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

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. Normality = molarity x n (where n = the number of protons exchanged in a reaction). = (moles solute)(# of acid/base equivalents) = mol volume of solutionL

Mole Fraction X A = n A / total moles Practice Problem 3

Titration - moles of acid= moles of the end point -use stoichiometry to find other reactant/product moles M1V1= M2 V2 (sometimes used to get moles, M= moles/L, so moles= M XV) -What other ways can you get the moles- for a solid? For a gas? -color change by indicator indicates end point -end point and equivalence points should be close 4

5 Dilution: (M initial )(V initial ) = (M final )(V final ) Ex: How much water must be added to a solution that contains 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 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.

6 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.

7 Electrolyte: substance which, in aqueous solution, ionizes and thus conducts electricity. Ex: salt in water. (salt dissolving in water) 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 hill.com/olcweb/cgi/pluginpop.cgi?it=swf::100%25::100%25::/sites/dl/free/ /117354/07_Strong_Weak_Nonelectrolytes.swf::Strong%20Electrolytes,%20Weak%20Electrolyte s,%20and%20Nonelectrolyteshttp://highered.mcgraw- hill.com/olcweb/cgi/pluginpop.cgi?it=swf::100%25::100%25::/sites/dl/free/ /117354/07_Strong_Weak_Nonelectrolytes.swf::Strong%20Electrolytes,%20Weak%20Electrolyte s,%20and%20Nonelectrolytes ( electrolytes animation) (Conductivity of different substances)

8 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

9 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) ( Precipitation Animation) 3. Net ionic equation: shows chemical equation without spectator ions Ba 2+ (aq) + SO 4 2- (aq) → BaSO 4 (s)

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+ Hg 2 2+, Pb 2+, Sr 2+, Ba 2+, Ca 2+ Also, compounds with Group 1A and NH 4 + cations

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- S 2-, O 2-, OH- Alkali metals, NH 4 + Alkali metals, NH 4 +, Sr 2+, Ba 2+, Ca 2+

12 AP Exam: Predicting Reaction Products Reactants: 1. Write all soluble ionic compounds, strong acids, and strong bases in aqueous solution as their constituent ions. Never write NaCl or Ca(NO 3 ) 2, HCl or HNO 3, NaOH or Ba(OH) 2, etc. Products: 1. Assume a reaction occurs. 2. Inspect all of the ions to see if any precipitates will form. 3. Cross out any spectator ions. 4. Balance the reaction (and states of matter are not needed.)

13 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 or hydrogen chloride gas. Many involve formation of a single insoluble precipitate, but watch for the possibility of two insoluble products.

14 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 NO 3 - → Hg 2 Cl 2 + NO H + H + + SO Ba 2+ + Cl - → BaSO 4 + H + + Cl - 2 Cl - + Hg 2 2+ → Hg 2 Cl 2 SO Ba 2+ → BaSO 4

15 C.Hydrogen sulfide gas is added to a solution of cadmium nitrate. D.A scoop of silver nitrate is added to a solution of sodium chromate. H 2 S + Cd 2+ + NO 3 - → CdS + H + + NO 3 - AgNO 3 + Na + + CrO 4 2- → Ag 2 CrO 4 + Na + + NO AgNO 3 + CrO 4 2- → Ag 2 CrO NO 3 - H 2 S + Cd 2+ → CdS + 2 H +

16 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 Therefore, nonmetal oxides are called acid anhydrides. Ex:Sulfur trioxide gas is added to excess water. Metal oxide + Water → Base Therefore, metal oxides are called basic anhydrides. Ex:Solid sodium oxide is added to water. Cs + + OH - + H + + NO 3 - → Cs + + NO 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 OH -

17 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

18 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 OH - → BaCO 3 + H 2 O

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”

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.