1. Chapter 6 Problems 6-29, 6-31, 6-39, 6.41, 6-42, 6-48,

2. Outline Equilibrium of Acids and Bases Bronsted-Lowry Acids/Bases Define strong Define weak pH of pure water at 25 o C Define K a and K b Relationship b/w K a and K b Chapter 8 – Activity Relationship with K

3. Equilibrium Acids and Bases & Equilibrium Section 6-7

4. Strong Bronsted-Lowry Acid A strong Bronsted-Lowry Acid is one that donates all of its acidic protons to water molecules in aqueous solution. (Water is base – electron donor or the proton acceptor). HCl as example

5. Strong Bronsted-Lowry Base Accepts protons from water molecules to form an amount of hydroxide ion, OH -, equivalent to the amount of base added. Example: NH 2 - (the amide ion)

7. Question Can you think of a salt that when dissolved in water is not an acid nor a base? Can you think of a salt that when dissolved in water IS an acid or base?

8. Weak Bronsted-Lowry acid One that DOES not donate all of its acidic protons to water molecules in aqueous solution. Example? Equilibrium

9. Weak Bronsted-Lowry base Does NOT accept an amount of protons equivalent to the amount of base added, so the hydroxide ion in a weak base solution is not equivalent to the concentration of base added. example: NH 3

10. Common Classes of Weak Acids and Bases Weak Acids carboxylic acids ammonium ions Weak Bases amines carboxylate anion

11. Question: Question: Calculate the Concentration of H + and OH - in Pure water at 25 0 C. Equilibrium and Water

12. EXAMPLE: Calculate the Concentration of H + and OH - in Pure water at 25 0 C. H 2 O H + + OH - Initialliquid-- Change-x+x Equilibrium Liquid-x +x K W = (X)(X) = ? K w = [H + ][OH - ] = ?

14. EXAMPLE: Calculate the Concentration of H + and OH - in Pure water at 25 0 C. H 2 O H + + OH - Initialliquid-- Change-x+x Equilibrium Liquid-x +x K W = (X)(X) = 1.01 X 10 -14 K w = [H + ][OH - ] = 1.01 X 10 -14 (X) = 1.00 X 10 -7

15. Example What is the concentration of OH - in a solution of water that is 1.0 x 10 -3 M in [H + ] (@ 25 o C)? K w = [H + ][OH - ] 1.0 x 10 -14 = [1 x 10 -3 ][OH - ] 1.0 x 10 -11 = [OH - ] “From now on, assume the temperature to be 25 o C unless otherwise stated.”

16. pH ~ -3 -----> ~ +16 pH + pOH = - log K w = pK w = 14.00

17. Is there such a thing as Pure Water? In most labs the answer is NO Why? A century ago, Kohlrausch and his students found it required to 42 consecutive distillations to reduce the conductivity to a limiting value. CO 2 + H 2 O HCO 3 - + H +

18. Weak Acids and Bases HA H + + A - HA + H 2 O (l) H 3 O + + A - KaKa K a ’ s ARE THE SAME

19. Weak Acids and Bases B + H 2 O BH + + OH - KbKb

20. Relation Between K a and K b

21. Relation between Ka and Kb Consider Ammonia and its conjugate acid. NH 3 + H 2 O NH 4 + + OH - KbKb NH 4 + + H 2 O NH 3 + H 3 O + KaKa H 2 O + H 2 O OH - + H 3 O +

22. Example The K a for acetic acid is 1.75 x 10 -5. Find K b for its conjugate base. K w = K a x K b

23. Example Calculate the hydroxide ion concentration in a 0.0100 M sodium hypochlorite solution. OCl - + H 2 O  HOCl + OH - The acid dissociation constant = 3.0 x 10 -8

24. 1 st Insurance Problem Challenge on page 120

25. Chapter 8 Activity

26. Write out the equilibrium constant for the following expression Fe 3+ + SCN -  Fe(SCN) 2+ Q: What happens to K when we add, say KNO 3 ? A: Nothing should happen based on our K, our K is independent of K + & NO 3 -

27. K decreases when an inert salt is added!!! Why? K eq

28. 8-1 Effect of Ionic Strength on Solubility of Salts Consider a saturated solution of Hg 2 (IO 3 ) 2 in ‘pure water’. Calculate the concentration of mercurous ions. Hg 2 (IO 3 ) 2(s)  Hg 2 2+ + 2IO 3 - K sp =1.3x10 -18 seemingly strange effect A seemingly strange effect is observed when a salt such as KNO 3 is added. As more KNO 3 is added to the solution, more solid dissolves until [Hg 2 2+ ] increases to 1.0 x 10 -6 M. Why? ICE some- - -x+x+2x some-x+x+2x

29. Increased solubility Why? LeChatelier’s Principle? NO – not a product nor reactant Complex Ion? No Hg 2 2+ and IO 3 - do not form complexes with K + or NO 3 -. How else?

30. The Explanation Consider Hg 2 2+ and the IO 3 - - 2+ Electrostatic attraction

31. The Explanation Consider Hg 2 2+ and the IO 3 - 2+ Electrostatic attraction - The Precipitate!! Hg 2 (IO 3 ) 2 (s) The Precipitate!!

32. The Explanation Consider Hg 2 2+ and the IO 3 - - 2+ Electrostatic attraction Add KNO 3 NO 3 - K+

33. The Explanation Consider Hg 2 2+ and the IO 3 - - 2+ Add KNO 3 K+ NO 3 - K+

34. The Explanation Consider Hg 2 2+ and the IO 3 - 2+ NO 3 - Hg 2 2+ and IO 3 - can’t get CLOSE ENOUGH to form Crystal lattice Or at least it is a lot “Harder” to form crystal lattice - K+

36. The potassium hydrogen tartrate example

37. Alright, what do we mean by Ionic strength? Ionic strength is dependent on the number of ions in solution and their charge. Ionic strength (  ) = ½ (c 1 z 1 2 + c 2 z 2 2 + …) Or Ionic strength (m) = ½  c i z i 2

38. Examples Calculate the ionic strength of (a) 0.1 M solution of KNO 3 and (b) a 0.1 M solution of Na 2 SO 4 (c) a mixture containing 0.1 M KNO 3 and 0.1 M Na 2 SO 4. (  ) = ½ (c 1 z 1 2 + c 2 z 2 2 + …)

39. Alright, that’s great but how does it affect the equilibrium constant? Activity = A c = [C]  c AND

40. Relationship between activity and ionic strength Debye-Huckel Equation 2 comments  = ionic strength of solution  = activity coefficient Z = Charge on the species x  = effective diameter of ion (nm) (1)What happens to  when  approaches zero? (2)Most singly charged ions have an effective radius of about 0.3 nm Anyway … we generally don’t need to calculate  – can get it from a table

41. Activity coefficients are related to the hydrated radius of atoms in molecules

42. Relationship between  and 

45. Back to our original problem Consider a saturated solution of Hg 2 (IO 3 ) 2 in ‘pure water’. Calculate the concentration of mercurous ions. Hg 2 (IO 3 ) 2(s)  Hg 2 2+ + 2IO 3 - K sp =1.3x10 -18 At low ionic strengths  -> 1

46. Back to our original problem Consider a saturated solution of Hg 2 (IO 3 ) 2 in ‘pure water’. Calculate the concentration of mercurous ions. Hg 2 (IO 3 ) 2(s)  Hg 2 2+ + 2IO 3 - K sp =1.3x10 -18 In 0.1 M KNO 3 - how much Hg 2 2+ will be dissolved?

47. Back to our original problem Consider a saturated solution of Hg 2 (IO 3 ) 2 in ‘pure water’. Calculate the concentration of mercurous ions. Hg 2 (IO 3 ) 2(s)  Hg 2 2+ + 2IO 3 - K sp =1.3x10 -18