16.6 – 16.8 Student Notes

III. Self-Ionization of Water and pH

A. Self-Ionization of Water

1. Self ionization – autoionization –

2. Ion-product constant for water –

3. K_w = [H₃O⁺] [ OH^-] =

Concentrations in pure water should be equal giving us 1.0 x 10^-7 M. If you add an acid or base to water, then

B. Solutions of a Strong Acid or Base

1. LeChatelier’s Principle still holds true. Explain.

2. In a solution of strong acid, you can usually ignore the self-ionization of water; although

3. The reverse is true for a strong base and the hydronium ion concentration

4. Calculating Concentrations of H₃O⁺ and OH^- in Solutions of a Strong Acid or Base

Calculate the concentrations of hydronium ion and hydroxide ion at 25° C in:

a. 0.15 M HNO₃

b. 0.010 M Ca(OH)₂

C. Trends of concentrations

1. In an acidic solution, [H₃O⁺]

2. In a neutral solution, [H₃O⁺]

3. In a basic solution, [H₃O⁺]

D. The pH of a Solution

1. pH –

2. pH =

*Note the number of places after the decimal point in the pH equals the number of significant figures reported in the hydronium-ion concentration

3. Acids à

Neutral à

Bases à

4. Calculating the pH from the hydronium-ion concentration

A sample of orange juice has a hydronium-ion concentration of 2.9 x 10^-4 M. What is the pH? Is the solution acidic?

5. Calculating the hydronium-ion concentration from the pH

The pH of human arterial blood is 7.40. What is the hydronium-ion concentration?

6. pH Meter

How does it work?

7. Acid base indicators

How does it work?

8. You have solutions of NH₃, HCl, NaOH, and HC₂H₃O₂ (acetic acid), all with the same solute concentrations. Rank these in order of pH, from the highest to the lowest.