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Acids & Bases Part 2

Acids & Bases Part 2. Strong Acids & Bases. The strength of an acid or a base is based on the percent of units dissociated. Weak Acids & Bases. Weak acids and bases only ionize partially

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Acids & Bases Part 2

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  1. Acids & Bases Part 2

  2. Strong Acids & Bases • The strength of an acid or a base is based on the percent of units dissociated

  3. Weak Acids & Bases • Weak acids and bases only ionize partially • A solution of weak acid contains a mixture of un-ionized acid molecules, hydronium ions, and the corresponding negative ions. • HCH3COO + H2O  CH3COO- + H3O+

  4. Strength Is Not Concentration • Although the terms weak and strong are used to compare the strengths of acids and bases, dilute and concentrated are terms used to describe the concentration of solutions. • Molarity is the most widely used unit for concentration • When we talk about strength (or degree of ionization) we will use Ka or Kb

  5. Calculating Solutions of Strong Acids and Bases • 0.10 M NaOH

  6. Calculating Solutions of Strong Acids and Bases • 7.5 x 10-4M Ca(OH)2

  7. Calculating Solutions of Strong Acids and Bases • Calculate the pH of a 1.0 M solution of HI

  8. Calculating Solutions of Strong Acids and Bases • Calculate the pH of a 0.050 M solution of HNO3.

  9. Calculating Solutions of Strong Acids and Bases • Calculate the pH of a 2.4 x 10-5 M solution of Mg(OH)2.

  10. pH of dissolved solids • Calculate the pH of a solution with 0.566 g of HI dissolved in 0.500 L of solution.

  11. pH of Diluted Solutions • Calculate the pH of a solution if 10.0 ml of 2.0 M HBr is diluted to 50.0 ml.

  12. 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]

  13. Acid & Base Ionization Constants • HCN + H2O  H3O+ + CN – • Write the Keq expression

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

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

  16. 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.

  17. Using pH to Calculate Ka • Calculate the Ka of a 0.220 M solution of H3ASO4 with a pH of 1.50.

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

  19. 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.

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