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Solutions, Solubility, and Reaction Types

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

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Solutions, Solubility, and Reaction Types

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  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 = molvolume of solution L • Molality (m)= moles solute = molkg 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) = molvolume of solution L

  3. Mole Fraction • XA= nA/ total moles • Practice Problem

  4. Titration • - moles of acid= moles of base @ 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

  5. Dilution:(Minitial)(Vinitial) = (Mfinal)(Vfinal) 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? Minitial = (100.0 g NaOH)/(40.00 g/mol NaOH) = 5.00 M 0.500 L (Mi)(Vi) = (Mf)(Vf) = (5.00 M)(0.500 L) = (2.00 M)(Vf) Vf = 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 H2O molecules surround and separate ions from ionic crystal lattice • Molecular compounds:do not ionize because intramolecular bonds are stronger than bonds that form between H2O 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.http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/flashfiles/thermochem/solutionSalt.html(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 • http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::100%25::100%25::/sites/dl/free/0072512644/117354/07_Strong_Weak_Nonelectrolytes.swf::Strong%20Electrolytes,%20Weak%20Electrolytes,%20and%20Nonelectrolytes( electrolytes animation) • http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/flashfiles/electroChem/conductivity.html (Conductivity of different substances)

  8. 4.3: Acids & Bases • Bronsted-Lowry definitions: • Acids: H+ donor • Bases: H+ acceptor Group 1A’s: LiOH, NaOH, KOH, RbOH, CsOH Heavy 2A’s: Ca(OH)2, Sr(OH)2, Ba(OH)2 HBr, HCl, HI HNO3, H2SO4 HClO4, HClO3

  9. 4.4: Ionic Equations • Molecular equation: shows complete chemical equation with states of matter, undissociated BaCl2 (aq) + Na2SO4 (aq) → 2 NaCl (aq) + BaSO4 (s) • Complete ionic equation: shows complete chemical equation with states of matter, dissociated if appropriate Ba2+(aq) + 2 Cl-(aq) + 2 Na+(aq) + SO42-(aq) → 2 Cl-(aq) + 2 Na+(aq) + BaSO4 (s) • Spectator ions:present in reaction but do not “participate”; depend on solubility rulesCl- (aq) and Na+ (aq) http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/crm3s2_3.swf ( Precipitation Animation) 3. Net ionic equation:shows chemical equation without spectator ionsBa2+ (aq) + SO42- (aq) → BaSO4 (s)

  10. Solubility Rules (memorize them!) • Also, compounds with Group 1A and NH4+ cations

  11. Other anions (e.g., BrO3- or Cr2O72-) are generally insoluble except with the soluble cations (Group 1A and NH4+) • http://www.wisc-online.com/objects/ViewObject.aspx?ID=GCH2904

  12. AP Exam: Predicting Reaction Products Reactants: • Write all soluble ionic compounds, strong acids, and strong bases in aqueous solution as their constituent ions. Never write NaCl or Ca(NO3)2, HCl or HNO3, NaOH or Ba(OH)2, etc. Products: • Assume a reaction occurs. • Inspect all of the ions to see if any precipitates will form. • Cross out any spectator ions. • 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 • Dilute hydrochloric acid is added to a dilute solution of mercury (I) nitrate. • Dilute sulfuric acid is added to a solution of barium chloride. H+ + Cl- + Hg22+ + NO3-→ Hg2Cl2+ NO3- + H+ 2 Cl- + Hg22+ → Hg2Cl2 H+ + SO42- + Ba2+ + Cl- → BaSO4+ H+ + Cl- SO42- + Ba2+ → BaSO4

  15. Hydrogen sulfide gas is added to a solution of cadmium nitrate. • A scoop of silver nitrate is added to a solution of sodium chromate. H2S + Cd2+ + NO3- → CdS + H+ + NO3- H2S + Cd2+ → CdS + 2 H+ AgNO3+ Na+ + CrO42- → Ag2CrO4 + Na+ + NO3- 2 AgNO3+ CrO42- → Ag2CrO4 + 2 NO3-

  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+ + NO3-→ Cs+ + NO3- + H2O • H+ + OH-→ H2O • SO3 + H2O → H2SO4 • SO3 + H2O → 2 H+ + SO42- • Na2O + H2O → NaOH • Na2O + H2O → 2 Na+ + 2 OH-

  17. Nonmetal oxide + Metal oxide → Salt Ex: Solid calcium oxide is heated in the presence of sulfur trioxide gas. CaO + SO3 → CaSO4 If this were in water: CaO + H2O → Ca2+ + OH- and SO3 + H2O → H2SO4→ H+ + SO42- So, our overall reaction would be: Ca2+ + H2O + SO42- → CaSO4 + H2O But this can happen without water: CaO + SO3 → CaSO4

  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. K2O + H+ + Cl- →K+ + Cl- + H2O (K+ + O2-) + H+ + Cl- →K+ + Cl- + H2O K2O + 2 H+ →2 K+ + H2O CO2 + Ba2+ + OH-→ BaCO3+ H2O CO2 + Ba2+ + 2 OH- →BaCO3+ H2O

  19. Any suggestions for others you’ve seen on old/practice exams, let me know.

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