Acids and Bases

1. Acids and Bases

2. Acids and Bases • Acid: a substance that, when dissolved in water, increases the concentration of H+ (protons) • HCl H+ + Cl- • HCl + H2O H3O+ + Cl- • Strong acid: an acid that completely ionizes/dissociates in water • HNO3 + H2O H3O+ + NO3- • Strong electrolyte H2O

5. Strong Acids: • Hydrochloric Acid HCl • Nitric Acid HNO3 • Sulfuric Acid H2SO4 • Perchloric Acid HClO4 • Hydrobromic Acid HBr • Hydroiodic Acid HI

7. Weak Acid: an acid that only partially ionizes/dissociates in water • CH3COOH(aq) CH3COO-(aq) + H3O+(aq) • Weak electrolytes • Weak Acids: • Phosphoric acid H3PO4 • Acetic Acid CH3COOH • Carbonic Acid H2CO3 • Hydrocyanic Acid HCN • Benzoic Acid C6H5COOH

9. Polyprotic Acids • Polyprotic acids: acids that can release more than one H+ • Sulfuric Acid • H2SO4(aq) HSO4-(aq) + H3O+(aq) • HSO4-(aq) SO42-(aq) + H3O+(aq)

10. Problem • Write out the equation(s) for the ionization of phosphoric acid, H3PO4, in water

11. Bases • Base: a substance that, when put in water, increases the concentration of OH- ions or a substance that accepts H+ ions • NaOH(aq)  Na+(aq) + OH-(aq) • Strong Bases: bases that completely ionize in water

14. Weak Bases: bases that only partially ionize in water • Ammonia: NH3 • Pyridine: C5H5N

17. Each acid has a conjugate base and every base has a conjugate acid Congugate Acid-Base Pairs conjugate acid-base pair 1 HA + B A− + BH+ conjugate acid-base pair 2

19. Problems Identify the conjugate bases for the following: • HBr • H2S • H2CO3 Identify the conjugate acids for the following • NO2- • NH3 • OH-

20. In the following equations, identify the conjugate acid and base pairs: • HCl + H2O  H3O+ + Cl- • C5H5N + H2O  C5H6N+ + OH-

22. Neutralization Reactions • When strong acids and bases in aqueous solution react with each other, they form water and a salt • HX(aq) + MOH(aq)  HOH(l) + MX(aq) • HCl(aq) + NaCl(aq)  H2O(l) + NaCl(aq) Water Salt

23. Problems Write out the molecular, total ionic, and net ionic equations for the reactions of the following acids and bases • HBr and KOH • HCl and Mg(OH)2 • H2SO3 and NaOH

26. Acid Ionization Constant • Acid Ionization Constant (Ka): the equilibrium constant for the ionization reaction of an acid with water • HA + H2O A- + H3O+ • Large Ka = Strong acid • Small Ka = Weak acid

28. Questions • Write the equilibrium constant expression for the dissociation of HCN (hydrocyanic acid) in water • Write the equilibrium expression for the dissociation of HF in water • If the Ka for HCN is 4.9 x 10-10 and the Ka for HF is 7.2 x 10-4, which acid is stronger?

29. Predict whether the equilibrium for each of the following reactions favors the reactants or products. • H3PO4(aq) + H2O(l) H3O+(aq) + H2PO4(aq) • NH4+(aq) + H2O(l) H3O+(aq) + NH3(aq)

30. Base Ionization Constant • Base Ionization Constant (Kb): the equilibrium constant for the ionization reaction of a base with water • B + H2O OH- + BH+ • Large Kb = Strong base • Small Kb = Weak base

32. Autoionization of Water

33. Autoionization of Water • Also called “Self Ionization” • About 1 out of every 10 million water molecules form ions through self ionization H2O Û H+ + OH– H2O + H2O Û H3O+ + OH– • All aqueous solutions contain both H3O+ and OH–

34. Ion Product Constant for Water • Ion Product Constant for Water (Kw): the numerical value obtained by multiplying the molar concentrations for hydronium and hydroxide ions present in pure water at 25°C • Kw = [H3O+][OH-] = 1.00 x 10-14 at 25 oC • the concentration of H3O+ and OH– are equal in pure water • [H3O+] = [OH–] = 10-7M @ 25°C

35. Ion Product of Water • the product of the H3O+ and OH– concentrations is always the same number • Kw =[H3O+][OH–] = 1.00 x 10-14 @ 25°C • if you measure one of the concentrations, you can calculate the other • as [H3O+] increases the [OH–] must decrease so the product stays constant • inversely proportional

36. H+ H+ H+ H+ H+ OH- OH- OH- OH- OH- [H+] vs. [OH-] Acid Base [H+] 100 10-1 10-3 10-5 10-7 10-9 10-11 10-13 10-14 [OH-]10-14 10-13 10-11 10-9 10-7 10-5 10-3 10-1 100 Even though it may look like it, neither H+ nor OH- will ever be 0

37. Acidic and Basic Solutions • Neutral solutions have equal [H3O+] and [OH–] • [H3O+] = [OH–] = 1 x 10-7 • acidic solutions have a larger [H3O+] than [OH–] • [H3O+] > [OH–] • [H3O+] > 1 x 10-7; [OH–] < 1 x 10-7 • basic solutions have a larger [OH–] than [H3O+] • [H3O+] < [OH–] • [H3O+] < 1 x 10-7; [OH–] > 1 x 10-7

38. Questions • Calculate the [OH] at 25°C when the [H3O+] = 1.5 x 10-9 M, and determine if the solution is acidic, basic, or neutral • Calculate the [H3O+] at 25°C in a solution that has a [OH] 1.3 x 10-10 M and determine if the solution is acidic, basic, or neutral • Calculate the [H3O+] at 25°C in a solution that has a [OH] 1.0 x 10-7 M and determine if the solution is acidic, basic, or neutral

39. pH and pOH • Acidic solutions • pH < 7 • Basic solutions • pH > 7 • Neutral solutions • pH = 7

41. pH is a measure of the concentration of H+ or H3O+ in solution • pH = -log [H+] OR pH = -log [H3O+] • [H3O+] = 10-pH • pOH is a measure of the concentration of OH- in solution • pOH = -log [OH-] • [OH-] = 10-pOH • pH + pOH = 14

42. Problems • What is the pH for an HCl solution with an [H3O+] = 2.3 x 10-2? • What is the pH of an NaOH solution with an [H3O+] = 3.39 x 10-10? • What is the pH of a KOH solution with a [OH-] = 1.1 x 10-2? • What is the [H3O+] for a solution with a pH of 8.45. What is the [OH-]?

43. Classification of Water Soluble Substances • Electrolytes: solutes that separate into ions when dissolved in water (they’re soluble) • Have the ability to conduct electricity • 2 types • Strong electrolytes • Weak electrolytes

44. Strong electrolytes: solutes that completely dissociates into ions when dissolved in water Examples: NaCl, MgBr2, HCl Strong electrical conductors Strong electrolyte(aq or s) → Cation+(aq) + Anion-(aq) Example: NaCl(s) → Na+(aq) + Cl-(aq)

45. Weak Electrolytes: solutes that, when dissolved in water, only partially dissociates into ions Examples: HF, NH3, acetic acid Weak electrical conductors Weak electrolyte(aq) ↔ Cation+(aq) + Anion-(aq) Example:HF(aq) ↔ H+(aq) + F-(aq)

46. Nonelectrolytes: solutes that dissolve in water without separating into ions • Examples: sucrose, ethanol • Do not conduct electricity • Nonelectrolyte (s or l) → Nonelectrolyte(aq) • Example: C12H22O11(s) → C12H22O11(aq)

47. Problems • The following salts are strong electrolytes. Write a balanced equation for their dissociation in water • LiBr • FeCl3 • HCN is a weak acid. Write a balanced equation for its dissociation in water • Do you expect Fructose (C6H12O6) to be a strong electrolyte, weak electrolyte, or nonelectrolyte? Write a balanced equation for its solvation in water

48. Titration • Titration: a procedure for the quantitative analysis of a substance of unknown concentration whereby a measured quantity of another substance, of know concentration, is completely reacted with the with the original substance. • Often used to determine the concentration of acids and bases

50. Equivalence point: the point in a titration at which one reactant has been exactly consumed by the by the addition of another reactant Midpoint of vertical rise Occurs at pH = 7 in a strong acid-strong base titration [H3O+] = [OH-]