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Chapter 4 Aqueous Reactions and Solution Stoichiometry

Chapter 4 Aqueous Reactions and Solution Stoichiometry

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Chapter 4 Aqueous Reactions and Solution Stoichiometry

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  1. Chapter 4Aqueous Reactions and Solution Stoichiometry

  2. Chapter Objectives • Metathesis reactions (double replacement) • precipitation reactions • acid-base reactions • redox reactions • Single Replacement reactions (displacement) • activity series • Molar concentration • Solution Stoichiometry • titration • indicators

  3. General Properties of Aqueous Solutions • Homogeneous mixtures of two or more pure substances. • The solvent in greatest abundance. • All other substances are solutes. • If water is the solvent the solution is aqueous

  4. Electrolytic Properties • whether or not solutions conduct electricity. • If ions form in solution, the substance is an electrolyte and the solution conducts electricity. e.g. NaCl. • If no ions form, the substance is a nonelectrolyte. e.g. sucrose. • Ions form in solution through the process of dissociation.

  5. Dissociation • Solid does not exist as a well-ordered crystal. • Each ion surrounded by a shell of water molecules. • cations have oxygen end of water pointing in. • anions have hydrogen end of water pointing in. • Ions move to cause electric current to flow through solution. • Electrolytes - Soluble ionic compounds • Non-electrolytes - Molecular compounds

  6. Electrolytes • A strong electrolyte dissociates completely when dissolved in water. • ionic compounds, many acids & bases. • A weak electrolyte only dissociates partially when dissolved in water. • weak acids and bases.

  7. Solvation Equations • A substance dissolves in a solvationreaction: • sugar is a non-electrolyte: C12H22O11(s) → C12H22O11(aq) • soluble ionic compounds undergo dissociation in solution; break up into constituent ions: NaCl(s) → Na1+(aq) + Cl1-(aq) (this represents both solvationand dissociation)

  8. to write a dissociation equation for any ionic compound identify the cation and anion, then write the balanced equation: • Al2(SO4)3(s) contains Al3+ and SO42- ions. • When it dissociates you get 2 Al3+ and 3 SO42- ions: Al2(SO4)3(s) → 2 Al3+(aq) + 3 SO42-(aq) • (make sure the equation is balanced)

  9. Write dissociation equations for the ionic substances in questions 4.15 and 4.16

  10. Precipitation Reactions • When a mixture of soluble ions forms a compound that is insoluble, a precipitate is formed. • Pb(NO3)2 (aq) + 2 KI(aq)PbI2 (s) + 2 KNO3 (aq)

  11. Solubility Guidelines for Ionic Compounds • Solubility is the amount of a substance that can be dissolved in a given quantity of solvent at that temperature. • Measured in g/100g H2O, or mol/L • Solubility < 0.01 mol/L is insoluble. • Experimental observations have led to empiricalguidelines for predicting solubility.

  12. Solubility of Selected Ions (soluble > 0.1 mol/L)

  13. Predicting Solubility • Na2S • soluble, because Na is an alkali metal (group 1) • NH4Cl • soluble, because the NH41+ ion is soluble with any anion • CuNO3 • soluble, because NO31- is soluble with any cation • AgCH3COO • insoluble • Mg(CH3COO)2 • soluble • PbCl4 • soluble; in this compound the Pb is 4+ • PbCl2 • insoluble; in this compound the Pb is 2+

  14. Predicting Solubility • KCl • NaNO3 • AgCl • Al2(SO4)3 • FeS • Ca3(PO4)2 • BaSO4 • Pb(ClO3)2 • (NH4)2S • PbCl2

  15. Complete questions 4.19 and 4.20

  16. Metathesis (Exchange) Reactions Metathesis comes from a Greek word that means “to transpose” AgNO3 + KCl AgCl (s) + KNO3 (aq)

  17. Metathesis (Exchange) Reactions Metathesis comes from a Greek word that means “to transpose” It appears the ions in the reactant compounds exchange, or transpose, ions AgNO3 + KCl AgCl (s) + KNO3 (aq)

  18. Metathesis (Exchange) Reactions Metathesis comes from a Greek word that means “to transpose” It appears the ions in the reactant compounds exchange, or transpose, ions AgNO3 + KCl AgCl + KNO3

  19. Metathesis (Exchange) Reactions Metathesis comes from a Greek word that means “to transpose” It appears the ions in the reactant compounds exchange, or transpose, ions always indicate the phase of the substance, where known most are reactions of ionic compounds AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq)

  20. Chemical Equations of Metathesis Reactions

  21. Molecular Equation The molecular equation lists the reactants and products in their molecular form. AgNO3 (aq) + KCl(aq) AgCl(s) + KNO3 (aq)

  22. Complete Ionic Equation All strong electrolytes 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)

  23. Net Ionic Equation 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)

  24. Net Ionic Equation To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right. 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)

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

  26. Writing Net Ionic Equations • Write a balanced molecular equation. • Dissociate all strong electrolytes. Write the complete ionic equation. • Cross out anything that remains unchanged from the left side to the right side of the equation. • Write the net ionic equation with the species that remain.

  27. Write the balanced molecular equation, complete ionic equation and net ionic equation for the following: • FeCl2 (aq) + K2S (aq) • AlBr3 (aq) + NaOH(aq) • (NH4)3PO4 (aq) + Ca(NO3)2 (aq)  • Aqueous solutions of silver nitrate and sodium carbonate react. • Aqueous solutions of barium chloride and potassium sulfate react.

  28. Complete questions 4.22 and 4.24. In each reaction with a precipitate write the balanced molecular equation, complete ionic equation and net ionic equation • Hand in on:

  29. Acids: • 2 definitions: • Substances that increase the concentration of H1+ when dissolved in water (Arrhenius). • Proton donors (Brønsted–Lowry). • If an acid can donate more than one proton it is diprotic or triprotic.

  30. Acids Strong acids dissociate completely in water There are only seven strong acids: • Hydrochloric (HCl) • Hydrobromic (HBr) • Hydroiodic (HI) • Nitric (HNO3) • Sulfuric (H2SO4) • Chloric (HClO3) • Perchloric (HClO4)

  31. Bases: • Substances that increase the concentration of OH1- when dissolved in water (Arrhenius). • Proton acceptors (Brønsted–Lowry).

  32. Bases Strong bases dissociate completely in water. The strong bases are the soluble salts of hydroxide ion: • Alkali metals (LiOH, NaOH, etc) • Ca(OH)2, Sr(OH)2, Ba(OH)2

  33. Weak Acids and Bases • are weak electrolytes. • Therefore, they are partially ionized in solution. • HF(aq) is a weak acid; most acids are weak acids. • We write the ionization of HF as: • HF  H1+ + F1-

  34. Identifying Strong & Weak Electrolytes • Compounds can be classified as by looking at their solubility: • Strong electrolytes: • Ionic compounds. • Strong acids are strong electrolytes. • Weak electrolytes: • Weak acids and bases. • Nonelectrolytes: • All other compounds.

  35. Complete questions 4.35 to 4.38

  36. Acid-Base Reactions In an acid-base reaction, the acid donates a proton (H+) to the base.

  37. Neutralization Reactions When solutions of an acid and a base are combined, the products are a salt and water. Molecular Equation: HCl(aq) + NaOH(aq) NaCl(aq)+ H2O (l) acid base salt water a salt is any non-acidic or basic ionic compound

  38. Neutralization Reactions When a strong acid reacts with a strong base, the complete ionic equation is… HCl(aq)+ NaOH(aq)  NaCl(aq)+ H2O (l) H+ (aq)+ Cl- (aq)+ Na+ (aq) + OH-(aq)  Na+ (aq)+ Cl- (aq)+ H2O (l)

  39. Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is… HCl(aq)+ NaOH(aq)  NaCl(aq)+ H2O (l) H+ (aq)+ Cl- (aq)+ Na+ (aq) + OH-(aq)  Na+ (aq)+ Cl- (aq)+ H2O (l) H+ (aq)+ OH- (aq) H2O (l)

  40. Mg(OH)2 (s) + HCl(aq) • Molecular Equation: • Mg(OH)2 (s) + 2 HCl(aq) MgCl2 (aq) + 2 H2O (l) • Complete Ionic Equation: • Mg(OH)2 (s) + 2 H1+(aq) + 2 Cl1-(aq) Mg2+(aq) + 2 Cl1-(aq) + 2 H2O (l) • Net Ionic Equation: • Mg(OH)2 (s) + 2 H1+(aq)  Mg2+(aq) + 2 H2O (l)

  41. Complete questions 4.39 & 4.40

  42. Gas-Forming Reactions • Reaction of sulfides with acid gives rise to H2S(g). • FeS (s) + 2 HCl (aq)  FeCl2 (aq) + H2S (g) • Reaction of sulfites with acid gives rise to SO2 (g). • SrSO3 (s) + 2 HI (aq)  SrI2 (aq) + SO2 (g) + H2O (l)

  43. Gas Forming Reactions • Acid with carbonate or hydrogen carbonate forms CO2: • CaCO3 (s) + HCl(aq)  CaCl2 (aq) + CO2 (g) + H2O (l) • NaHCO3 (aq) + HBr(aq)  NaBr(aq) + CO2 (g) + H2O (l) • Bases with ammonium compounds gives ammonia gas: • NH4Cl(aq) + NaOH(aq)  NH3 (g)+ H2O(l) + NaCl(aq)

  44. Complete question 4.43

  45. Oxidation-Reduction Reactions • Involve the transfer of electrons • An oxidation occurs when an atom or ion loses electrons. (LEO) • A reduction occurs when an atom or ion gains electrons. (GER) • In all redox reactions, one species is reduced at the same time as another is oxidized.

  46. Oxidation Numbers • used to determine if an oxidation-reduction reaction has occurred • we assign a charge to each element in a neutral compound or charged entity. • these charges, real or virtual, are called oxidation numbers

  47. Rules of Oxidation Numbers • Elements have an oxidation number of 0. • The oxidation number of a monatomic ion is the same as its charge. • Oxygen has an oxidation number of 2- (except peroxides, O22-) • Hydrogen has an oxidation number of 1+ (except hydrides, H1-) • The sum of the oxidation numbers in a neutral compound is 0. • The sum of the oxidation numbers in a polyatomic ion is the charge on the ion.

  48. Calculation of Oxidation Numbers • H2O - H is 1+, O is 2- • H2O2 • H is 1+, O is 1- • AlH3 • Al is 3+, H is 1- • CaCl2 • Ca is 2+, Cl is 1- • PbS2 • Pb is 4+, S is 2- • Mn3N7 • Mn is 7+, N is 3- • H2SO4 • H is 1+, S is 6+, O is 2- • Cr2O72- • Cr is 6+, O is 2-

  49. complete questions 4.49 and 4.50

  50. Recognizing Oxidation and Reduction • Consider the following balanced chemical equation: • 3 Cu2+ + 2 Al  3 Cu + 2 Al3+ • Let’s apply what we know about oxidation numbers to this equation: • 3 Cu2+ + 2 Al  3 Cu + 2 Al3+ • O.N. 2+ 0 0 3+