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Acids & Bases

Acids & Bases. Part 2. Acid & Base Ionization Constants. A weak acid or base produces a reaction that only partially goes forward. The acid or base ionization constant measures the degree of ionization (or the strength) The smaller the Ka, the weaker the acid

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Acids & Bases

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  1. Acids & Bases Part 2

  2. Acid & Base Ionization Constants • A weak acid or base produces a reaction that only partially goes forward. • The acid or base ionization constant measures the degree of ionization (or the strength) • The smaller the Ka, the weaker the acid • The smaller the Kb, the weaker the base • Keq = [products] [reactants] • 1 x 10 -14 = Ka x Kb

  3. Acid & Base Ionization Constants • Write the Ka expressions for the following reactions: • HClO2 + H2O  H3O+ + ClO2- • HIO + H2O  H3O+ + lO-

  4. Acid & Base Ionization Constants • Write the Kb expression for CH3NH2

  5. Common Ka Values(You may need this for some of the homework problems!)

  6. Using pH to Calculate Ka • Suppose you measure the pH of a 0.100 M solution of HCOOH (formic acid) and found it to be 2.38. Calculate the Ka.

  7. Using pH to Calculate Ka HCOOH + H2O  COOH- + H3O+

  8. Using pH to Calculate Ka • Calculate the Ka of a 0.220 M solution of H3AsO4 with a pH of 1.50. Calculate the pKa

  9. % Ionization • A 0.10 M solution of a weak acid (HX) is 17.5% ionized. Calculate Ka.

  10. % Ionization • HX + H20  X- + H30+

  11. Another Example • A sample of a weak acid HX has a pH of 3.5. If the Ka = 2.7 x 10 -5, calculate the initial concentration of HX.

  12. Another Example • HX + H20  X- + H30+

  13. More Examples • What is the pH of a 25 ml sample of 0.25 M HC2H3O2? Ka = 1.8 x 10 -5 • pH = 2.676

  14. Example • What is the % dissociation of a 0.325 M solution of HCOOH? Ka = 1.8 x 10 -4

  15. Weak Mixtures • Calculate the pH of a solution that contains 1.00 M HCN & 5.00 M HNO2. Also calculate the [CN-] at equilibrium. KaHCN = 6.2 x 10 -10 & KaHNO2 = 4.0 x 10 -4

  16. HNO2 H+ + NO2- Weak Mixtures

  17. Part 2 of question… Also calculate the [CN-] at equilibrium. HCN  H+ + CN- Weak Mixtures

  18. Another example • What is the pH when 25 ml of 0.25 M HNO3 is mixed with 25 ml of 0.25 M HNO2 (Ka HNO2 = 4.0 x 10-4)

  19. Example • What is the pH of a 0.25 M solution of NH3. KbNH3 = 1.8 x 10-5

  20. One more example • What is the pH of a mixture of 25 ml of a 0.25M KOH solution & 25 ml of 0.25 M CH3NH2?

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