1. PH

2. Ionization of Water  When compounds dissociate/ionize in an aqueous solution, they produce ions - hydronium (H 3 O + ) and hydroxide (OH - )  These ion concentrations can be expressed more easily as [H 3 O + ] = 1.0 x 10 - 7 M and [OH - ] = 1.0 x 10 - 7 M.  The brackets indicate “concentration of” in Molarity (M).

3. Kw  The product of [H 3 O + ] and [OH - ] is equal to 1.0 x 10 - 14 M 2, which is a constant known as the ionization constant of water, K W.  Because the [H 3 O + ] and [OH - ] in pure water are equal, pure water is neutral.  Any substance whose [H 3 O + ] does not equal its [OH - ] is going to be acidic or basic.

4. Calculating Kw  To calculate either the acid of base concentration, you must know how to rearrange the K W equation.

5. Example  What is the [H 3 O + ] if [OH - ] = 4.56 x 10 - 8 M?  [H 3 O + ] = ?  [OH - ] = 4.56 x 10 - 8 M

6. pH Scale pH of Common Substances

7. pH Equations  A more convenient way of expressing the acidity (or basicness) of a solution is pH and pOH. pH = -log[H 3 O + ] pOH = -log[OH - ] pH + pOH = 14 pH values from 0 - 6.9 are acidic 7.1 - 14 are basic 7.0 is neutral pOH values from 0 - 6.9 are basic 7.1 - 14 are acidic 7.0 is neutral.

8. pH Example  What is the pH of 0.050 M HNO 3 ? pH = -log[H 3 O + ] pH = -log[0.050] pH = 1.3 Acidic or basic? Acidic

9. pOH Example  What is the pOH of 0.070 M NH 3 ? Is it acidic or basic? pOH = -log[OH - ] pOH = -log[0.070] = 1.15 It is basic because 1.15  7.

10. Example pH (pOH) calculations  If you had a solution with the concentration of 0.025 M [H 3 O + ], what is the solutions pH? What is the solutions pOH? Given: [H 3 O + ] = 0.025 M Unknown: pH = ? pH = -log [H 3 O + ] = -log[0.025M] = 1.6 pOH = 14 – pH = 14 - 1.6 = 12.4

11. Example pH (pOH) calculations  What is the pH of a 1.5 M solutions of KOH? (this is a base) Given: [1.5 M] Unknown: pH = ? pOH = - log [OH - ] pOH = - log [1.5] pOH = -0.18 pH + pOH = 14 14 – pOH = pH 14- (-0.18) = 14.18 pH = 14.18 Check : Answer does indicate that KOH forms a sol’n pH  7, which is basic.

12. Converting pH & pOH to Concentrations  If you want to know the [H 3 O + ] or [OH - ] from a given pH or pOH value, use the following equations:  Example: What is the [OH - ] if the pH = 12.27 ?  pH = 12.27  pOH = ?  [OH - ] = ? [H 3 O + ] = 10 -pH