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Acid-Base Titration and pH

Acid-Base Titration and pH. Chapter 16. Self-Ionization of water. Two water molecules produce a hydronium ion and a hydroxide ion by transfer of a proton. Pure water. Concentrations of hydronium and hydroxide ions of 1.0 x 10 -7 mol/L at 25 °C. Expressing concentrations.

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Acid-Base Titration and pH

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  1. Acid-Base Titration and pH Chapter 16

  2. Self-Ionization of water • Two water molecules produce a hydronium ion and a hydroxide ion by transfer of a proton chemistry chapter 16

  3. Pure water • Concentrations of hydronium and hydroxide ions of 1.0 x 10-7 mol/L at 25 °C. chemistry chapter 16

  4. Expressing concentrations • Brackets indicate concentration in mol/L • [H3O+] means • Hydronium ion concentration in moles per liter • or • Molar hydronium ion concentration chemistry chapter 16

  5. Ionization constant of water • 1.0 x 10-14 M2or (mol/L)2 • Constant over ordinary room temperatures • For pure water or dilute aqueous solutions chemistry chapter 16

  6. Solutions • Neutral • [H3O+]=[OH-] • Acidic • [H3O+]>[OH-] • Basic • [H3O+]<[OH-] chemistry chapter 16

  7. Strong bases • Ionize completely in solution • Molar concentration of hydroxide ions is the same as the molarity of the solution times the subscript of hydroxide. • Example: A 1.0 x 10-3 M LiOH solution has [OH-] of 1.0 x 10-3 M • Example: A 1.0 x 10-3 M Ca(OH)2 solution has [OH-] of 2.0 x 10-3 M chemistry chapter 16

  8. Strong Acids • Ionize completely in solution • Molar concentration of hydronium ions is the same as the molarity of the solution times the subscript of hydrogen. • Example: A 1.0 x 10-4 M HCl solution has [H3O+] of 1.0 x 10-4 M • Example: A 1.0 x 10-4 M H2SO4 solution has [H3O+] of 2.0 x 10-4 M chemistry chapter 16

  9. Using Kw • If you know the concentration of hydronium or hydroxide ions, you can use Kw to find the concentration of the other ion. • See page 484 chemistry chapter 16

  10. pH • The negative of the common logarithm of the hydronium ion concentration chemistry chapter 16

  11. pOH • The negative of the common logarithm of the hydroxide ion concentration chemistry chapter 16

  12. relationship chemistry chapter 16

  13. chemistry chapter 16

  14. Discuss • What is the concentration of hydronium and hydroxide ions in pure water at 25 °C? • For each of the following properties, is the solution acidic or basic? • [H3O+] = 1.0 x 10-3 M • [OH-] = 1.0 x 10-4 M • pH = 5.0 • pH = 8.0 chemistry chapter 16

  15. Acid-Base indicators • Used to obtain an approximate value for pH. • Compounds whose colors are sensitive to pH. • Weak acids or weak bases chemistry chapter 16

  16. Transition interval • The pH range over which an indicator changes color • See page 495 chemistry chapter 16

  17. Universal indicators • Use a combination of several different indicators. • pH paper has been soaked in a universal indicator. chemistry chapter 16

  18. pH meters • Used to find the exact pH • Measures the voltage between two electrodes placed in solution. • Changes with hydronium ion concentration chemistry chapter 16

  19. Titration • The controlled addition and measurement of the amount of a solution of known concentration required to react completely with a measured amount of a solution of unknown concentration. chemistry chapter 16

  20. Equivalence point • When the two solutions used in a titration are present in chemically equivalent amounts • Not always neutral chemistry chapter 16

  21. End point • The point in a titration at which an indicator changes color. • Can be used to find equivalence point. • If the indicator changes color at the equivalence point chemistry chapter 16

  22. Strong acid titrated with strong base chemistry chapter 16

  23. Weak acid titrated with strong base chemistry chapter 16

  24. Discuss • P. 503 section review 1 and 2. chemistry chapter 16

  25. Standard solution • The “known” solution • Its concentration is known precisely chemistry chapter 16

  26. Primary standard • Highly purified solid compound • Used to check the concentration of the known solution chemistry chapter 16

  27. Titration process • See pages 500 - 501 chemistry chapter 16

  28. Calculating the unknown concentration • Write the balanced chemical equation. • Determine the moles of the known solute. • Determine the moles of the unknown solute. • Determine the molarity of the unknown solution. chemistry chapter 16

  29. Example • A 25.00 mL sample of a solution of RbOH is neutralized by 19.22 mL of a 1.017 M solution of HBr. What is the molarity of the RbOH solution? • 0.7820 M chemistry chapter 16

  30. You try • If 29.96 mL of a solution of Ba(OH)2 requires 16.08 mL of a 2.303 M solution of HNO3 for complete titration, what is the molarity of the Ba(OH)2 solution? • 0.6182 M chemistry chapter 16

  31. You try • You have a 0.83 M vinegar solution. You are going to titrate 20.00 mL of it with a 0.519 M NaOH solution. At what volume of added NaOH solution would you expect to see an end point? • 37 mL chemistry chapter 16

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