Ch. 19 – Acids & BasesCh. 19 – Acids & Bases

II. pH

(p. 644 – 658)

A. Ionization of WaterA. Ionization of Water

H2O + H2O H3O+ + OH-

Self-Ionization of Water

Ion Product Constant for Water

• For all aqueous solutions, the product of the hydrogen-ion concentration and the hydroxide-ion concentration equals 1.0 x 10-14

• The ion production of water, Kw = [H3O+][OH–]

• Pure water contains equal concentrations of H+ and OH– ions, so [H3O+] = [OH–]

A. Ionization of WaterA. Ionization of Water

Kw = [H3O+][OH-] = 1.0 10-14

A. Ionization of WaterA. Ionization of Water

Find the hydroxide ion concentration of 3.0 10-2 M HCl.

[H3O+][OH-] = 1.0 10-14

[3.0 10-2][OH-] = 1.0 10-14

[OH-] = 3.3 10-13 M

HCl → H+ + Cl-

3.0 10-2M 3.0 10-2M

A. Ionization of WaterA. Ionization of Water

Find the hydronium ion concentration of 1.4 10-3 M Ca(OH)2.

[H3O+][OH-] = 1.0 10-14

[H3O+][2.8 10-3] = 1.0 10-14

[H3O+] = 3.6 10-12 M

Ca(OH)2 → Ca2+ + 2 OH-

1.4 10-3M 2.8 10-

3M

pH = -log[H3O+]

B. pH ScaleB. pH Scale

0

7INCREASING

ACIDITY NEUTRALINCREASING

BASICITY

14

pouvoir hydrogène (Fr.)“hydrogen power”

B. pH ScaleB. pH Scale

pH of Common SubstancespH of Common SubstancespH of Common SubstancespH of Common Substances

B. pH ScaleB. pH Scale

pH = -log[H3O+]

pOH = -log[OH-]

pH + pOH = 14

B. pH ScaleB. pH Scale

What is the pH of 0.050 M HNO3?

pH = -log[H3O+]

pH = -log[0.050]

pH = 1.30

Acidic or basic?Acidic

B. pH ScaleB. pH Scale

What is the pH of 0.050 M Ba(OH)2?

[OH-] = 0.100 M

pOH = -log[OH-]

pOH = -log[0.100]

pOH = 1.00

pH = 13.00

Acidic or basic? Basic

B. pH ScaleB. pH Scale

What is the molarity of HBr in a solution that has a pOH of 9.60?

pH + pOH = 14

pH + 9.60 = 14

pH = 4.40

Acidic

pH = -log[H3O+]

4.40 = -log[H3O+]

-4.40 = log[H3O+]

[H3O+] = 4.0 10-5 M HBr

C. pH Worksheet #6C. pH Worksheet #6

A swimming pool has a volume of one million liters. How many grams of HCl would need to be added to that swimming pool to bring the pH down from 7.0000 to 4.0000? (Assume the volume of the HCl is negligible)

7 = -log[H+]-7 = log[H+]

[H+] = 1 x 10-7 M

-4 = log[H+][H+] = 1 x 10-4 M

= 100 mol H+

1,000,000LSol’n

1x10-4

mol H+

1 L soln

= 0.1 mol H+

1,000,000LSol’n

1x10-7

mol H+

1 L soln

C. pH Worksheet #6C. pH Worksheet #6

100 mol H+ – 0.1 mol H+= 99.9 mol HCl

= 3642 g HCl99.9 mol HCl 36.46 g HCl

1 mol HCl

A swimming pool has a volume of one million liters. How many grams of HCl would need to be added to that swimming pool to bring the pH down from 7.0000 to 4.0000? (Assume the volume of the HCl is negligible)

D. pH Sig FigsD. pH Sig Figs

For the pH, the number of sig figs is shown by the # of decimal places• [H+] = 2.26 x 10-4 M =>

For the molarity from the pH, check decimal places in the pH• pH = 4.25 =>

pH = 3.646

5.6 x 10-5 M