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Unit 4 (Chapter 4) : Aqueous Reactions & Solution Stoichiometry

Unit 4 (Chapter 4) : Aqueous Reactions & Solution Stoichiometry

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Unit 4 (Chapter 4) : Aqueous Reactions & Solution Stoichiometry

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  1. Chemistry, The Central Science, 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten Unit 4 (Chapter 4):Aqueous Reactions & Solution Stoichiometry John D. Bookstaver St. Charles Community College St. Peters, MO  2006, Prentice Hall, Inc.

  2. Solutions: + • homogeneousmixtures: evenlymixed (same) • solvent is present in greatest abundance. • solutedissolvedin/by solvent

  3. Molarity Molarity (M) is a measure of the concentration of a solution. moles of solute(mol) Molarity (M) = liters of solution(L) units: mol/L or mol∙L–1 What’s the concentration of a solution with 29.2 g of sodium chloride in 250. mL of water? 1 mol NaCl 58.44 g NaCl 2.00 M NaCl 0.500 mol NaCl = = 29.2 g NaCl x 0.250 L

  4. Solution Prep from Solid 1-Calc & Masssolute 2-Add solvent, swirl to dissolve 3-Fill with DI water to mark 4-Mix (Cap & Invert to mix evenly) WS #1-2 Conc. Calc’s

  5. WS Concentration & Dilutions #1 1 mol NaHCO3 84.01 g NaHCO3 1 L NaHCO3 x = 5.00 g NaHCO3x 0.100 mol NaHCO3 0.595 L NaHCO3 #2 1.20 mol CuSO4 1 L CuSO4 159.62 g CuSO4 x = 0.275 L CuSO4x 1 mol CuSO4 52.7 g CuSO4

  6. Solution Prep by Dilution 1-CalcM1V1=M2V2 2-Pipet V1 from concentrated 3-Fillto mark with DI water 4-Mix (Cap & Invert to mix evenly) M1V1 = M2V2 WS #3-4 Dilutions

  7. WS Concentration & Dilutions M1V1 = M2V2 HWp.160 #60, 67 M1V1 = M2V2 #3 (12.0 M)V1= (1.25 M)(500. mL) V1= 52.1 mL (or 0.0521 L) #4 M1V1 = M2V2 (2.50 M)V1= (0.200 M)(250. mL) V1= 20.0 mL (or 0.0200 L)

  8. + H – H O Cl O Cl H H H H • Acid: proton (H+) donor • Base: proton (H+) acceptor HCl + H2O  H3O+ + Cl– NH3 + H2O  NH4+ + OH– + H – H N O N O H H H H H H H H

  9. Strength of Acids and Bases STRONG: (complete ionization) (completely as ions) HA(aq)H+(aq)+ A–(aq) MOH(aq)M+(aq)+ OH–(aq) WEAK: (partialionization) (mostly as molecules) HA(aq)+ H2O(l) H3O+(aq)+ A–(aq) B(aq)+ H2O(l) BH+(aq)+ OH–(aq)

  10. Strong Acids: HI + H2O  H3O+ + I– proton (H+) donors Only 6 strong acids: • Nitric(HNO3) • Sulfuric(H2SO4) • Hydrochloric(HCl) • Hydrobromic(HBr) • Hydroiodic(HI) • Perchloric(HClO4)

  11. Strong Bases: OH–+ H3O+ H2O + H2O proton (H+) acceptors The strong basesare soluble hydroxides(OH–) of… • Group 1 (Li,Na,K) • CBS (Ca, Ba, Sr) Mg(OH)2& Be(OH)2 are not soluble Hydroxides of Group I and CBS ase

  12. Salts: Ionic Solids: (metal-nonmetal) dissociate (dissolve) by separation into ions Electrolytes: ions in solution that conduct electricity

  13. Non Weak Strong C11H22O11 CH3OH H2O NaOH HNO3 KCl CH3COOH HNO2 NH3 SOME ions NO ions ALL ions onlymolecules partiallyionize completely dissociate HW p.159 #33

  14. Electrolytes:Strong, Weak, or Non? (ions conduct electricity) HWp.157 #1,2,4,5,38 Compound metal-nonmetal nonmetals (Covalent) Ionic Molecular Acid (H____) Not Acid Weak Base STRONG KBr CaI2 FeCl3 NaOH Ca(OH)2 (strong bases) STRONG (6) WEAK NON (& NH3) C11H22O11 C2H5OH H2O CH3COOH HNO2 HF HCl, HBr, HI HNO3 H2SO4 HClO4

  15. QUIZ!!! (at the bell) Electrolytes:Strong, Weak, or Non? Compound metal-nonmetal nonmetals (Covalent) Ionic Molecular Acid (H____) Not Acid Weak Base STRONG STRONG (6) WEAK NON (& NH3)

  16. Acid-Base NeutralizationReactions • strong base (M+OH–) ionic compound (M+A–) water H2O (HOH) strong acid(H+A–) ACID + BASESALT + WATER + – O Cl Cl Na Na H O H H H • HCl(aq)+ NaOH(aq)NaCl(aq) + H2O(l) HWp.158 #40a

  17. PrecipitationReactions Double Replacement: (precipitate) 2 KNO3(aq)+PbI2(s) 2 KI(aq)+Pb(NO3)2(aq) • precipitate: • insoluble product • (as predicted by solubility rules) Pb2+ I–

  18. Solubility Rules ALWAYS Solubleions: Li+,Na+, K+, ... Group I (alkali metals) NH4+ammonium NO3–nitrate * * * Common Precipitates form with: examples Ag+, Pb2+, Hg2+(AP/H) AgCl, PbI2 OH–(hydroxide) Cu(OH)2 CO32–(carbonate) CaCO3 WSSolubility & NIE’s #1

  19. reactants and products in molecular form AgNO3(aq)+ KCl(aq) AgCl(s) + KNO3(aq) Molecular Equation Ionic Equation • Strong Electrolytesare Dissociatedas ions (strong acids, strong bases, soluble salts) Ag+(aq) + NO3–(aq) + K+(aq) + Cl–(aq)  AgCl(s) + K+(aq) + NO3–(aq)

  20. Ag+(aq) + NO3–(aq) + K+(aq) + Cl–(aq)  AgCl(s) + K+(aq) + NO3–(aq) NetIonic Equation (NIE) • Cross outSpectator Ions (no change) • onlyspecies leftare those that react(change) during the course of the reaction. (same state) (same charge) Net NIE: Ag+(aq) + Cl–(aq)  AgCl(s)

  21. BalancedNet Ionic Equations comp – diss – cross – net – bal • Write a Completemolecular equation. • Dissociateall strong electrolytes(aq) . • Cross outspectators (same charge & state) • Write the Net ionic equationwith the species that remain. • Balance the NIE. (solubility rules)

  22. BalancedNetIonic Equations comp – diss – cross – net – bal + 2– 2+ – + – • (NH4)2SO4 + Ba(NO3)2 → • NaOH + MgBr2 → BaSO4 + NH4NO3 Ba2+ + SO42– → BaSO4 + – 2+ – + – NaBr + Mg(OH)2 Mg2+ + 2 OH– → Mg(OH)2(s) HWp.158 #21

  23. H+ + OH– H2O Neutralization Reactions When a StrongAcidreacts with a StrongBase, the net ionic equation is… HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) H++ Cl–+ Na++ OH– Na++ Cl–+ H2O

  24. HX + OH– X– + H2O Neutralization Reactions When a Weak acidreacts with a Strong base, the net ionic equation is… HF(aq)+ KOH(aq) KF(aq)+ H2O(l) HF+ Na++ OH– Na++ F–+ H2O (dissociate ONLYSTRONG electrolytes) HWp.159 #40 (finish)

  25. BalancedNetIonic Equations comp – diss – cross – net – bal + 2– 2+ – + – (NH4)2SO4 + Ba(NO3)2 → BaSO4 + NH4NO3 Ba2+ + SO42– → BaSO4(s) + – + – HF(aq)+ KOH(aq) KF(aq)+ H2O(l) HF + OH– F– + H2O WSSolubility & NIE’s #2

  26. Gas-Forming Reactions H2Demo (M0) (H+) (M+) (gas) 2+ 2– + 2– Single Rep: Metal + Acid Metal Ion + H2 Ex: Zn(s)+ H2SO4(aq)ZnSO4(aq) + H2(g) NIE: Zn(s) + 2 H+(aq) Zn2+(aq) + H2(g) Double Rep: Acid + Carbonate Salt + Ex: HCl(aq) + CaCO3(s)CaCl2(aq) + H2O(l) + CO2(g) NIE: 2 H+(aq) + CaCO3(s) Ca2+(aq) + H2O(l) + CO2(g) (gas) H2O(l)+ CO2(g) (H+) (CO32–) CO2Demo H2CO3(aq) (orBicarbonate) (HCO3–) (decomposes immediately) HW p. 159 #43 CH3COOH + NaHCO3 CH3COONa + H2O + CO2

  27. Solution Stoichiometry Rxn: A(aq) + 2 B(aq) C + 2 D molar mass A molarity A (M) g A mol A L of A g A 1 mol A mol A 1 L mol-to-mol ratio HW p. 161 #81 mol B 1 L g B 1 mol B molarity B (M) molar mass B mol B L of B g B

  28. Oxidation-Reduction Reactions(REDOX) video clip (One cannot occur without the other) LEO saysGER

  29. Oxidation Numbers Is it a redox reaction? To find out… • assignoxidation numbers*(or oxidation states) to each element in a reaction. • check if any oxidation states changed (↓ reduced , ↑ oxidized) *charges of ionsshowelectronstransferredIN an ionic compound in Na2O, O2– *oxidation numbers of elements describe electronsthat would be lostor gainedIFthe compound was 100% ionic. in H2O, O–2

  30. Assigning Oxidation Numbers • All pureelements are 0 • Monatomic ion is its charge (Mg2+ has +2) • Most nonmetalstend to be negative, butsome are positive in certain compounds or ions. • Ois −2always • His +1 with nonmetals, −1withmetals (in SO3 , O is –2 but S is +6) but in peroxide ionis −1 (O22–) • Fis always −1. • otherhalogensare −1, BUTcan be positive, like in oxyanions. Ex. ClO3– or NO3– or SO42–

  31. Oxidation Numbers • The sumof the ox. #’s in a neutralcompound is 0. • The sum of the ox. #’s in a polyatomic ion is the charge on the ion. Determine the oxidation number of: Sulfur in… SO2 Chromium in… K2Cr2O7 Nitrogen in… NH4+ Cobalt in… [CoCl6]3–

  32. Classifying REDOX Reactions All rxns (but…NOT double replacement) Synthesis A + B →AB 2 → 1 (0 0 → +/–) Decomposition AB →A + B 1 → 2 (+/– →0 0) Single Replacement AB + C →A + CB (+/– 0 → 0 +/–) Combustion CxHy + O2→ CO2 + H2O (–/+ 0 →+/– +/–)

  33. Single Replacement (REDOX) Cu(s) + 2 Ag+(aq) Cu2+(aq)+ 2 Ag(s) silver ions oxidize copper metal X Cu2+(aq) + 2 Ag(s) Cu(s) + 2 Ag+(aq)

  34. Activity Seriesof Metals increasing ease of oxidation Cannotdisplace H+ from acid to make H2(g)

  35. Writing REDOX Reactions Write the net ionic equation for the reaction of solid zincin a solution of hydrochloric acid. comp – diss – cross – net – bal 0 +1 –1 +2 –1 0 Mg(s) + HCl(aq) MgCl2(aq) + H2(g) Mg + H+ Mg+2+ H2 2 Classify the reaction in two ways. Single-Replacement and Redox

  36. ox Mg + 2 H+ Mg2+ + H2(g) red What is red & what is ox? WSAq Soln’s & Chem Rxns