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Titration

Titration. Titration. Strong acids ionize almost completely Weak acids don’t ionize very much [H 3 O +1 ] is not the same as the acid concentration. [H 3 O +1 ]. Can’t be measured directly Determined by comparison. Acid-Base Titration. Carefully controlled neutralization reaction

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Titration

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  1. Titration

  2. Titration • Strong acids ionize almost completely • Weak acids don’t ionize very much • [H3O+1] is not the same as the acid concentration

  3. [H3O+1] • Can’t be measured directly • Determined by comparison

  4. Acid-Base Titration • Carefully controlled neutralization reaction • Requires a standard solution and an acid-base indicator • Standard solution is: acid or base of known concentration

  5. Titration • Standard solution is slowly added to unknown solution • As solutions mix: • a neutralization reaction occurs • Eventually: • enough standard solution is added to neutralize the unknown solution Equivalence point

  6. Equivalence point Total number of moles of H+1 ions donated by acid = total number of moles of H+1 accepted by base • Total moles H+1 = total moles OH-1

  7. Titration • End-point = point at which indicator changes color • if indicator chosen correctly: • end-point very close to equivalence point

  8. 14- Between pH of 4 and 10, only a fewdropsof base are added Equivalence Pt    0 ml 20 ml Titration of a strong acid with a strong base Phenolphthalein Color change: 8.2 to 10  pH 7- 0-  Volume of 0.100 M NaOH added (ml) 40ml

  9. MH+1VH+1 = MOH-1VOH-1 • MH+1 = molarity of H+1 • MOH-1 = molarity of OH-1 • VH+1 = volume of H+1 • VOH-1 = volume of OH-1

  10. MaVa = MbVb • True for: monoprotic acids and monohydroxy bases

  11. Titration Problem #1 • In a titration of 40.0 mL of a nitric acid solution, the end point is reached when 35.0 mL of 0.100 M NaOH is added Calculate the concentration of the nitric acid solution

  12. Neutralization Reaction • HNO3 + NaOH  H2O + NaNO3 • HNO3 is a monoprotic acid

  13. Variables • Ma = ? • Va = 40.0 mL • Mb = 0.100 M • Vb = 35.0 mL

  14. Plug and Chug • X (40.0 mL) = (0.100 M )(35.0 mL) • X = .875 M = nitric acid

  15. Titration Problem #2 • What is the concentration of a hydrochloric acid solutionif50.0 mLof a0.250 M KOHsolution are needed to neutralize20.0 mL of the HCl solutionof unknown concentration?

  16. Neutralization Reaction • KOH + HCl  H2O + KCl • HCl is a monoprotic acid

  17. Variables • Ma = X • Va = 20.0 mL • Mb = 0.250 M • Vb = 50.0 mL

  18. Plug and Chug • X (20.0 mL) = (0.250 M) (50.0 mL) • X = 0.625 M = hydrochloric acid

  19. Titration Problem #3 • What is the concentration of a sulfuric acid solutionif 50. mL of a 0.25 M KOHsolution are needed to neutralize20 mL of the H2SO4 solutionof unknown concentration?

  20. Neutralization Reaction • H2SO4 + 2 KOH  2 H2O + K2SO4 • H2SO4 is a diprotic acid • KOH is a monohydroxy base

  21. Variables • Ma = X • Va = 20. mL • Mb = 0.25 M • Vb = 50. mL

  22. Plug and Chug • X (20.) = (0.25 M) (50. mL) • X = 0.625 M = MH+1 (sulfuric acid) • To calculate the Molarity of the H2SO4, adjust for the fact that the acid is diprotic

  23. [H+] vs. [H2SO4] • H2SO4 2H+1 + SO4-2 • Molarity of H2SO4 = ½ [H+1] • ½ (0.625 M) = 0.31 M H2SO4

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