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Unit # 4: Aqueous Reactions and Solution Stoichiometry

CHM 1045 : General Chemistry and Qualitative Analysis. Unit # 4: Aqueous Reactions and Solution Stoichiometry. Dr. Jorge L. Alonso Miami-Dade College – Kendall Campus Miami, FL. Textbook Reference : Module # 6 and 4 (V-VII) Chapt 4 (Brown & LeMay) Chapter # 3-6 to 3-8, 4 &

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Unit # 4: Aqueous Reactions and Solution Stoichiometry

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  1. CHM 1045: General Chemistry and Qualitative Analysis Unit # 4:Aqueous Reactions and Solution Stoichiometry Dr. Jorge L. Alonso Miami-Dade College – Kendall Campus Miami, FL • Textbook Reference: • Module # 6 and 4 (V-VII) • Chapt 4 (Brown & LeMay) • Chapter # 3-6 to 3-8, 4 & 11-1 to 11-3

  2. Solutions • Solutions (soln) are homogeneous mixtures of two or more pure substances. • The solvent (solv) is present in greatest abundance. • All other substances are solutes (solu). Volumetric flask Most useful measure of concentration of solutions: Moles of solute Molarity (M) = Liters of solution H2O Cu(NO3)2 {PrepASolu}

  3. Solubility of Chemical Substances Elements: mostlyinsolublesolids, liquids & gases. Covalent Compounds: mostlyinsolublegases, except O & N containing organic (C) liquids (polar: acids, bases, alcohols, etc.) Except PBS Except HAP Ionic Compounds: • Ionic Compounds: many are soluble. • SOLUBILITY RULES: for Ionic Compounds (Salts) • All salts of alkali metals (IA) are soluble. • All NH4+ salts are soluble. • All salts containing the anions: NO3-, ClO3-, ClO4-, (C2H3O2-) are soluble. • All Cl-, Br-, and I- are solubleexcept forHg22+, Ag+, and Pb2+ salts. • All SO42- are solubleexcept forPb2+, Ba2+, and Sr2+. • All O2- are insolubleexcept forIA metalsCa2+, Ba2+, and Sr2+ salts. • {Soluble metal oxides form hydroxides: CaO Ca 2+ + 2OH-} • 7. All OH- are insolubleexcept for IA metals, NH4+ & slightly soluble Ca 2+Ba2+ & Sr2+ • 8. All salts containing the anions: CO32-, PO43-, AsO43-, S2- and SO32- are insolubleexcept fro IA metals and NH4+ salts. • 9. For salts containing the anions not mentionedabove (e.g., CrO42-, Cr2O72-, P3-, C2O42- etc.) assume that they areinsolubleexcept for IA metals and NH4+ salts, unless, otherwise informed. H2O

  4. The Solution Process: Ionic vs. Molecular (1) Ionic Compounds: undergo dissociation - process by which many ionic substances dissolve in water, the solvent pulls the individual ions from the crystal and solvates them. _ {*NaCl + H2O } Polar water molecule + + H2O Dissociation NaCl(s) Electrolytes vs Nonelectrolytes? H2O Na+(aq) +Cl-(aq)

  5. Do soluble substances conduct electricity in water? • Electrolytes substances that dissociate in water and conduct electricity (many ionic salts) {ElectrVsNonE} H2O NaCl(s) Na+(aq) +Cl-(aq) H2O H2O(l) H+(aq) +OH-(aq) {DoesWaterConduct?} Anonelectrolytes may dissolve in water, but they do not dissociate into ions, thus do not conduct electricity. These are most commonly polarmolecular (covalent) compounds. C6H12O6(s) C6H12O6(aq) H2O Dissolved Glucose molecules Glucose molecules

  6. Electrolytes: Strong and Weak {Strong&WeakElectrolytes} • A strong electrolytedissociates completely when dissolved in water. HCl (g)H2O H+(aq) + Cl-(aq) • A weak electrolyteonly dissociates partially when dissolved in water. NH4OH(aq)H2O NH4+(aq) + OH-(aq) Aceitic Acid, HC2H3O2 (aq) H2O H+(aq)+ C2H3O2-(aq) 0  1  1  1 .75  1 .25  .25  .20  .80  1 .20  molecules ions

  7. Strong Electrolytes & Ion Concentration H2O NaCl (s) CaCl2 (s) Na3PO4 (s) Na+ + Cl- Ca2+ + 2Cl- 3Na++PO43- 1 1 1 (=2) H2O 1 1 2 (=3) H2O (=4) 1 3 1 1M Na3PO4 4M in Ions What Molarity of Ions?

  8. The Solution Process: Ionic vs. Molecular (2) Molecular (covalent) Compounds: mostlyinsolublegases, exceptpolar organic (C) liquids containing O & N (polar: acids, bases, alcohols, etc.) Insoluble gases: NO2, CH4, CO2, O2, P2O5, N2, CO, etc. Polar Covalent {carbon (C) chains containing H,O or N}: CH3OH, C6H12O6, C6H5OH, etc. H2O C6H12O6(s) C6H12O6(aq) H2O C3H5OH(l) C3H5OH (aq) Dissolve without dissociating into ions {Ethanol+Water}

  9. Molecular Compounds Molecular compounds tend to be nonelectrolytes, except for strong acids (and weak acids & bases). Covalent Compounds: HCl, CO2, O2, P2O5, C6H14, C6H12O6, etc. • Solubility Rules: • All salts containing the anions: NO3-, ClO3-, ClO4-, (C2H3O2-) are soluble. • All Cl-, Br-, and I- are solubleexcept forHg22+, Ag+, and Pb2+ salts. • All SO42- are solubleexcept forPb2+, Ba2+, and Sr2+. Strong Electrolytes: HCl. Weak Electrolytes: HF, Ammonia NH3, Acetic acid HC2H3O2 Non-Electrolyte: H2O, Ethanol C2H5OH 100% ions Some ions Dissolve, but no ions

  10. Chemical Reactions Occurring in Aqueous Environments (1) Precipitation (2) Gas-Forming (3) Acid-Base Neutralization (4) Oxidation-Reduction (Redox) Mostly Single & Double–Replacement Reactions

  11. (1) Precipitation Reactions A special category of Metathesis (Double Replacement, Exchange) Reactions

  12. Precipitation Reactions Aqueous solutions, reacting to produce a precipitate (an insoluble compound). Example: KI(aq) + Pb(NO3)2 (aq) Predict the solubility of compounds in reaction: Pb(NO3)2 + 2KI  2 KNO3 + PbI2 (aq) (aq) (aq) (s) Precipitate (ppt) Pb(NO3)2 • Solubility Rules: • All salts containing the anions: NO3-, ClO3-, ClO4-, (C2H3O2-) are soluble. • All Cl-, Br-, and I- are solubleexcept forHg22+, Ag+, and Pb2+ salts. • All SO42- are solubleexcept forPb2+, Ba2+, and Sr2+. KI PbI2 {Movie}

  13. It appears the ions in the reactant compounds exchange ion AgNO3 + KCl Precipitation Reactions are Double Displacement (Replacement) Does a reaction occur? Does the activity series apply to double displacement reactions? AgCl + KNO3 (aq) (aq) (s) (aq) • Reaction occurs only if a precipitate is formed! {*AgNO3+NaCl&NaI} • Solubility Rules: • All salts containing the anions: NO3-, ClO3-, ClO4-, (C2H3O2-) are soluble. • All Cl-, Br-, and I- are solubleexcept forHg22+, Ag+, and Pb2+ salts. • All SO42- are solubleexcept forPb2+, Ba2+, and Sr2+.

  14. Ways of Expressing Precipitation Reactions There are three different: • Molecular Equations (2) Ionic Equations (3) Net Ionic Equations AgNO3 (aq) + KCl(aq) AgCl(s) + KNO3 (aq) Ag+(aq) + NO3- (aq) + K+ (aq) + Cl-(aq)  AgCl(s) + K+(aq) + NO3- (aq) Ag+(aq) + Cl-(aq) AgCl(s)

  15. The molecular equation lists the reactants and products in their molecular (formula unit) form. AgNO3 (aq) + KCl(aq) AgCl(s) + KNO3 (aq) Molecular Equation Ionic Equation • In the ionic equation all strong electrolytes (strong acids, strong bases, and soluble ionic salts) are dissociated into their ions. • This more accurately reflects the species that are found in the reaction mixture. Ag+(aq) + NO3- (aq) + K+ (aq) + Cl- (aq)  AgCl(s) + K+(aq) + NO3- (aq)

  16. To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right. Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) AgCl(s) + K+(aq) + NO3-(aq) Net Ionic Equation • The only things left in the equation are those things that change (i.e., react) during the course of the reaction. Ag+(aq) + Cl-(aq) AgCl(s) • Those things that didn’t change (and were deleted from the net ionic equation) are called spectator ions.

  17. Solution Chemistry There are three different ways of expressing precipitation reactions: • Molecular Equations • Ionic Equations • Net Ionic Equations AgNO3 (aq) + KCl(aq) AgCl(s) + KNO3 (aq) Ag+(aq) + NO3- (aq) + K+ (aq) + Cl- (aq)  AgCl(s) + K+(aq) + NO3- (aq) Ag+(aq) + Cl-(aq) AgCl(s)

  18. Writing Net Ionic Equations • Write a balanced molecular equation. • Dissociate all strong electrolytes (ionic equation). • Cancel-out ions that remains unchanged from the left side to the right side of the equation (spectator ions). • Write the net ionic equation with the species that remain.

  19. Writing Net Ionic Equations 2NH4+ + SO42- + Ba2+ + 2NO3-  2NH4+ + 2NO3- + BaSO4 (aq) (aq) (aq) (aq) (aq) (aq) (s) Ba2+ + SO42-  BaSO4 (aq) (aq) (s) • Solubility Rules: • All salts containing the anions: NO3-, ClO3-, ClO4-, (C2H3O2-) are soluble. • All Cl-, Br-, and I- are solubleexcept forHg22+, Ag+, and Pb2+ salts. • All SO42- are solubleexcept forPb2+, Ba2+, and Sr2+.

  20. Precipitation Reactions • SOLUBILITY RULES: for Ionic Compounds (Salts) • All salts of alkali metals (IA) are soluble. • All NH4+ salts are soluble. • All salts containing the anions: NO3-, ClO3-, ClO4-, (C2H3O2-) are soluble. • All Cl-, Br-, and I- are solubleexcept forHg22+, Ag+, and Pb2+ salts. • All SO42- are solubleexcept forPb2+, Ba2+, and Sr2+. • SOLUBILITY RULES: for Ionic Compounds (Salts) • All salts of alkali metals (IA) are soluble. • All NH4+ salts are soluble. • All salts containing the anions: NO3-, ClO3-, ClO4-, (C2H3O2-) are soluble. • All Cl-, Br-, and I- are solubleexcept forHg22+, Ag+, and Pb2+ salts. • All SO42- are solubleexcept forPb2+, Ba2+, and Sr2+.

  21. SOLUBILITY RULES: for Ionic Compounds (Salts) • All salts of alkali metals (IA) are soluble. • All NH4+ salts are soluble. • All salts containing the anions: NO3-, ClO3-, ClO4-, (C2H3O2-) are soluble. • All Cl-, Br-, and I- are solubleexcept forHg22+, Ag+, and Pb2+ salts. • All SO42- are solubleexcept forPb2+, Ba2+, and Sr2+. • SOLUBILITY RULES: for Ionic Compounds (Salts) • All salts of alkali metals (IA) are soluble. • All NH4+ salts are soluble. • All salts containing the anions: NO3-, ClO3-, ClO4-, (C2H3O2-) are soluble. • All Cl-, Br-, and I- are solubleexcept forHg22+, Ag+, and Pb2+ salts. • All SO42- are solubleexcept forPb2+, Ba2+, and Sr2+.

  22. (2) Gas-Forming Reactions A special category of Metathesis (Double Replacement, Exchange) Reactions

  23. The expected products decompose to give a gaseous products Carbonate + Acid produce H2CO3CO2 + H2O Sulfites + Acids produce H2SO3 SO2+ H2O. CaCO3(s) + 2HCl (aq)  NaHCO3(aq) + HBr (aq)  SrSO3(s) + 2 HI(aq)  Gas-Forming Reactions These metathesis reactions do not give the expected products. CaCl2 (aq) + CO2(g) + H2O(l) NaBr (aq)+ CO2(g) + H2O(l) SrI2 (aq) + SO2(g) + H2O(l) • H2CO3 • H2CO3 • H2SO3 {CaCO3 + HCl*}

  24. Gas-Forming Reactions Aspirin C6H4(OCOCH3)COOH Alka Seltzer: aspirin + baking soda C9H8O4 NaHCO3 Aspirin: 2-(acetyloxy)benzoic acid or acetyl-salicylic acid H CH3 • C6H4(OCOCH3)COOH + NaHCO3 • C6H4(OCOCH3)COONa(aq) + {H2CO3(aq) } H2O • 2) { H2CO3(aq) } CO2 + H2O {Alka Seltzer Movie}

  25. Gas-forming Reactions 1. 2. 3. 4. 5.

  26. 2003 A

  27. (3) Acid-Base Neutralization Reactions Another special category of Metathesis (Double Replacement, Exchange) Reactions

  28. Acids • Arrhenius: Substances that release their H+ when dissolved in water. • Examples: Strong: HCl(g) H+(aq) + Cl-(aq) 100% molecule ions Weak: HC2H3O2 (aq). H+ + C2H3O2- (aq) 15% molecule ions

  29. Acids There are only seven strong acids: • Hydrochloric (HCl) • Hydrobromic (HBr) • Hydroiodic (HI) • Nitric (HNO3) • Sulfuric (H2SO4) • Chloric (HClO3) • Perchloric (HClO4) • Solubility Rules: • All salts containing the anions: NO3-, ClO3-, ClO4-, (C2H3O2-) are soluble. • All Cl-, Br-, and I- are solubleexcept forHg22+, Ag+, and Pb2+ salts. • All SO42- are solubleexcept forPb2+, Ba2+, and Sr2+.

  30. Bases • Arrhenius: Substances that release their OH− when dissolved in water. Strong: Ba(OH)2 (s) Ba2+(aq) + 2OH-(aq) 100% Weak: Mg(OH)2 (s) Mg2+(aq) + 2OH-(aq) 5% {IntroBases}

  31. Bases The strong bases are : • Alkali metals (IA) Hydroxides • BariumHydroxide • StrontiumHydroxide • (weaker: Ammonium, CalciumHydroxides) • SOLUBILITY RULES: for Ionic Compounds (Salts) • All OH- are insoluble except for IA metals, NH4+, Ba2+, and Sr2+.

  32. Generally, when solutions of an acid and a base are combined, the products are a salt and water. HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l) Neutralization Reactions (Arrhenius). H+ (aq)+ Cl- (aq)+ Na+ (aq) + OH-(aq) Na+ (aq)+ Cl- (aq)+ H2O (l) H+(aq) + OH- (aq) H2O (l)

  33. Neutralization Reactions Observe the reaction between a weak base, Milk of Magnesia, Mg(OH)2 (s)and a strong acid HCl (aq). How would you write the net ionic equation for such a reaction? {Movie} Mg(OH)2(s) + 2HCl (aq) MgCl2(aq) + 2H2O (l) Mg(OH)2(s) + 2H+(aq) + 2Cl-(aq)  Mg2+(aq) + 2Cl-(aq) + 2H2O (l) Mg(OH)2(s) + 2H+(aq) Mg2+(aq) + 2H2O (l)

  34. Acid-Base Neutralization Rxs

  35. Solution Stoichiometry Quantitative aspects of chemical reactions occurring in aqueous environments.

  36. moles of solute Molarity (M) = volume of solution in liters Preparing Solutions: Molarity • Most useful way to measure the concentration of a solution. Example 1: How would you prepare a 1M solution of CuSO4. 5H2O (FW= 249.7 g/mol) in a 250 mL volumetric flask? {Prep1MSoln} Example 2: How would you prepare a 0.5M solution of CuSO4. 5H2O (FW= 249.7 g/mol) in a 50 mL volumetric flask?

  37. moles of solute () Molarity (M) = volume of solution in liters (L) Calculations using Molarity moles of solute ()= Molarity ( /L)x volume of solution (L) mol () = = M x V (mol/L) x L

  38. Calculations using Molarity Molarity (M) Problem: What is the molecular weigh (g-MM) of an acid of which it takes 18.25 g to make 250. mL of a 2.00M concentration? 18.25 g

  39. Preparing Solutions: Dilution Moles of chemical from Solution 1 M1 x V1 mol1 = mol2 Moles of chemical in Solution 2 (mol/L)1 x L1 = (mol/L)2 x L2 Solution 1 Concentrated M2 x V2 Solution 2 Diluted M1 x V1 = M2 x V2

  40. Preparing Solutions by Dilution M1 x V1 = M2 x V2 How would you prepare 500 mL of a 1.0 M solution from a 2.0 M solution? M1 x V1 mol/L1 x L1 = mol/L2 x L2 mol1 = mol2 M2 x V2

  41. Preparing Solutions by Dilution M1 x V1 = M2 x V2 How would you prepare 500 mL of a 1.6 x 10-4 M solution from a 4.0 x 10-2 M solution? M1 x V1 mol/L1 x L1 = mol/L2 x L2 mol1 = mol2 M2 x V2 {*SolnByDilution}

  42. 2003A #5

  43. 2005 B

  44. 2006 (A) From: 3.0M NaOH Prepare: 100 mL 1.0M NaOH 100 mL Vol Flask

  45. Determining the Concentration of Solutions by Titration A volumetric analytical technique in which one can determine the concentration of a solute in a solution, by making it react with another solution of known concentration (standard). HCl (aq)+NaOH (aq)NaCl (aq) + H2O (l) Neutralization: # moles(acid)=# moles(base) (MxV)acid= (MxV)base Solution of unknown concentration (MA?) Solution of known concentration (MB) (Standard) React a known volume (VA) Measure reacting volume (VB)

  46. Titrations moles base () = MBVB moles acid () = moles base () HCl (aq)+NaOH (aq) NaCl (aq) + H2O (l) Does the acid need to be in solution? Can you titrate a solid acid to determine number of moles of acid? moles acid () = MAVA acid

  47. {*A-B w Ind} {A-B w/o Ind} Titration Phenolphthalein indicator ACID (clear) ↔ BASE (red) Neutralization: #moles1(acid) = #moles2(base)

  48. Titration: measuring the equivalence point Phenolphthalein in base Methyl orange in acid A pH meter or indicators are used to determine when the solution has reached the equivalence point, at which the stoichiometric amount of acid equals that of base.

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