1. Titration

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

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

4. Acid-Base Titration • Carefully controlled neutralization reaction • Requiresstandard solution& acid-base indicator • Standard solution is: acid/base of known concentration

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

6. Equivalence point total # moles H+1 ions donated by acid = total # moles 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- 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 with monohydroxy bases • diprotic acids with dihydroxy bases • triprotic acids with trihydroxy bases

11. ≠ # OH’sin base If: # H’sin acid (Ma)(Va) = (Mb)(Vb) need to modify equation: (#H’s) (#OH’s)

12. Titration Problem #1 • In a titration of40.0 mLof a nitric acid solution, the end point isreached when35.0mLof0.100MNaOHis added Calculate the concentration of the nitric acid solution

13. Neutralization Reaction • HNO3 + NaOH  H2O + NaNO3 • HNO3 is a monoprotic acid • NaOH is a monohydroxy base

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

15. Plug and Chug (1)(X) (40.0 mL) = (0.100 M )(35.0mL)(1) X = 0.875 M HNO3

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

17. Neutralization Reaction • KOH + HCl  H2O + KCl • HNO3 is a monoprotic acid • KOH is a monohydroxy base

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

19. Plug and Chug (1)(X)(20.0 mL) = (0.250 M) (50.0 mL)(1) X = 0.625 M HCl

20. Titration Problem #3 • What is the concentration of a sulfuric acid solutionif50.0mL of a 0.25 M KOHsolution is needed to neutralize20.0mL of the H2SO4 solutionof unknown concentration?

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

22. Variables • Ma = X • Va = 20.0mL • Mb = 0.25M • Vb = 50.0mL

23. Plug and Chug (2)(X)(20.0ml) = (0.25M)(50.0ml)(1) X = 0.3125 MH2SO4(sulfuric acid)