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Models of Acids and Bases

Models of Acids and Bases. Arrhenius Concept : Acids produce H + in solution, bases produce OH  ion. Models of Acids and Bases (continued). Brønsted-Lowry : Acids are H + donors, bases are proton acceptors. HCl + H 2 O  Cl  + H 3 O + acid base.

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Models of Acids and Bases

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  1. Models of Acids and Bases • Arrhenius Concept: Acids produce H+ in solution, bases produce OH ion.

  2. Models of Acids and Bases (continued) • Brønsted-Lowry: Acids are H+ donors, bases are proton acceptors. • HCl + H2O  Cl + H3O+ • acid base

  3. Models of Acids and Bases (continued) • H3O+ • Hydronium ion • Also written as H+

  4. Conjugate Acid/Base Pairs • conjugate base: everything that remains of the acid molecule after a proton is lost. • conjugate acid: formed when the proton is transferred to the base.

  5. Conjugate Acid/Base Pairs (continued) • HA(aq) + H2O(l)  H3O+(aq) + A(aq) • acid1 base2 conj conj • acid 2 base 1

  6. Identify the conjugate base of: • HCN • HSO4- • HF • H2PO4-

  7. Identify the conjugate acid of: • NH3 • HCO3- • Br-

  8. Identify the products of the reactions and label conj. Acids & bases • HNO3 + H2O  • HSO4- + H2O  • NH3 + H2O  • NH4++ H2O  • HCO3- + OH- 

  9. Acid Dissociation Constant (Ka) • HA(aq) + H2O(l)  H3O+(aq) + A(aq) • pKa = -log(Ka)

  10. Acid Strength Strong Acid: • Its equilibrium position lies far to the right. (HNO3) • Ka ≈∞ • Yields a weak conjugate base. (NO3)

  11. Strong Acids HCl, HBr, HI, HNO3, H2SO4, HClO4, HClO3

  12. Acid Strength(continued) Weak Acid: • Its equilibrium lies far to the left. (CH3COOH) • Yields a much stronger (it is relatively strong) conjugate base than water. (CH3COO)

  13. Bases • “Strong” and “weak” are used in the same sense for bases as for acids.

  14. Base Dissociation Constant (Kb) • B(aq) + H2O(l)  BH+(aq) + OH(aq) • pKb = -log(Kb)

  15. Bases (continued) • strong = complete dissociation (hydroxide ion supplied to solution) • Kb ≈∞ • NaOH(s)  Na+(aq) + OH(aq)

  16. Strong Bases Group I metal hydroxides Ca(OH)2, Ba(OH)2, Sr(OH)2

  17. Bases(continued) • weak = very little dissociation (or reaction with water) • H3CNH2(aq) + H2O(l)  H3CNH3+(aq) + OH(aq)

  18. Polyprotic Acids • . . . can furnish more than one proton (H+) to the solution.

  19. Water as an Acid and a Base • Water is amphoteric (it can behave either as an acid or a base).

  20. Water as an Acid and a Base (continued) H2O + H2O  H3O+ + OH • acid 1 base2conj conj • acid 2 base 1 • Kw =[H3O+][OH] =1  1014 at 25°C

  21. The pH Scale • pH log[H+] • pH in water ranges from 0 to 14. • pH<7 acidic • pH>7  basic • pH = 7  neutral

  22. The pH Scale (continued) • pKw = 14.00 = pH + pOH • As pH rises, pOH falls (sum = 14.00).

  23. Equation Summary • pH = -log[H3O+] • pOH = -log[OH-] • pH + pOH = 14 • [H3O+][OH-] = Kw = 1x10-14 Ka x Kb = Kw pKa = -log(Ka) pKb = -log(Kb)

  24. Fill in the blanks

  25. What is the pH of a 0.15M solution of HCl?

  26. What is the pH of a o.32M solution of Ba(OH)2?

  27. The pH of a solution of Ba(OH)2 is 10.66 at 25°C. If the solution volume is 125mL, how many grams of Ba(OH)2 must have been dissolved?

  28. What is the pH of a 0.15M solution of acetic acid?

  29. What is the pH of a 0.21M solution of ammonia?

  30. pH of a mixture • What is the pH of a mixture of 1.3M nitric acid and 1.5M acetic acid?

  31. What is the pH of a mixture of 1.00M HCN and 5.00M HNO2? What is [CN-] at equilibrium?

  32. pH of polyprotic acids • What is the pH of 2.0M H2SO4? • Ka1=∞, Ka2=1.2x10-2 • 2nd H+ isn’t significant

  33. What is the pH of 0.0010M H2SO4?At lower concentrations the 2nd H+ may be significant

  34. Percent Dissociation (Ionization) For weak acids, % dissociation increases as the acid/base becomes more dilute.

  35. %dissociation calculations • Calculate the % dissociation of 1.00M acetic acid.

  36. 0.100M HC3H5O2 has 3.7% dissociation. What is the Ka value?

  37. Acid-base properties of salts • “Salt” – generic term for an ionic compound • Cation is a conjugate acid • Anion is a conjugate base • NaCl Na+ conjugate acid of NaOH Cl- conjugate base of HCl

  38. Acid-Base Properties of Salts

  39. Acidic, Basic, or neutral? • NaNO3 • NaNO2 • NH4NO2 • KOCL • C5H5NHClO4 • NH4OCl

  40. pH of salt solutions • What is the pH of a 1.0M solution of sodium acetate?

  41. What is the pH of a 0.5M solution of ammonium chloride?

  42. Structure and Acid-Base Properties • The weaker the H+ is bonded to the molecule, the stronger the acid • Two factors for acidity in binary compounds: • Bond Polarity(high is good) • Bond Strength(low is good)

  43. Choose the strongest acid • HIO3 or HBrO3 • HNO2 or HNO3 • HOCl or HOI • H3PO4 or H3PO3

  44. Oxides • Acidic Oxides • Nonmetal oxides produce acidic solutions in water • (Acid Anhydrides): • OX bond is strong and covalent. • SO2, NO2, CrO3

  45. Oxides (continued) • Basic Oxides • Metal oxides produce basic solutions in water • (Basic Anhydrides): • OX bond is ionic. • K2O, CaO

  46. Lewis Acids and Bases • Lewis Acid: electron pair acceptor • Lewis Base: electron pair donor

  47. Identify the Lewis acids and bases

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