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Chapter 4: Aqueous Reactions

Chapter 4: Aqueous Reactions. homogeneous mixture of solute and solvent. Solution :. 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 homogeneous mixture of solute and solvent Solution: 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. Methanol dissolved in water Chapter 4: Aqueous Reactions Molecular Compounds Mostmolecular compounds do not dissociate in water + H2O methanol

  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 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) Strong electrolyte Strong electrolyte Strong electrolyte Non-electrolyte

  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 If the solution contains any type of ion, it is an electrolyte If all the dissolved particles are ions, the solution is a strong electrolyte HCOOH If only some of the dissolved particles are ions, the solution is a weak electrolyte HCOO- H+ Molecular Weak electrolyte

  8. Chapter 4: Aqueous Reactions Aqueous solutions that contain ions, conduct electricity Substance Ionic Molecular soluble highly soluble in H2O insoluble very little soluble in H2O Acid Base Neither acid nor base weak strong non-electrolyte weak electrolyte strong electrolyte strong electrolyte strong electrolyte strong bases are usually ionic compunds weak weak electrolyte

  9. Chapter 4: Aqueous Reactions Sample 1 Sample 2 Sample 3

  10. Chapter 4: Aqueous Reactions (1) (2) soluble in water insoluble in water (precipitate) (1) AgNO3 (aq) + NaCl (aq) → AgCl (s) + NaNO3 (aq) → PbI2 (s) + 2 NaNO3 (aq) (2) Pb(NO3)2 (aq) + 2 NaI (aq)

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

  12. Chapter 4: Aqueous Reactions Exchange or 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

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

  14. 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 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? 2 OH- Ni2+ + => Ni(OH)2 Na+ + NO3- => NaNO3

  15. Chapter 4: Aqueous Reactions PrecipitationReactions Digest of solubility rules: Salts of the following ions are alwayssoluble: • Group IA metals • Li+, Na+, K+ ... • Nitrate • NO3- • Ammonium • NH4+ • Acetate • C2H3O2- • [CH3COO-, AcO-]

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

  17. Chapter 4: Aqueous Reactions Precipitation Reactions (NH4)2SO4 soluble (NH4+ salt) AgCl insoluble CuSO4 soluble soluble (NO3- salt) FeNO3 Cu(OH)2 insoluble CaCO3 insoluble LiCl soluble (Li+ salt) soluble (C2H3O2- [acetate] salt) Ca(C2H3O2)2

  18. spectator ions Chapter 4: Aqueous Reactions 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!

  19. 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)

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

  21. 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

  22. Chapter 4: Aqueous Reactions Properties of Acids and Bases Acids • produce CO2 when • reacting with carbonates

  23. 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)

  24. Chapter 4: Aqueous Reactions Which of the following is insoluble? a. (NH4)CO3 b. ZnS c. K2CO3 d. Zn(NO3)2

  25. Chapter 4: Aqueous Reactions Properties of Acids and Bases Strong Acids when dissolved, 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

  26. Chapter 4: Aqueous Reactions Properties of Acids and Bases Weak Acids when dissolved, do not dissociate completely in water = weak electrolytes for example: HF Hydrofluoric acid CH3COOH Acetic acid HCOOH Formic acid ...

  27. Chapter 4: Aqueous Reactions 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 ...

  28. Chapter 4: Aqueous Reactions Properties of Acids and Bases Weak Bases generate few ions when dissolved =weak electrolytes for example: NH3 Ammonia NH3 (aq) + H2O (l) → NH4+ (aq) + OH-(aq)

  29. Chapter 4: Aqueous Reactions Neutralization Reactions acid base WATER salt (ionic compound) 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 (ionic compound)

  30. When writing an ionic equation, which compounds are written in ionic form? a. All compounds in the equation b. Reactants only c. Compounds that generate ions d. Hydroxide ions and protons (aq) Chapter 4: Aqueous Reactions What is the net ionic reaction for the reaction between insoluble lead(II) hydroxide and nitric acid? base acid salt water Pb(OH)2 (s) + 2 HNO3 (aq) → Pb(NO3)2 (aq) + 2 H2O (l)

  31. Chapter 4: Aqueous Reactions What is the net ionic reaction for the reaction between insoluble lead(II) hydroxide and nitric acid? base acid salt water Pb(OH)2 (s) + 2 HNO3 (aq) → Pb(NO3)2 (aq) + 2 H2O (l) Pb(OH)2 (s) + 2 H+(aq) + 2 NO3- (aq) → Pb2+ (aq) + 2 NO3- (aq) + 2 H2O (l) Pb(OH)2 (s) + 2 H+(aq) → Pb2+ (aq) + 2 H2O (l)

  32. 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

  33. Chapter 4: Aqueous Reactions Someone is preparing to cook pasta by adding 5.0 g of table salt (NaCl, 49.5 g/mol) to 400 mL of boiling water. What is the molarity of the resulting NaCl solution? 5.0 g moles concentration (molarity = mol/L) MM Volume (I) convert g NaCl into mol NaCl: (II) calculate molarity:

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

  35. 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

  36. Chapter 4: Aqueous Reactions What are the proton and hydroxide concentrations in a solution that has a pH of 4.3 ? pH = -log [H+] -pH = log [H+] 10-pH = [H+] [H+] = 10-4.3 =5.0 x 10-5M [H+] x [OH-] = 10-14 [OH-] = 10-14 2 x 10-10 M = 10-14= [H+] 5.0 x 10-5

  37. 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 =

  38. 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? Dilution: adding solvent without changing number of moles higher concentration lower concentration Vconc = 15mL = 0.015L Mconc= 0.65M Vdil = 0.3L + 15mL = 0.3L + 0.015L = 0.315L

  39. 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 (l) + 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

  40. 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)

  41. Na+ SO42- Na+ + Chapter 4: Aqueous Reactions What is the molarity of Na+ ions in a 0.2 M solution of Na2SO4 ? molarity Na+ ions molarity Na2SO4 empirical formula Na2SO4 (aq) → 2 Na+(aq) + SO42-(aq) Na+ SO42- Na+ = 0.4 M Na+

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