1. What is pH?

2. Ion Product Constant for Water  H 2 O(l)  H + (aq) + OH - (aq)  Keq = Kw = [H + ] x [OH - ]  The ion product constant for water (Kw) is the equilibrium constant (Keq) expression for the self-ionization of water.  Kw = 1 x 10 -14 at 298K.

3.  H 2 O(l)  H + (aq) + OH - (aq)  Keq = Kw = [H + ] x [OH - ] = 1 x 10 -14  [H + ] > [OH - ] = acidic  [H + ] < [OH - ] = basic  [H + ] = [OH - ] = neutral

4. Calculations of [H+] or [OH-]  Ex 1: At 298 K the H + ion concentration of an aqueous solution is 1.0 x 10 -5 M. What is the OH - ion concentration in the solution? Is the solution acidic, basic, or neutral? Kw = [H + ] x [OH - ] 1 x 10 -14 = [1.0 x 10 -5 ] x [OH - ] 1.0 x 10 -5 1.0 x 10 -9 = [OH - ] [H + ] & [OH - ] comparison 1.0 x 10 -5 > 1.0 x 10 -9 0.00001 > 0.000000001 [H + ] > [OH - ] = solution is acidic

5. Calculations of [H+] or [OH-]  Ex 2: At 298K the H + ion concentration of an aqueous solution is 2.5 x 10 -6 M. What is the OH - ion concentration in the solution? Is the solution acidic, basic, or neutral? Kw = [H + ] x [OH - ] 1 x 10 -14 = [2.5 x 10 -6 ] x [OH - ] 2.5 x 10 -6 4.0 x 10 -9 = [OH - ] [H + ] & [OH - ] comparison 2.5 x 10 -6 > 4.0 x 10 -9 0.0000025 > 0.000000004 [H + ] > [OH - ] = solution is acidic

6. What is pH?  The hydrogen concentration is cumbersome so Soren Sorensen came up with the pH scale.  pH ranges from 0-14  pH <7 is acidic  pH = 7 is neutral  pH > 7 is basic pH= -log[H + ] ***Always use pH to identify if a solution is acidic, neutral or basic, NOT pOH

7. What is pH?

8.  We use logarithms to do this  N = 10 x, then log N = x  pH = -log[H + ]  Ex3: What is the pH of a solution with a concentration of 1.0 x 10 -6 hydrogen ions? Then tell if it is acidic, neutral or basic. pH = -log[H + ] pH = -log[1.0 x 10 -6 ] pH = 6.0 pH is acidic ***There is a shortcut to this, look at the eponent for the given concentration, and that is your pH or pOH depending on which concentration is given

9.  pH = -log[H + ]  Ex 4: What is the pH of a solution if the concentration of the hydroxide ions is 9.6 x 10 -4 M? Then tell if it is acidic, neutral or basic. Kw = [H + ] x [OH - ] 1 x 10 -14 = [H + ] x [9.6 x 10 -4 ] 9.6 x 10 -4 1.0 x 10 -11 = [H + ] pH = -log[H + ] pH = -log[1.0 x 10 -11 ] pH = 11 pH > 7 is basic

10. pOH = -log[OH - ] pH + pOH = 14  Ex 5: Ammonia gas has a hydroxide-ion concentration of 4.0 x10 -3 M. Calculate the pOH and pH at 298 K. Then tell if it is acidic, neutral or basic. pOH = 3 (from the exponent) pH + pOH = 14 pH + 3 = 14 pH = 11 pH > 7 is basic 11 > 7 Ammonia solution is basic

11.  pOH = -log[OH - ] or pH + pOH = 14  Ex 6: A solution contains a hydrogen ion concentration of 3.56 x 10 -8 M. Calculate the pH and pOH at 298 K. Then tell if it is acidic, neutral or basic. pH = 8 pH + pOH = 14 8+ pOH = 14 pOH = 6 pH > 7 is basic 8 > 7 solution is basic