1. Lecture 193/14/05 Spring Break Quiz Seminar today

2. Building a titration curve via calculations Comparison of a titration of a strong acid vs. a weak acid Regionx-axis (mL of acid/base) 0.1 M NaOH y-axis (pH) 100 mL of 0.1 M HCl y-axis (pH) 100 mL of 0.1 M HF Initial pH 01 Before the equivalence point (1/2 equiv. point) 501.47 equivalence point 1007 After the equivalence point 15012.3

5. Initial pH (NaOH titrating HF) K a = 6.8 x 10 -4 HF ↔ F - + H + I0.100 C-X+X E0.1 - XXX

6. Building a titration curve via calculations Comparison of a titration of a strong acid vs. a weak acid Region x-axis (mL of acid/base) 0.1 M NaOH y-axis (pH) 100 mL of 0.1 M HCl y-axis (pH) 100 mL of 0.1 M HF Initial pH 012.10 Before the equivalence point (1/2 equiv. point) 501.47 equivalence point 1007 After the equivalence point 15012.3

8. Equivalence point (NaOH titrating HF) X-axis moles OH - added = moles H 3 O + in solution C OH V OH = C H V H (0.1 M)V OH = (0.1 M)(100 mL) V OH = 100 mL Y-axis Neutralization of weak acid by strong base pH > 7

9. Initial pH (NaOH titrating HF) K a = 6.8 x 10 -4 H 2 O + F - ↔ HF + OH - I0.0500 C-X+X E0.05 - XXX HF + OH - ↔ F - + H 2 O 0.01 moles 0.01 moles 0 moles 0 moles 0.moles 0.01 moles pOH = 6.07 pH = 7.93

10. Building a titration curve via calculations Comparison of a titration of a strong acid vs. a weak acid Region x-axis (mL of acid/base) 0.1 M NaOH y-axis (pH) 100 mL of 0.1 M HCl y-axis (pH) 100 mL of 0.1 M HF Initial pH 012.10 Before the equivalence point (1/2 equiv. point) 501.47 equivalence point 10077.93 After the equivalence point 15012.3

12. ½ Equivalence point (NaOH titrating HF) X-axis moles OH - added = ½ moles H 3 O + in solution V equivalence = 100 mL, so V 1/2equivalence = 50 mL Y-axis HF + OH -  F - + H 2 O (0.1 L)(0.1 M) (0.05 L)(0.1 M) 0.01 moles 0.005 moles 0 moles 0.005 moles 0 moles 0.005 moles pH = pK a Always true for titrations of either weak acids or weak bases

13. Building a titration curve via calculations Comparison of a titration of a strong acid vs. a weak acid Region x-axis (mL of acid/base) 0.1 M NaOH y-axis (pH) 100 mL of 0.1 M HCl y-axis (pH) 100 mL of 0.1 M HF Initial pH 012.10 Before the equivalence point (1/2 equiv. point) 501.473.16 equivalence point 10077.93 After the equivalence point 15012.3

15. After Equivalence point (NaOH titrating HF) X-axis Can pick any volume greater than V equivalence Often pick 3/2 equivalence volume = 150 mL Y-axis HF+ OH -  F - + H 2 O (0.1 L)(0.1 M) (0.15 L)(0.1 M) 0.01 moles 0.015 moles 0 0 moles 0.005 moles 0.01 moles pH is dominated by excess OH - Total volume = volume of acid solution + volume of base added = 250 mL pOH = -log (0.005 moles/0.25 L) = 1.7 pH = 14 – 1.7 = 12.3

16. Building a titration curve via calculations Comparison of a titration of a strong acid vs. a weak acid Region x-axis (mL of acid/base) 0.1 M NaOH y-axis (pH) 100 mL of 0.1 M HCl y-axis (pH) 100 mL of 0.1 M HF Initial pH 012.10 Before the equivalence point (1/2 equiv. point) 501.473.16 equivalence point 10077.93 After the equivalence point 15012.3