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Chapter 15 - Acids and Bases

Chapter 15 - Acids and Bases. Plus titration reactions from chapter 3. Arrhenius Definitions. Acid - Proton donor HA  H + + A - HCl  H + + Cl - Base - Hydroxide donor MOH  M + + OH - KOH  K + + OH -. Brønsted Lowry. Acid - Proton donor

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Chapter 15 - Acids and Bases

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  1. Chapter 15 - Acids and Bases Plus titration reactions from chapter 3

  2. Arrhenius Definitions • Acid - Proton donor HA  H+ + A- • HCl  H+ + Cl- • Base - Hydroxide donor MOHM+ + OH- • KOHK+ + OH-

  3. Brønsted Lowry • Acid - Proton donor HA + H2O  H3O+ + A- • HCl + H2O  H3O+ + Cl- • Base - Proton acceptor B: + H2O  BH+ + OH- • NH3 + H2O  NH4+ + OH-

  4. HA + B <==> BH+ + A- acid base acid base Conjugate acid/ base pairs differ by 1 proton.

  5. Protons in water • We write HA <=> H+ + A- • but H+ is never found by itself -- in aqueous solutions it joins with H2O to form H3O+ • So when we write [H+] we really mean [H3O+].

  6. Acid Strength • Strong acid  weak conjugate base • Weak acid  strong conjugate base • Strong base  weak conjugate acid • Weak base  strong conjugate acid • Makes sense -- if an acid gives up a proton easily, then its conjugate base is probably not very good at grabbing protons.

  7. Dissociation of Water • 2 H2O <==> H3O+ + OH- • K = [H3O+][OH-]/ [H2O]2 • the concentration of water is ~ 55M and can be treated as a constant. • so Kw = K[H2O]2 = [H3O+][OH-] = 1.0 x 10-14 M2

  8. Definition of pH • pH = -log [H+] = -log [H3O+] • so if [H3O+] = 2.48 x 10-4 then pH = -log 2.48 x 10-4 = 3.606

  9. [H3O+] = 10-pH • so if pH = 9.431 then [H3O+] = 10-9.431 = 3.707 x 10-10 M

  10. Calculating pH and pOH for strong acids and bases • For strong acids and bases • [H+] = [acid]  acidic protons/ molecule • [OH-] = [base]  hydroxides/ molecule

  11. The strong acids and bases are • Strong acids Strong bases • HClO4 NaOH • HCl KOH • HBr soluble hydroxides • HI • H2SO4 • HNO3

  12. Remember • pH = -log [H3O+] • pOH = -log [OH-] • [H3O+] [OH-] = 1.0 x 10-14 • pH + pOH = 14

  13. What are the values of [H3O+], [OH-], pH, and pOH for a 4.287 x 10-4 M solution of Ca(OH)2?

  14. [OH-] = 2(4.287 x 10-4 M) = 8.574 x 10-4 M • pOH = -log [OH-] = -log 8.574 x 10-4 = 3.0668 • pH = 14 - pOH = 14 - 3.067 = 10.9332 • [H3O+] = 10-10.9332 = 1.166 x 10-11 M

  15. If 350.0 mL of 0.1283 M sulfuric acid is mixed with 250.0 mL of 0.2899 M sodium hydroxide, what will be the pH of the solution?

  16. A noncarbonated soft drink contains an unknown amount of citric acid, H3C6H5O7. If 100.0 mL of the soft drink requires 33.51 mL of 0.01024 M NaOH to neutralize the citric acid completely, what is the concentration of citric acid in the soft drink in moles/liter (M)? In equivalents/liter (N)?

  17. Suppose you are given a 4.554 g sample that is a mixture of oxalic acid, H2C2O4, and another solid that does not react with sodium hydroxide. If 29.58 mL of 0.550 M NaOH is required to titrate the oxalic acid in the 4.554 g sample, what is the weight percent of oxalic acid in the mixture?

  18. A vitamin C tablet was analyzed to determine whether it did in fact contain, as the manufacturer claimed, 1.00 g of the vitamin. A tablet was dissolved in water to form a 100.00 mL solution, and a 10.00 mL sample was titrated with iodine (as KI3, potassium triiodide). It required 10.10 mL of 0.0521 M I3-1 to reach the stoichiometric point in the titration. Given that vitamin C, C6H8O6, is oxidized todehydroascorbic acid, C6H6O6 and triiodide, I3-1, is oxidized to iodide, I-1, write a balanced equation for the reaction and determine whether the manufacturer’s claim is correct? (MW vitamin C = 176 g/mol)

  19. A 35.49 mL sample of 0.2430 M H2SO4 is mixed with 65.33 mL of a 0.4199 M sample of KOH. Determine the concentration of all ions in solution, the pH, and pOH.

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