© Copyright Pearson Prentice Hall Strength of Acids and Bases > Slide 1 of 27 Strong and Weak Acids and Bases How does the value of an acid dissociation constant relate to the strength of an acid? 19.3

Slide 2 of 27 © Copyright Pearson Prentice Hall Strength of Acids and Bases > Strong and Weak Acids and Bases An acid dissociation constant (K a ) is the ratio of the concentration of the dissociated (or ionized) form of an acid to the concentration of the undissociated (nonionized) form. 19.3

© Copyright Pearson Prentice Hall Slide 3 of 27 Strength of Acids and Bases > Strong and Weak Acids and Bases Weak acids have small K a values. The stronger an acid is, the larger is its K a value. 19.3

Slide 4 of 27 © Copyright Pearson Prentice Hall Strength of Acids and Bases > Strong and Weak Acids and Bases Strong acids are completely ionized in aqueous solution. Weak acids ionize only slightly in aqueous solution. 19.3

Slide 5 of 27 © Copyright Pearson Prentice Hall Strength of Acids and Bases > Calculating Dissociation Constants 19.3

Slide 6 of 27 © Copyright Pearson Prentice Hall Strength of Acids and Bases > Strong and Weak Acids and Bases In general, the base dissociation constant (K b ) is the ratio of the concentration of the conjugate acid times the concentration of the hydroxide ion to the concentration of the base. 19.3

Slide 7 of 27 © Copyright Pearson Prentice Hall Strength of Acids and Bases > Strong and Weak Acids and Bases Strong bases dissociate completely into metal ions and hydroxide ions in aqueous solution. Weak bases react with water to form the hydroxide ion and the conjugate acid of the base. 19.3

Slide 8 of 27 © Copyright Pearson Prentice Hall Strength of Acids and Bases > Strong and Weak Acids and Bases 19.3

© Copyright Pearson Prentice Hall Slide 9 of Section Quiz. 1. H 2 S is considered to be a weak acid because it a.is insoluble in water. b.ionizes only slightly. c.is completely ionized. d.is dilute.

© Copyright Pearson Prentice Hall Slide 10 of Section Quiz. 2. Calcium hydroxide, Ca(OH) 2, is a strong base because it a.has a large K b. b.has a small K b. c.forms concentrated solutions. d.is highly soluble in water.

© Copyright Pearson Prentice Hall Slide 11 of Section Quiz. 4. The K a of three acids is given below. (1) 5.1  10 –3 (2) 4.8  10 –11 (3) 6.3  10 –5 Put the acids in order from the strongest acid to the weakest acid. a.1, 3, 2 b.2, 3, 1 c.3, 1, 2 d.2, 1, 3

© Copyright Pearson Prentice Hall Slide 12 of The K b of four bases is given below. (1) 7.41 x (2) 1.78 x (3) 4.27 x (4) 4.79 x Put the bases in order from the strongest base to the weakest base. a.2, 3, 4, 1 b.2, 1, 3, 4 c.4, 3, 1, 2 d.1, 4, 3, Section Quiz.

© Copyright Pearson Prentice Hall Slide 13 of Section Quiz. 3. If the [H + ] of a 0.205M solution of phenol (C 6 H 5 OH) at 25ºC is  10 -6, what is the K a for phenol? Phenol is monoprotic. a. K a = 2.67 x b. K a = 1.14 x c. K a = 5.48 x d. K a = 1.53 x 10 -3

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