Principles & Modern Applications General Chemistry Principles & Modern Applications 10th Edition Petrucci/Herring/Madura/Bissonnette Chapter 17 Additional Aspects of Acid-Base Equilibria Dr. Wendy Pell University of Ottawa Copyright © 2011 Pearson Canada Inc. Slide 1 of 37

Complete the following acid/base reactions: H2PO4- + H2O ⇌ A + B HPO42- + H2O ⇌ C + D HPO42- + H3O+ ⇌ E + F HPO42- + OH- ⇌ G + H A B C D E F G H 1. HPO42- OH- H2PO4- H2O 2. H3O+ PO4- H3PO4 3. PO43- 4. 5. Slide 2 of 37

Complete the following acid/base reactions: H2PO4- + H2O ⇌ A + B HPO42- + H2O ⇌ C + D HPO42- + H3O+ ⇌ E + F HPO42- + OH- ⇌ G + H A B C D E F G H 1. HPO42- OH- H2PO4- H2O 2. H3O+ PO4- H3PO4 3. PO43- 4. 5. Slide 3 of 37

Strong acid/strong base Consider the neutralization of a strong acid by a strong base and that of a weak acid by a weak base. Strong acid/strong base HCl (aq) + NaOH (aq) ⇌ H2O (l) + NaCl (aq) Ka SA/SB = ? Weak acid/weak base CH3COOH (aq) + NH3(aq) ⇌ H2O (l) + NH4CH3COO (aq) Ka WA/WB =? Predict the magnitude for the equilibrium constant for these two reactions: Ka SA/SB << 1; Ka SA/SB << 1 Ka SA/SB >> 1; Ka SA/SB >> 1 Ka SA/SB >> 1; Ka SA/SB << 1 Ka SA/SB << 1; Ka SA/SB >> 1 Ka SA/SB = 1; Ka SA/SB = 1 Slide 4 of 37

Strong acid/strong base Consider the neutralization of a strong acid by a strong base and that of a weak acid by a weak base. Strong acid/strong base HCl (aq) + NaOH (aq) ⇌ H2O (l) + NaCl (aq) Ka SA/SB = ? Weak acid/weak base CH3COOH (aq) + NH3(aq) ⇌ H2O (l) + NH4CH3COO (aq) Ka WA/WB =? Predict the magnitude for the equilibrium constant for these two reactions: Ka SA/SB << 1; Ka SA/SB << 1 Ka SA/SB >> 1; Ka SA/SB >> 1 Ka SA/SB >> 1; Ka SA/SB << 1 Ka SA/SB << 1; Ka SA/SB >> 1 Ka SA/SB = 1; Ka SA/SB = 1 Slide 5 of 37

CH3COOH (aq) + H2O (l) ⇌ H3O+ (aq) + CH3COO- (aq) Ke2 = ? Consider the following reactions of aqueous acetic acid, CH3COOH, CH3COOH (aq) + OH- (aq) ⇌ H2O (l) + CH3COO- (aq) Ke1 = ? CH3COOH (aq) + H2O (l) ⇌ H3O+ (aq) + CH3COO- (aq) Ke2 = ? Predict the magnitude for the equilibrium constant for each of these two reactions: Ke1 << 1; Ke2 << 1 Ke1 >> 1; Ke2 >> 1 Ke1 >> 1; Ke2 << 1 Ke1<< 1; Ke2 >> 1 Ke1 = 1; Ke2 = 1 Slide 6 of 37

CH3COOH (aq) + H2O (l) ⇌ H3O+ (aq) + CH3COO- (aq) Ke2 = ? Consider the following reactions of aqueous acetic acid, CH3COOH, CH3COOH (aq) + OH- (aq) ⇌ H2O (l) + CH3COO- (aq) Ke1 = ? CH3COOH (aq) + H2O (l) ⇌ H3O+ (aq) + CH3COO- (aq) Ke2 = ? Predict the magnitude for the equilibrium constant for these two reactions: Ke1 << 1; Ke2 << 1 Ke1 >> 1; Ke2 >> 1 Ke1 >> 1; Ke2 << 1 Ke1<< 1; Ke2 >> 1 Ke1 = 1; Ke2 = 1 Slide 7 of 37

The acid dissociation constant for hexanoic acid is 1. 41x10-5 The acid dissociation constant for hexanoic acid is 1.41x10-5. A buffer solution is prepared by mixing hexanoic acid and sodium hexanoate and is found to have a pH of 4.9. What is the ratio of the salt to acid concentration in this buffer solution? 1. 0 2. 0.5 3. 0.8 4. 1.0 5. 2.5 Slide 8 of 37

The acid dissociation constant for hexanoic acid is 1. 41x10-5 The acid dissociation constant for hexanoic acid is 1.41x10-5. A buffer solution is prepared by mixing hexanoic acid and sodium hexanoate and is found to have a pH of 4.9. What is the ratio of the salt to acid concentration in this buffer solution? 1. 0 2. 0.5 3. 0.8 4. 1.0 5. 2.5 Slide 9 of 37

10. 0 ml of 0. 200 molar NaOH is required to fully titrate a 30 10.0 ml of 0.200 molar NaOH is required to fully titrate a 30.0 mL sample of propanoic acid. What was the concentration of the acid sample? (no need to use a calculator). 1. 0.0333 M 2. 0.0500 M 3. 0.0667 M 4. 0.150 M 5. 0.200 M Slide 10 of 37

10. 0 ml of 0. 200 molar NaOH is required to fully titrate a 30 10.0 ml of 0.200 molar NaOH is required to fully titrate a 30.0 mL sample of propanoic acid. What was the concentration of the acid sample? (no need to use a calculator). 1. 0.0333 M 2. 0.0500 M 3. 0.0667 M 4. 0.150 M 5. 0.200 M Slide 11 of 37

15. 0 ml of an NaOH solution is required titrate a 30 15.0 ml of an NaOH solution is required titrate a 30.0 mL sample of oxalic which is known to be 0.0250 M. What was the concentration of the sodium hydroxide solution? (no need to use a calculator). 1. 0.0250 M 2. 0.0500 M 3. 0.100 M 4. 0.150 M 5. 0.250 M Slide 12 of 37

15. 0 ml of an NaOH solution is required titrate a 30 15.0 ml of an NaOH solution is required titrate a 30.0 mL sample of oxalic which is known to be 0.0250 M. What was the concentration of the sodium hydroxide solution? (no need to use a calculator). 1. 0.0250 M 2. 0.0500 M 3. 0.100 M 4. 0.150 M 5. 0.250 M Slide 13 of 37

What is the pH of a buffer solution composed of equimolar amounts of dimethylamine and dimethylammonium chloride? 1. 3.27 4. 10.73 2. 4.73 dimethylamine, Kb = 5.4x10-4 5. 14.00 3. 7.00 Slide 14 of 37

What is the pH of a buffer solution composed of equimolar amounts of dimethylamine and dimethylammonium chloride? 1. 3.27 4. 10.73 2. 4.73 dimethylamine, Kb = 5.4x10-4 5. 14.00 3. 7.00 Slide 15 of 37

A buffer solution containing equimolar amounts of the base, aniline, and the salt of its conjugate acid, aniline hydrochloride, will result in an acidic buffer solution. 1. True 2. False aniline Kb = 4.3x10-10 Slide 16 of 37

A buffer solution containing equimolar amounts of the base, aniline, and the salt of its conjugate acid, aniline hydrochloride, will result in an acidic buffer solution. 1. True 2. False aniline Kb = 4.3x10-10 Slide 17 of 37

Which of the following statements is incorrect? A buffer solution contains a weak acid or base and the salt of its conjugate base or acid, respectfully. 2. A buffer solution resists changes in pH upon addition of small amounts of acid or base. 3. The more concentrated the buffer solution is, the better its buffer capacity. 4. Water is a buffer solution with a pH of 7. 5. A buffer solution containing 0.10 M acid and conjugate base has the same pH as a solution containing 1.0 M of the same acid and conjugate base. Slide 18 of 37

Which of the following statements is incorrect? A buffer solution contains a weak acid or base and the salt of its conjugate base or acid, respectfully. 2. A buffer solution resists changes in pH upon addition of small amounts of acid or base. 3. The more concentrated the buffer solution is, the better its buffer capacity. 4. Water is a buffer solution with a pH of 7. 5. A buffer solution containing 0.10 M acid and conjugate base has the same pH as a solution containing 1.0 M of the same acid and conjugate base. Slide 19 of 37

4. will contain undissolved sodium malonate Malonic acid is a diprotic acid with the acid dissociation constants given to the right. A solution which contains sodium malonate NaC3H3O4 malonic acid 1. is basic Ka,1 = 1.5x10-3 2. is acidic Ka,2 = 2.0x10-6 3. is neutral 4. will contain undissolved sodium malonate 5. None of the above answers is correct. Slide 20 of 37

4. will contain undissolved sodium malonate Malonic acid is a diprotic acid with the acid dissociation constants given to the right. A solution which contains sodium malonate NaC3H3O4 malonic acid 1. is basic Ka,1 = 1.5x10-3 2. is acidic Ka,2 = 2.0x10-6 3. is neutral 4. will contain undissolved sodium malonate 5. None of the above answers is correct. Slide 21 of 37

4. does not register on the pH scale. Ascorbic acid is a diprotic acid (acidic groups circled). A solution which contains the mono-sodium salt of ascorbic acid, sodium ascorbate, ascorbic acid Ka,1 = 8.0x10-5 Ka,2 = 1.6x10-12 1. is basic 2. is acidic 3. is neutral 4. does not register on the pH scale. 5. None of the above answers is correct. Slide 22 of 37

4. does not register on the pH scale. Ascorbic acid is a diprotic acid (acidic groups circled). A solution which contains the mono-sodium salt of ascorbic acid, sodium ascorbate, ascorbic acid Ka,1 = 8.0x10-5 Ka,2 = 1.6x10-12 1. is basic 2. is acidic 3. is neutral 4. does not register on the pH scale. 5. None of the above answers is correct. Slide 23 of 37

A technician collects a sample of rainwater to test the pH A technician collects a sample of rainwater to test the pH. Her portable pH meter is reading low battery. Litmus paper turns red indicating that the sample is acidic. As well, methyl red was found to turn red and both bromphenol blue and thymol blue were found to turn yellow. What is the best pH range of the rainwater sample as determined by these experimental results? 1. pH < 2 2. 2 < ph < 3 3. 2.5< ph < 3.5 4. 3.5 < ph < 4.5 5. 4 < ph < 5 Slide 24 of 37

A technician collects a sample of rainwater to test the pH A technician collects a sample of rainwater to test the pH. Her portable pH meter is reading low battery. Litmus paper turns red indicating that the sample is acidic. As well, methyl red was found to turn red and both bromphenol blue and thymol blue were found to turn yellow. What is the best pH range of the rainwater sample as determined by these experimental results? 1. pH < 2 2. 2 < ph < 3 3. 2.5< ph < 3.5 4. 3.5 < ph < 4.5 5. 4 < ph < 5 Slide 25 of 37

The titration curve to the right best represents the titration of : equivalence point 1. a weak base with a strong acid. 2. a weak acid with a strong base. pH 3. a strong acid with a strong base. 4. a strong base with a strong acid. volume of titrant / ml Slide 26 of 37

The titration curve to the right best represents the titration of: equivalence point 1. a weak base with a strong acid. 2. a weak acid with a strong base. pH 3. a strong acid with a strong base. 4. a strong base with a strong acid. volume of titrant / ml Slide 27 of 37

Which of the following titration curves best represents the titration of 15.0 mL of 0.010 M NaOH with 0.0060 M HCl? volume of titrant / ml 10 20 30 40 50 pH 7 14 volume of titrant / ml 10 20 30 40 50 pH 7 14 volume of titrant / ml 10 20 30 40 50 pH 7 14 1. 2. 3. Slide 28 of 37

Which of the following titration curves best represents the titration of 15.0 mL of 0.010 M NaOH with 0.0060 M HCl? volume of titrant / ml 10 20 30 40 50 pH 7 14 volume of titrant / ml 10 20 30 40 50 pH 7 14 volume of titrant / ml 10 20 30 40 50 pH 7 14 1. 2. 3. Slide 29 of 37

In the titration of a weak acid with a strong base methyl red was used as the indicator. Which of the points on the titration curve to the right represents the equivalence point in the titration? 5. 4. 3. 2. 1. Slide 30 of 37

In the titration of a weak acid with a strong base methyl red was used as the indicator. Which of the points on the titration curve to the right represents the equivalence point in the titration? 5. 4. 3. 2. 1. Slide 31 of 37

In the titration of a weak acid with a strong base methyl red was used as the indicator. Which of the points on the titration curve to the right represents the endpoint in the titration? 5. 4. 3. 2. 1. Slide 32 of 37

In the titration of a weak acid with a strong base methyl red was used as the indicator. Which of the points on the titration curve to the right represents the endpoint in the titration? 5. 4. 3. 2. 1. Slide 33 of 37

1. depends on the indicator used When titrating a solution containing a weak acid such as acetic acid, the pH at the endpoint of the titration: 1. depends on the indicator used 2. is below 7.0 3. is above 7.0 Slide 34 of 37

1. depends on the indicator used When titrating a solution containing a weak acid such as acetic acid, the pH at the endpoint of the titration: 1. depends on the indicator used 2. is below 7.0 3. is above 7.0 Slide 35 of 37

Based on the titration curve to the right, the compound being titrated is most likely: 1. H2Se: pKa,1=3.89, pKa,2=11.0 2. H2SeO4: strong acid, pKa,2=3.66 3. H2SeO3: pKa,1=2.65, pKa,2= 8.25 4. Citric acid: pKa,1=3.75, pKa,2= 4.77 5. Valine: pKa,1=2.29, pKa,2= 9.74 Slide 36 of 37

Based on the titration curve to the right, the compound being titrated is most likely: 1. H2Se: pKa,1=3.89, pKa,2=11.0 2. H2SeO4: strong acid, pKa,2=3.66 3. H2SeO3: pKa,1=2.65, pKa,2= 8.25 4. Citric acid: pKa,1=3.75, pKa,2= 4.77 5. Valine: pKa,1=2.29, pKa,2= 9.74 Slide 37 of 37