaSO 4 If this were in water: CaO + H 2 O → Ca 2+ + OH - and SO 3 + H 2 O → H 2 SO 4 → H + + SO 4 2- So, our overall reaction would be: Ca 2+ + H 2 O + SO 4 2- → CaSO 4 + H 2 O But this can happen without water: CaO + SO 3 → CaSO 4

17. 17 Metal oxide + Acid → Salt + Water Ex:Potassium oxide solid is added a solution of hydrochloric acid. Nonmetal oxide + Base → Salt + Water Ex:Carbon dioxide is bubbled through a solution of barium hydroxide. K 2 O + H + + Cl - → K + + Cl - + H 2 O (K + + O 2- ) + H + + Cl - → K + + Cl - + H 2 O K 2 O + 2 H + → 2 K + + H 2 O CO 2 + Ba 2+ + OH - → BaCO 3 + H 2 O CO 2 + Ba 2+ + 2 OH - → BaCO 3 + H 2 O

18. Ion(aq) Co 2+ [CoCl 4 ] 2- Rose Blue Cr 3+ CrO 4 2- Cr 2 O 7 2- Green Yellow Orange Cu 2+ [Cu(NH 3 ) 4 ] 2+ Light blue Medium blue Fe 2+ Fe 3+ [Fe(SCN)] 2+ Green Yellow-brown Red Mn 2+ Pink Ni 2+ Green Grp I-A + Grp II-A 2+ Al 3+ Colorless Zn 2+ Colorless or “milky”

19. CompoundsColor PbI 2 Grp I-A + /II-A 2+ & CrO 4 2- Yellow Grp I-A + /II-A 2+ & Cr 2 O 7 2- Orange AgX Grp I-A + /II-A 2+ & NO 3 -, C 2 H 3 O 2 -, X -, SO 4 2- White AgNO 3 White, turns black in sunlight CuOGreen Fe 2 O 3 Rust KMnO 4 Purple HgODark red NO 2 (g)Brown Any suggestions for others you’ve seen on old/practice exams, let me know.