pH Scale

Logarithmic scale indicating the acidity of a
substance.

Movement from one whole number to the next
represents a change by a power of 10.
Acids: 1-7, [H3O+] > [OH-]
 Neutral: 7, [H3O+] = [OH-]
 Bases: 7-14, [H3O+] < [OH-]


Which pH change represents a hundredfold
increase in the concentration of H3O+?
1. pH 5 to pH 7
2. pH 13 to pH 14
3. pH 3 to pH 1
4. pH 4 to pH 3
pH


Power of hydronium
pH = -log[H+] = -(exponent)
Example 1

Determine the pH of a solution in which
the [H+] = 1.0X10-5 M. Is this solution
acidic or basic?
pH = -log[1.0X10-5] = -(-5) = 5
 The solution is acidic.


Example 2: An unknown solution is found to
have a hydronium ion concentration of 10 M.
Is the solution acidic or basic?

Example 3: What is the hydronium ion
concentration of a solution with a pH of 7?
pOH

Reverse of pH Scale.
Acids: 7-14
 Neutral: 7
 Bases: 1-7

pH + pOH = 14
 pOH = -log[OH-]


Example 4: What is the pOH of a 1.0X10-4 M
NaOH solution?

Example 5: Determine the pOH of a solution
if the pH is 12.

Example 6: What is the pOH of a 0.0001 M
HI solution?