1. The Autoionization of Water In water, we constantly have (a little)... H 2 O(l) + H 2 O(l) H 3 O + (aq) + OH – (aq) Thus (@ 25 o C), the eq. const. for water is: K w = [H 3 O + ] [OH – ] = [H + ] [OH – ] = 1.0 x 10 –14 This equation is taken to be valid for pure water and for dilute aqueous solutions, @ 25 o C. [H + ] > [OH – ] [H + ] < [OH – ] [H + ] = [OH – ] BASENEUTRALACID

2. At 25 o C, calculate the hydrogen ion concentration if the hydroxide ion concentration is 2.7 x 10 –4 M. Is this solution an acid or a base? [H + ] [OH – ] = 1.0 x 10 –14 [H + ] (2.7 x 10 –4 ) = 1.0 x 10 –14 [H + ] = 3.7 x 10 –11 M [H + ] < [OH – ] base

3. The pH Scale Definition of pH... 0 ACID 7 BASE 14 -- A change of 1 pH unit means that [H + ] (and [OH – ]) has changed by a factor of ___. 10 A solution with pH 2 is how many times more acidic than one with pH 5? pH = –log [H 3 O + ] = –log [H + ] as [H + ] /, pH / neutral 1000X more acidic (i.e., 1000X less basic) Soren Sorensen (1868–1939) :

4. Especially in biochemical reactions, the rate law is often dependent on the hydrogen ion concentration. If the rate is 1 st order in [H + ], then doubling [H + ] would double the rate. -- Human blood pH is between 7.35 and 7.45. white blood cell platelet red blood cell Scanning electron microscope micrograph of ordinary blood.

5. ** Significant figures rule for logarithms: Find the pH if the hydronium ion concentration is 5.2 x 10 –9 M. Find the pH if the hydroxide ion concentration is 3.9 x 10 –10 M. # of sig. figs. in [ ] = # of decimal places in pH pH = –log [H 3 O + ]= –log (5.2 x 10 –9 )= 8.28 [H + ] [OH – ] = 1.0 x 10 –14 3.9 x 10 –10 So [H + ] = 2.56 x 10 –5 M pH = –log [H + ]= –log (2.56 x 10 –5 )= 4.59 Blueberries grow best in soil having a pH between 4.5 and 5.0.

6. pOH = –log [OH – ] Other equations: Find [H + ] if the pH = 5.22. [OH – ] = 10 –pOH [H + ] = 10 –pH pH + pOH = 14 [H + ] = 10 –pH = 10 –5.22 = 6.0 x 10 –6 M

7. pOH = –log [OH – ] Other equations: Find [H + ] if the pH = 5.22. [OH – ] = 10 –pOH [H + ] = 10 –pH pH + pOH = 14 [H + ] = 10 –pH = 10 –5.22 = 6.0 x 10 –6 M

8. Measuring pH pH meter acid-base indicators: e.g., pH paper is paper impregnated with mixtures of various indicators. a pair of electrodes chemicals whose color depends on pH litmus, phenolphthalein, bromthymol blue, methyl red, methyl orange Bromthymol blue is yellow at pH < 6.0 and blue at pH > 7.6.