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Chapter 4: Aqueous Reactions

Chapter 4: Aqueous Reactions. Solution : homogeneous mixture of solute and solvent. Solvent: substance present in the larger amount Solute: substance(s) dissolved in solvent, generally present in lesser amounts than solvent. -. -. +. -. +. + H 2 O. -. +. +. +. -. -. +. -.

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Chapter 4: Aqueous Reactions

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  1. Chapter 4: Aqueous Reactions Solution: homogeneous mixture of solute and solvent Solvent: substance present in the larger amount Solute: substance(s) dissolved in solvent, generally present in lesser amounts than solvent

  2. - - + - + + H2O - + + + - - + - Chapter 4: Aqueous Reactions Ionic Compounds When ionic compounds dissolve in water, they dissociate completely NaCl (aq) → Na+ (aq) + Cl-(aq)

  3. Chapter 4: Aqueous Reactions Molecular Compounds Most molecular compounds do not dissociate in water + H2O methanol Methanol dissolved in water

  4. Weak acids, such as acetic acid, dissociate only partially: CH3COOH (aq) H+ (aq) + CH3COO- (aq) Chapter 4: Aqueous Reactions Molecular Compounds Somemolecular compoundsdissociate (ionize)in water (acids) Strong acids, such as hydrochloric acid, dissociate completely: HCl (aq) → H+ (aq) + Cl- (aq)

  5. Chapter 4: Aqueous Reactions HW: 1,3,18,37 Aqueous solutions that contain ions, conduct electricity Electrolytes: substances that generate ions when dissolved in water strong electrolyte For example: • Ionic compounds strong electrolyte • Strong acids weak electrolyte • Weak acids strong electrolyte • Strong bases weak electrolyte • Weak bases Non-Electrolytes: substances that do not generate ions when dissolved in water

  6. Chapter 4: Aqueous Reactions Strong, Weak, and Non- Electrolytes AgI NaCl sugar HCl Ag+ Cl- Cl- C12H22O11 I- Na+ H+ Molecular Ionic Ionic Molecular (dissociated acid)

  7. Chapter 4: Aqueous Reactions Strong, Weak, and Non- Electrolytes Electrolytes and Non-Electrolyte definition only refers to the molecules/ions that are dissolved Formic acid HCOOH HCOO- H+ Molecular

  8. Chapter 4: Aqueous Reactions Some reactions involving ionic compounds: Exchange ot Metathesis Reactions + - + - + - + - AX + BY→ AY + BX

  9. Chapter 4: Aqueous Reactions Some reactions involving ionic compounds: Exchange ot Metathesis Reactions If one of the products in insoluble, the reaction is a precipitation reaction: AgNO3 (aq) + NaCl (aq) → AgCl (s) + NaNO3 (aq) white precipitate AgI (s) + NaNO3 (aq) AgNO3 (aq) + NaI (aq) → brownish precipitate

  10. Chapter 4: Aqueous Reactions PrecipitationReactions AgI (s) + NaNO3 (aq) AgNO3 (aq) + NaI (aq) → brownish precipitate heterogeneous mixture!

  11. 2 (aq) (aq) (s) (aq) A: X: A: Y: Ni2+ OH- II) Exchange X and Y: Na+ NO3- B: X: B: Y: Chapter 4: Aqueous Reactions HW: 15 PrecipitationReactions 2 Ni(NO3)2 + NaOH → Ni(OH)2 + NaNO3 Ni2+ NO3- I) Identify ions: Na+ OH- III) Determine stoichiometry of compounds formed: IV) Balance equation! V) Is there an insoluble product? Ni2+ + OH- => Ni(OH)2 Na+ + NO3- => NaNO3

  12. Chapter 4: Aqueous Reactions PrecipitationReactions How do you know which ionic compounds are soluble?

  13. Chapter 4: Aqueous Reactions HW: 10,19,22 PrecipitationReactions Digest of solubility rules: Salts of the following ions are alwayssoluble: • Group IA metals • Li+, Na+, K+ ... • Nitrate • NO3- • Ammonium • NH4+ • Acetate • C2H3O2-

  14. Chapter 4: Aqueous Reactions HW: 90 Precipitation Reactions (NH4)2SO4 AgCl CuSO4 FeNO3 Cu(OH)2 CaCO3 LiCl Ca(C2H3O2)2

  15. spectator ions Chapter 4: Aqueous Reactions HW: 23 Net Ionic Equations Molecular Equation (shows undissociated compounds): Ni(NO3)2(aq) + 2 NaOH (aq) → Ni(OH)2(s) + 2 NaNO3(aq) Ionic Equation: Ni2+(aq) + 2 NO3-(aq) + 2 Na+(aq) + 2 OH-(aq)→ Ni(OH)2(s) + 2 Na+(aq) + 2 NO3-(aq) Net Ionic Equation: Ni2+(aq) + 2 OH-(aq)→ Ni(OH)2(s) The spectator ions do not participate in the reaction!

  16. Chapter 4: Aqueous Reactions CaCO3 (s) Ca(NO3)2 (aq) + Na2CO3 (aq) → (aq) 2 + NaNO3 Spectator ions: 2 Na+, 2 NO3- Net ionic equation: Ca2+ (aq) + CO32- (aq) → CaCO3 (s)

  17. Chapter 4: Aqueous Reactions Ca(C2H3O2)2 Ca(NO3)2 (aq) + NaC2H3O2 (aq) → 2 2 + NaNO3 Spectator ions: ALL ! If all salts are soluble, no precipitation reaction will take place

  18. Chapter 4: Aqueous Reactions Properties of Acids and Bases Acids Bases • taste sour • taste bitter • turn blue litmus red • turn red litmus blue • produce CO2 when • reacting with carbonates • produce H2 when • reacting with metals • generate protons, H+, when • dissolved in water • generate hydroxide ions, OH-, • when dissolved in water

  19. Chapter 4: Aqueous Reactions Properties of Acids and Bases Strong Acids = dissociate completely in water = strong electrolytes HCl Hydrochloric acid HBr Hydrobromic acid HI Hydroiodic acid HNO3 Nitric acid H2SO4 Sulfuric acid HClO3 Chloric acid HClO4 Perchloric acid

  20. Chapter 4: Aqueous Reactions HW: 36 Properties of Acids and Bases Strong Bases strong electrolytes Metal Hydroxides of Group IA metals: NaOH, KOH ... Metal Hydroxides of Group IIA metals: Ca(OH)2 , Mg(OH)2 ...

  21. Chapter 4: Aqueous Reactions The reaction of acids with carbonate salts: MgCO3 (s)+ HCl (aq)→ MgCl2(aq) + H2CO3(aq) 2 unstable H2CO3 (aq) → CO2 (g) + H2O (l) Overall: 2 MgCO3 (s)+ HCl (aq)→ MgCl2(aq) + CO2(g) + H2O (l)

  22. Chapter 4: Aqueous Reactions HW: 39 Neutralization Reactions acid base WATER salt HNO3(aq)+ NaOH (aq) → H2O (l) + NaNO3 (aq) net ionic equation: H+(aq) + NO3-(aq)+ Na+ (aq) + OH- (aq) → H2O (l) + Na+ (aq) + NO3- (aq) H+(aq) + OH- (aq) → H2O (l) In a neutralization reaction, an acid and a base react to form water and a salt

  23. Chapter 4: Aqueous Reactions Complete and balance the following neutralization reaction: 2 Mg(OH)2 (aq)+ HBr (aq)→ MgBr2(aq) + H2O (l) 2 net ionic equation: Mg2+(aq) + 2 OH- (aq) + 2 H+(aq) + 2 Br- (aq) → Mg2+(aq) + 2 Br- (aq) + 2 H2O (l) net: 2OH- (aq) + 2H+(aq) → 2H2O (l) OH- (aq) + H+(aq) → H2O (l)

  24. Chapter 4: Aqueous Reactions Concentrations of Solutions ... are measured in Molarity Molarity The concentration of 0.4 L of solution containing 0.25 moles of sugar is = 0.6 M

  25. Chapter 4: Aqueous Reactions HW: 62,73 Someone is preparing to cook pasta by adding 5.0 g of table salt (NaCl, formula mass = 49.5 g/mol) to 400 mL of boiling water. What is the molarity of the resulting NaCl solution? (I) convert g NaCl into mol NaCl: (II) calculate molarity:

  26. Na+ SO42- Na+ + Chapter 4: Aqueous Reactions What is the molarity of Na+ ions in a 0.2 M solution of Na2SO4 ? Na2SO4 (aq) → 2 Na+ + SO42- Na+ SO42- Na+ Each formula unit of Na2SO4 that dissolves gives rise to 1 SO42- ion and 2 Na+ ions = 0.4 M Na+

  27. Chapter 4: Aqueous Reactions Proton Concentration in Aqueous Solutions [H+]≡ proton concentration pH = -log [H+] and [H+] = 10-pH [H+] = 0.001 M [H+] = 0.001 M = 1 x 10-3 M pH = -log(1 x 10-3) = 3 [H+] x [OH-] = 10-14 = constant Neutral solution: [H+] = [OH-] = 10-7 M The pH scale 1 2 3 4 5 6 78 9 10 12 13 14 acidic neutral basic

  28. Chapter 4: Aqueous Reactions What are the proton and hydroxide concentrations in a solution that has a pH of 4.3 ? pH = -log [H+] [H+] = 10-pH [H+] = 10-4.3 [H+] x [OH-] = 10-14 [OH-] = 10-14 = 10-14= [H+] 5.0 x 10-5

  29. Chapter 4: Aqueous Reactions How many moles of HF are needed to make 0.15 L of a 0.13M solution? (how many moles HF are in 0.15 L of a 0.13 M solution?) 1 L of a 0.13 M solution: 0.15 L of a 0.13 M solution: x0.15 L =0.02 mol HF

  30. add solvent Chapter 4: Aqueous Reactions Dilutions number of solute molecules before dilution number of solute molecules after dilution = number of moles of solute before dilution number of moles of solute after dilution =

  31. Chapter 4: Aqueous Reactions What is the concentration of a solution that is made by adding 0.3L of water to 15mL of a 0.65M solution? Vconc = 15mL = 0.015L Mconc= 0.65M Vdil = 0.3L + 15mL = 0.3L + 0.015L = 0.315L

  32. Chapter 4: Aqueous Reactions HW: 79a,d Solution Stoichiometry and Chemical Analysis What volume of a 0.30 M HCl solution is needed to completely react 3.5 g of Ca(OH)2 ? 2 HCl (aq) + Ca(OH)2 (aq) → 2 H2O (aq) + CaCl2 (aq) Strategy: moles Ca(OH)2 → moles HCl → Liters HCl 3.5 g Ca(OH)2→ molar mass = 74g/mol stoichiometric factor from equation molarity of solution

  33. Chapter 4: Aqueous Reactions Solution Stoichiometry and Chemical Analysis What volume of a 0.30 M HCl solution is needed to completely react 3.5 g of Ca(OH)2 ? 2 HCl (aq) + Ca(OH)2 (aq) → 2 H2O (aq) + CaCl2 (aq)

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