1. pH SCALE Chemistry

2. Dissociation  Water will split apart to give a H +1 ion and an OH -1 ion. H 2 O (l)  H +1 (aq) + OH -1 (aq) The equilibrium constant for this is K w (like K sp ) K w = [H +1 ] x [OH -1 ] = 1.0 x 10 -14 No matter how much of H +1 or OH -1 present, this will always be true. Why?

3.  If the [H +1 ] is 0.1 M what is the [OH -1 ]? K w = [H +1 ] x [OH -1 ] = 1.0 x 10 -14 so: 1.0 x 10 -14 = (0.1) x [OH -1 ] [OH -1 ] = 1.0 x 10 -14 / 0.1 = 1.0 x10 -13 What happens if I mix 0.1 M [H +1 ] and 0.1 M [OH -1 ]? Problem: Calculate the [OH -1 ] if the [H +1 ] is 0.005 M

4. pH Scale

5.  pH = -log 10 [H + ]  [H + ] = 10 -pH  Scale is logarithmic  Every step in pH is factor of 10 of [H + ]  Example: pH = 3  [H + ] = 1 x 10 -3 M pH = 4  [H + ] = 1 x 10 -4 M  Low pH  More Acidic!  High pH  More Basic!

6. pH Calculations  Determine the pH of a solution that has [H + ] = 3 x 10 -5 M.  What is the pH of concentrated HCl? ([H + ] = 1.0 M)  Determine the [H+] of a solution with pH = 8.5.  What is the [H + ] of concentrated H 2 SO 4 (pH = -18)?

7. [OH - ]  Water breaks down into H + & OH -  H 2 O  H + + OH -  [H + ] x [OH - ] = 10 -14  Low pOH  More Basic  High pOH  More Acidic

8. More Math Questions  What is the pH of a 1 M NaOH solution? ([OH - ] = 1.0 M)  Determine the [H+] of a 0.05 M KOH solution. ([OH - ] = 0.05 M)

9. Measuring pH  pH often measured with a pH probe  Can be measured with an acid/base indicator such as universal indicator

10. pH Indicators  pH Indicators  Change color at a certain pH HIn  H + + In -

11. Natural pH Indicators  Natural pH indicators occur in nature:  Blueberries, Red Cabbage, Tumeric, etc. In acidic soils, hydrangeas produce blue flowers. In basic soils, hydrangeas produce pink flowers.

12. pH Meters  Place a probe in solution  Usually accurate to about 0.01 pH unit  Detects H + ions electrically

13. Questions… 1. Solution X has a pH of 10. Solution Y has a pH of 7. How many times greater is the [H + ] X than [H + ] Y ? 2. [OH-] = 0.001 M, determine: 1. pH 2. [H + ] 3. Which one gives the highest pH? a) 1 M HCl b) 1 M CH 3 COOH c) 1 M NH 3 d) 1 M NaOH