2Strengths of Acids and Bases 19.3Lemons and grapefruits have a sour taste because they contain citric acid. Sulfuric acid is a widely used industrial chemical that can quickly cause severe burns if it comes into contact with skin. You will learn why some acids are weak and some acids are strong.
3Strong and Weak Acids and Bases 19.3Strong and Weak Acids and BasesStrong and Weak Acids and BasesHow does the value of an acid dissociation constant relate to the strength of an acid?
4Strong and Weak Acids and Bases 19.3Strong and Weak Acids and BasesAn acid dissociation constant (Ka) is the ratio of the concentration of the dissociated (or ionized) form of an acid to the concentration of the undissociated (nonionized) form.
5Strong and Weak Acids and Bases 19.3Strong and Weak Acids and BasesWeak acids have small Ka values. The stronger an acid is, the larger is its Ka value.
6Strong and Weak Acids and Bases 19.3Strong and Weak Acids and BasesStrong acids are completely ionized in aqueous solution.Weak acids ionize only slightly in aqueous solution.
7Strong and Weak Acids and Bases 19.3Strong and Weak Acids and BasesIn general, the base dissociation constant (Kb) is the ratio of the concentration of the conjugate acid times the concentration of the hydroxide ion to the concentration of the base.
8Strong and Weak Acids and Bases 19.3Strong and Weak Acids and BasesStrong 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.
9Strong and Weak Acids and Bases 19.3Strong and Weak Acids and Bases
10Calculating Dissociation Constants 19.3Calculating Dissociation ConstantsCalculating Dissociation ConstantsHow can you calculate an acid dissociation constant (Ka) of a weak acid?
11Calculating Dissociation Constants 19.3Calculating Dissociation ConstantsTo find the Ka of a weak acid or the Kb of a weak base, substitute the measured concentrations of all the substances present at equilibrium into the expression for Ka or Kb.
12Calculating Dissociation Constants 19.3Calculating Dissociation ConstantsAcid Dissociation ConstantThe dissociation constant, Ka, of ethanoic acid is calculated from the equilibrium concentrations of all of the molecules and ions in the solution.
13Calculating Dissociation Constants 19.3Calculating Dissociation ConstantsDissociation of an acid (HA) in water yields H3O+ and A-. The bar graphs compare the extent of dissociation of strong, weak, and very weak acids. INTERPRETING GRAPHS a. Explain In the graph for the strong acid, why are the heights of the H3O+ and A- bars the same as the height of HA bar? b. Inferring In the graph for the weak acid, why is the height of the H3O+ bar the same as the distance from the top of the second HA bar to the dotted line? c. Apply Concepts Draw a bar graph for the dissociation of the weak diprotic acid, oxalic acid. Be sure to include the first and second dissociation.
15Calculating Dissociation Constants 19.3Calculating Dissociation ConstantsBase Dissociation ConstantThe dissociation constant, Kb, of ammonia is calculated from the equilibrium concentrations of all of the molecules and ions in the solution.
16Calculating Dissociation Constants 19.3Calculating Dissociation ConstantsConcentration and Strength
2319.3 Section Quiz.1. H2S is considered to be a weak acid because itis insoluble in water.ionizes only slightly.is completely ionized.is dilute.
2419.3 Section Quiz.2. Calcium hydroxide, Ca(OH)2, is a strong base because ithas a large Kb.has a small Kb.forms concentrated solutions.is highly soluble in water.
2519.3 Section Quiz.3. If the [H+] of a 0.205M solution of phenol (C6H5OH) at 25ºC is 10-6, what is the Ka for phenol? Phenol is monoprotic.Ka = 2.67 x 10-11Ka = 1.14 x 10-5Ka = 5.48 x 10-12Ka = 1.53 x 10-3
2619.3 Section Quiz.4. The Ka of three acids is given below.(1) 5.1 10–3(2) 4.8 10–11(3) 6.3 10–5Put the acids in order from the strongest acid to the weakest acid.1, 3, 22, 3, 13, 1, 22, 1, 3
2719.3 Section Quiz. 5. The Kb of four bases is given below. (1) 7.41 x 10-5(2) 1.78 x 10-5(3) 4.27 x 10-4(4) x 10-4Put the bases in order from the strongest base to the weakest base.2, 3, 4, 12, 1, 3, 44, 3, 1, 21, 4, 3, 2