1. Ph Equals the Negative Log of the Concentration of H3O+ À Ph = -Log H3O+

pH SCALE

The pH scale was developed as a measure of the concentration of H+ ions in a solution. 0 is strongly acidic, 7 is neutral, and 14 is strongly basic. It is a logarithmic scale.

+ + 1. pH equals the negative log of the concentration of H3O  pH = -log[H3O ]

+ -14 a. Example: If [H3O ] ions in a solution is 10 , the pH is 14 2. pOH equals the negative log of the concentration of OH-  pH = -log[OH-] 3. At 25˚C pH + pOH = 14

In water, there is an equal number of H+ and OH- ions: HOH ↔ H+ + OH- What does LeChatelier’s principle tell us will happen to the concentration of hydroxide ions if the concentration of hydrogen ions increases? It will decrease. So, the concentrations of the ions created by basic and acidic solutions are inversely related. When [H+] > [OH-] the solution is acidic then, and the reverse is true for a basic solution. pH Calculations

1. + If either [H3O ] or pH of a solution is known, the other can be found.

2. + + Calculating pH from [H3O ] or [H ] a. Determine the pH of the following: i. 1x10-3 M HCl pH = 3.0

ii. -12 -12 6.5x10 M HNO3 pH = -log(6.5x10 ) = 11.19

iii. -12 + -12 + 6.5x10 M H2SO4 [H3O ] = 2x6.5x10  pH = -log[H3O ] = 10.99 3. Calculating pH from [OH-]

a. + - -14 The ion product constant (Kw) = [H3O ] x [OH ] = 1.0 x 10 M b. Example: What is the pH of a 1.0 x 10-3 M NaOH solution? pH = 11 c. Find the pH of the following: i. 1 x 10-4 M NaOH pH = 10.0

ii. -2 -14 + -2 1.0x10 M Mg(OH)2 1.0 x 10 = [H3O ] x [2x1.0 x 10 ] 

+ -13 -13 [H3O ] = 5 x 10  pH = -log(5 x 10 ) = 12.3 4. + - Calculating [H3O ] or [OH ] from pH

5. + -pH Rearrange above equation to get [H3O ] = 10 a. Practice:

i. + -4 Determine the [H3O ] in an aqueous solution with a pH of 4.0 1 x 10

ii. + -7.52 -8 If the pH of a solution is 7.52, what is the [H3O ]? 10 = 3.0 x 10 M 1. What is the hydroxide ion concentration? (1x10-14/3x10-8)=3.3x10-7M

- + 2. Is the solution acidic or basic? Basic because [OH ]>[H3O ] 6. Decreasing [H+] means increasing pH a. 10-3 = pH 3, 10-10 = pH 10  10-3 > 10-10 but 3 < 10