1. Chapter 16: Acid Base Equilibria and Solubility Equilibria Common Ion Effects Buffers Titration Solubility

2. Chapter 16: Common Ion Effects (1) Apply LeChatelier’s Principle. Would a common ion affect pH NH 3(aq) + H 2 O ↔ NH 4 + (aq) + OH - (aq) –Then Add the Common Ion NH 4 Cl(s)  NH 4 + (aq) + Cl - (aq)

3. Chapter 16: Common Ion Effects (2) What would happen to the pH of the weak acid solution given below if a common ion were added? HC 2 H 3 O 2(aq ↔ H + (aq) + C 2 H 3 O 2 - (aq) –Then Add a common Ion NaC 2 H 3 O 2  Na + (aq) + C 2 H 3 O 2 - (aq)

4. Sample Calculation (1) Calculate the pH of a 0.2 M solution of HC 2 H 3 O 2. Ka = 1.8E-5 (2) Addition of a common ion, C 2 H 3 O 2 -,would have which effect on the pH of the weak acid? Calculate the pH when the solution is made 0.1 M in C 2 H 3 O 2 -

5. Chapter 16: Buffer Solutions Definition A buffer solution maintains a relatively constant pH. Neutralizes any added/created acid. Neutralizes any added/created base.

6. Buffer Combinations (1)Weak Base and Salt with Common Ion : NH 3(aq) + H 2 O ↔ NH 4 + (aq) + OH - (aq) NH 4 Cl(s)  NH 4 + (aq) + Cl - (aq) (2)Weak Acid and Salt with Common Ion HC 2 H 3 O 2(aq ↔ H + (aq) + C 2 H 3 O 2 - (aq) NaC 2 H 3 O 2  Na + (aq) + C 2 H 3 O 2 - (aq)

7. Problem 16.12: Page 758 Which of the following solutions can act as a buffer? (a)KCN & HCN (b)Na 2 SO 4 &NaHSO 4 (c)NH 3 & NH 4 NO 3 (d)NaI & HI

8. Table 15.3

9. Buffer Calculations A 0.2M solution of HC 2 H 3 O 2 is made 0.4 M in NaC 2 H 3 O 2. Calculate the pH of this solution. Ka = 1.8E-5. HC 2 H 3 O 2(aq ↔ H + (aq) + C 2 H 3 O 2 - (aq) NaC 2 H 3 O 2  Na + (aq) + C 2 H 3 O 2 - (aq)

10. Buffer Calculations A 0.2M solution of HC 2 H 3 O 2 is made 0.1 M in NaC 2 H 3 O 2. Calculate the pH of this solution. Ka = 1.8E-5. HC 2 H 3 O 2(aq ↔ H + (aq) + C 2 H 3 O 2 - (aq) NaC 2 H 3 O 2  Na + (aq) + C 2 H 3 O 2 - (aq)

11. Henderson Hasselbach Equation Can calculate pH of a buffer from the K a or K b expression. Or could use the rearrangements of K a or K b called the Henderson Hasselbach pH = pK a + log [common ion]/[weak acid] pOH = pK b + log [common ion]/[weak base]

12. Problem Calculate the pH of a buffer that is 0.12 M in lactic acid (HC 3 H 5 O 3 ) and 0.11 M in sodium lactate (NaC 3 H 5 O 3 ). Ka for lactic acid = 1.4E-4 HC 3 H 5 O 3 ↔ H + (aq + C 3 H 5 O 3 - NaC 3 H 5 O 3  Na + + C 3 H 5 O 3 -

13. Problem How many moles of sodium hypobromite (NaBrO) should be added to 1.00 L of 0.050 M hypobromous acid (HBrO) to form a buffer solution of pH of 9.15. Assume that no volume change occurs when the NaBrO is added. Ka for HBrO is = 2.5E-9

14. Problem (a) What is the ratio of HCO 3 - to H 2 CO 3 in blood of pH 7.4? Ka for H 2 CO 3 = 4.3E-7 (b) What is the ratio of HCO 3 - to H 2 CO 3 in an exhausted marathon runner whose blood pH is 7.1? H 2 CO 3 ↔ H 3 O + + HCO 3 - EQUILIBRIUM IS CONTROLLED BY ENZYME!

15. Problem 16.18: Page 758 Calculate the pH of 1.00 L of the buffer 1.0 M CH 3 COONa/1.OO M CH 3 COOH before and after the addition of: Ka = 1.8E-5 (a)0.080 moles NaOH (b)0.12 moles of HCl

16. Chapter 16: Titration Why Do a Titration? 1. Determination of Concentration of Unknown. Titrate to equivalence point so that can calculate concentration of unknown. Moles acid = moles base indicator

17. Titration: Calculations at Equivalence Point 50 ml of 0.200 M HCl were required to reach the equivalence point when added to 25.0 ml of NaOH. Calculate the concentration of the NaOH. Moles acid = Moles base

18. Acid-Base Titrations Strong Acid-Base Titrations Strong Acid-Base Titrations Consider adding a strong base (e.g. NaOH) to a solution of a strong acid (e.g. HCl).

19. Titration: Calculations at Equivalence Point 50 ml of 0.200 M HCl were required to reach the equivalence point when added to 25.0 ml of NaOH. Calculate the concentration of the NaOH. Moles acid = Moles base

20. Chapter 16: Titration Why Do a Titration? 2. Measure Data for a Titration Curve Can determine Ka or Kb if have weak acid of weak base. Can also calculate the concentration of the unknown acid or base from the titration curve.

21. Acid-Base Titrations Strong Acid-Base Titrations Strong Acid-Base Titrations The plot of pH versus volume during a titration is a titration curve.

22. Acid-Base Titrations Weak Acid-Strong Base Titrations Weak Acid-Strong Base Titrations

24. Titration Curve: Strategy for Titration Calculations (1) Recognize that are calculating pH at a step in a titration. –Volume is constantly changing. Stoichiometry: must work with moles. –Smallest quantity will have completely reacted.

25. Titration Curve: Strategy for Titration Calculations (2) Calculate moles of acid and moles of base. moles = (moles/liter) (volume) moles HC 2 H 3 O 2 = 0.150 moles/liter) (0.035 liters) moles NaOH = (0.150 moles/liter) (0.0175 liters)

26. Titration Curve: Strategy for Titration Calculations (3) If have more moles of acid than base, the acid will determine/control the pH. (4) If have more moles of base than acid, the bases will determine/control the pH. (5) The smaller quantity will completely react and disappear. acid + base  salt + water

27. Titration Curve: Strategy for Titration Calculations (6) If some moles of acid remain, use approach described in chapter 15 to calculate the [H + ]. –First decide if have strong acid or weak acid. –Then calculate [acid]. –[acid] = moles of acid/combined volume. –Then calculate [H + ] and the pH.

28. Titration Curve: Strategy for Titration Calculations (7) If some moles of base remain, use approach described in chapter 18 to calculate the [OH-]. –First decide if have strong base or weak base. –Then calculate [base]. –[base] = moles of base/combined volume

29. Titration Curve: Strategy for Titration Calculations (7) If some moles of base remain, use approach described in chapter 15 to calculate the [OH-]. –First decide if have strong base or weak base. –Then calculate [base]. –[base] = moles of base/combined volume

30. Problem A 20.0 ml sample of 0.200 M HBr is titrated with 0.200 M NaOH solution. Calculate the pH of the solution after the following volumes of base have been added. (b) 19.9 ml

31. Problem Consider the titration of 30.0 ml of 0.030 M NH 3 with 0.025 M HBr. Calculate the pH after the following volumes of titrant have been added. K b = 1.8E-5 (b) 10.0 ml

32. Problem What is the pH of a solution prepared by mixing exactly 30.0 ml of 0.200 M HC 2 H 3 O 2 with 15.0 ml of 0.400 M KOH.

33. Part B: Exp 14-B. Calculate pH of Buffer. (1) Weighed 3.5 g of NaC 2 H 3 O 2. mole= 136 g measured 2.57E-2 moles (2) Measured 8.8 ml of 3.0 M HC 2 H 3 O 2. Ka = 1.8E-5 pKa = -log (1.8E-5) = 4.74 (3) Added 55.6 ml of water. Final volume = 64.4 ml

34. Part B: Exp 14-B. Calculate pH of Buffer. [NaC 2 H 3 O ] = 2.57E-2 moles/0.0556 liters = 0.462 M [HC 2 H 3 O ] = [3.0 moles/liter) (0.0088 liters)/0.0556 liters = 0.474 M pH = pKa + log (0.462/.474) = 4.72

35. Addition of HCl Calculate pH of Buffer Made in 14-B After addition of 1.0 ml of 6.0 M HCl