1 / 12

What is pH?

What is pH?. Ion Product Constant for Water. H 2 O(l)  H + (aq) + OH - (aq) Keq = Kw = [H + ] x [OH - ] = 1 x 10 -14 The ion product constant for water (Kw) is the equilibrium constant expression for the self-ionization of water. The value is dependent upon temperature

barbara-beasley
Download Presentation

What is pH?

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. What is pH?

  2. Ion Product Constant for Water • H2O(l)  H+(aq) + OH-(aq) • Keq = Kw = [H+] x [OH-] = 1 x 10-14 • The ion product constant for water (Kw) is the equilibrium constant expression for the self-ionization of water. • The value is dependent upon temperature • Kw = 1 x 10-14 at 298K

  3. Ion Product Constant for Water Cont. • From this you can calculate the hydrogen ion concentration or the hydroxide concentration. • 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. 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 10-5 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. 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 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 scale ranges from 0-14 • pH <7 is acidic • pH = 7 is neutral • pH > 7 is basic

  7. What is pH?

  8. Calculating pH from [H+] • We use logarithms to do this • N = 10x, 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

  9. Calculating pH from [H+] Cont. • 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 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. Calculating pOH • 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 = -log[OH-] pOH = -log[4.0 x 10-3 ] pOH = 2.4 pH + pOH = 14 pH + 2.4 = 14 pH = 11.6 pH > 7 is basic 11.6 > 7 Ammonia solution is basic

  11. Calculating pH and pOH • 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 = -log[H+] pH = -log[3.56 x 10-8 M] pH = 7.45 pH + pOH = 14 7.45+ pOH = 14 pOH = 6.55 basic pH > 7 is basic 7.45 > 7 solution is basic

More Related