Chemistry 400 Homework #3, Chapter 16: Acid-Base Equilibria I. Multiple Choice (for those with an asterisk, you must show work) These multiple choice (MC) are not "Google-proof", but they were so good that I had to use them. Still, make sure you learn the material in these MC questions! 1) Proton acceptor is an abbreviated definition of: A) Br nsted-lowry base B) Br nsted-lowry acid C) Lewis base D) Lewis acid E) Arrhenius acid 2) In the equilibrium system described by: PO 3-4 (aq) + H2 O(l) HPO 2-4 (aq) + OH -, Br nsted-lowry theory would designate: A) PO4 3- and H2O as the bases B) H2O and OH- as a conjugate pair C) HPO4 2- and OH- as the acids D) HPO4 2- and H2O as a conjugate pair E) PO4 3- as amphiprotic 3) Choose the strongest acid. A) HF B) H2CO3 C) HCN D) HC2H3O2 E) HClO4 4) Which of the following are Br nsted-lowry acids? I) CH3COOH II) [Cu(H2O)4]2+ III) H2O IV) CH3NH2 V) H3O+ A) I), II) and III) B) II), III), and IV) C) I), II), III) and IV) D) I), II), III), and V) E) II), III) and V) 5) Which of the following is the strongest base? A) Cl- B) ClO4 - C) F- D) NO3 - E) H2O 6) poh = 3.14 is equivalent to: A) ph = 11. B) [H+] = 1.4 10-10 M C) [OH-] = 7.2 10-4 M D) [H+} = 7.0 10-4 M E) [OH-] = 3.14 10-7 M 1
*7) 0.272 g of a monoprotic acid (Mw = 189 g/mol) is dissolved in water to produce 25.0 ml of a solution with ph = 4.93. Determine the ionization constant of the acid. A) 4.1 10-8 B) 1.4 10-10 C) 2.1 10-4 D) 2.8 10-7 E) 2.4 10-9 8) Which of the following is a logical inference from the fact that a 0.10 molar solution of potassium acetate, KC2H3O2, is less alkaline than a 0.10 molar solution of potassium cyanide, KCN? A) Hydrocyanic acid is a weaker acid than acetic acid. B) Cyanides are less soluble than acetates. C) Hydrocyanic acid is less soluble in water than acetic acid. D) Acetic acid is a weaker acid than hydrocyanic acid. E) 0.10 M potassium acetate is more concentrated than 0.10 M potassium cyanide. 9) Which of the following statements concerning aqueous solutions of salts is FALSE? A) For any salt of a strong acid and a strong base, the ph will be about 7. B) For any salt of a strong acid and a weak base, the ph will be <7. C) For any salt of a weak acid and a strong base, the ph will be >7. D) For any salt of a weak acid and a weak base, the ph will be about 7. *10) If one mole of Ba(OH)2 is added to enough water to make 10 liters of solution, the ph of the resulting solution is. A) 13.3 B) 1.0 C) 0.7 D) 13.0 E) 12.5 11) For the following compound, predict whether the solution is acidic, basic, or neutral and why: Na2CO3. A) acidic because Na+ is a strong acid B) basic because CO3 2- is a weak base C) neutral because there is no hydrolysis D) basic because CO3 2- is a strong base E) acidic because Na+ is a weak acid *12) A certain acid, HA, has a Ka given by: HA + H2O H3O+ + A- Ka = 6.80 10-6 What is the ph of a 0.247 M solution of the acid's potassium salt, KA? A- + H2O OH- + HA A) 4.72 B) 9.28 C) 4.11 D) 9.89 E) 9.44 13) What is the indication of the relative acid strengths of the following acids? CH3CH2CHClCOOH CH3CHClCH2COOH CH2ClCH2CH2COOH A) CH3CHClCH2COOH > CH2ClCH2CH2COOH > CH3CH2CHClCOOH B) CH2ClCH2CH2COOH > CH3CH2CHClCOOH > CH3CHClCH2COOH C) CH2ClCH2CH2COOH > CH3CHClCH2COOH > CH3CH2CHClCOOH D) CH3CH2CHClCOOH > CH3CHClCH2COOH > CH2ClCH2CH2COOH E) CH3CH2CHClCOOH > CH2ClCH2CH2COOH > CH3CHClCH2COOH 2
14) Which of the following substances is never a Brønsted-Lowry acid in an aqueous solution? A) sodium dihydrogen phosphate, NaH 2 PO 4 (s) B) sodium acetate, NaCH 3 CO 2 (s) C) ammonium nitrate, NH 4 NO 3 (s) D) hydrogen bromide, HCl(g) E) sodium bicarbonate, NaHCO 3 (s) 15) The autoionization of pure water, as represented by the equation below, is known to be endothermic. Which of the following correctly states what occurs as the temperature of pure water is raised? H 2 O(l) + H 2 O(l) H 3 O + (aq) + OH (aq) A) K w decreases, and the hydronium ion concentration decreases. B) K w decreases, and the hydronium ion concentration increases. C) K w and the hydronium ion concentration do not change. D) K w increases, and the hydronium ion concentration decreases. E) K w increases, and the hydronium ion concentration increases. 16) Which of the following expressions is not equivalent to ph? A) log [H + (aq)] B) C) 14.0 poh D) E) log K w *17) Given that K a for HOCl is 3.5 10 8 and the K a for HF is 7.2 10 4 (both at 25 C), which of the following is true concerning K c for Consider the reaction HOCl + F HF + OCl at 25 C? A) K is greater than 1. B) K is less than 1. C) K is equal to 1. D) Cannot be determined with the above information. E) None of these (A-D). 18) HA and HB are both weak acids in water, and HA is a stronger acid than HB. Which of the following statements is correct? A) A is a stronger base than B, which is a stronger base than H 2 O, which is a stronger base than Cl. B) B is a stronger base than A, which is a stronger base than H 2 O, which is a stronger base than Cl. C) B is a stronger base than A, which is a stronger base than Cl, which is a stronger base than H 2 O. D) Cl is a stronger base than A, which is a stronger base than B, which is a stronger base than H 2 O. E) None of these (A-D) is correct. 19) True or false: The species Cl is not a good base in aqueous solution. A) True. This is because Cl is the conjugate base of a weak acid. B) False. The species Cl is a good base in aqueous solution because it is the conjugate base of a strong acid. C) True. This is because Cl is a good proton donor. D) False. The species Cl is a good base in aqueous solution because of its high electronegativity. E) True. This is because water has a stronger attraction for protons than does Cl. 3
20) At 65 C, the ion-product constant of water, K w, is 1.20 10 13. The ph of pure water at 65 C is: A) 7.000 B) 6.560 C) 5.880 D) 6.460 E) none of these 21) You have 100.0 ml of a solution of hydrochloric acid that has a ph of 3.00. You add 100.0 ml of water to this solution. What is the resulting ph of the solution? A) The ph = 5.00 (the average of 3.00 and 7.00). B) The ph = 10.00 (3.00 + 7.00 = 10.00). C) The ph = 3.00 (water is neutral and does not affect the ph). D) None of the above is correct, but the ph must be greater than 3.00. E) None of the above is correct, but the ph must be less than 3.00. II. Short answer (Google-proof, Chegg-proof, made these up myself) 1. Write the formula for the conjugate base of each acid: A. HCl B. H 2 SO 3 C. HCOOH 2. H 2 O is amphoteric. A. Write a reaction in which H 2 O acts as an acid. B. Write a reaction in which H 2 O acts as a base. 3. Rank the following solutions in order from highest to lowest ph: 0.10 M HF, 0.10 M HClO 2, 0.10 M NaOH, 0.10 M HNO 3, 0.10 M NH 3, 4. Complete the table: ph [H + ] (mol/l) [OH ] (mol/l) Acid/Base Sol'n? 7.20 4.32 2.9 x 10-12 5.4 10 9 6.7 x 10-9 8.8 10 4 4
5. For each of the following solutions, calculate the [H 3 O + ], [OH - ], and the ph. A. 0.15 M HCl B. 0.15 M CH 3 COOH C. 257 ml of HCl(g) at 25 C and 745 mm Hg dissolved in 750.0 ml of solution. D. 0.100 M benzoic acid 6. A 0.150 M solution of a weak acid has a ph of 2.65. A. Calculate the acid ionization constant K a for the acid. B. What is the percent ionization of the acid? 5
7. For acetic acid, calculate and make a plot in Excel of the percent ionizations of acetic acid as a function of the acid's initial concentration. Initial Concentration 0.0001 Percent Ionization 0.001 0.01 0.05 0.1 Based on your plot, what do you think happens to the percent ionization as the initial concentration goes to zero? If you are unsure, solve a few more at lower concentrations until you are sure. 8. Write a K b reaction for: A. CO 3 2- (aq) B. C 6 H 5 NH 2 (aq) 6
9. What is the ph of a 0.23 M solution of CO 3 2- (aq)? 10. Arrange the solutions in order of increasing acidity: NaCl, NH 4 Cl, KCN, NaOH, NaCH 3 COO, NaC 3 H 5 O 3, Nicotine, C 2 H 5 NH 3 Cl 11. What is the ph of each of the following solutions? A. 0.10 M NH 4 Cl B. 0.20 M CH 3 NH 3 I 7
12. Calculate the concentration of all species (H 3 PO 4, H 2 PO 4-, HPO 4 2-, PO 4 3- ) and the ph of a 0.200 M solution of H 3 PO 4. 13. What is the trend in acid strength for the following acids: HOCl HOBr HOI Why? 14. What is the trend in acid strength for the following acids: HClO 4 HClO 3 HClO 2 HClO Why? 15. What is the ph of a solution with two acids: 0.045 M HCl and 0.175 M CH 3 COOH? 8
16. Tricky question that looks like a normal question: What is the ph when 15.0 g of NH 4 CH 3 COO are dissolved in 1.00 L of water? Assume it all dissolves. 17. Extension question of things we've already done in class but that you've never seen before: In very cold locations, water cannot be used as the solvent, so liquid ammonia can be used. The autoionization constant of ammonia is K am = 1 10-30 at -50 C. A. Write the autoionization reaction or NH 3. B. is the conjugate base of NH 3 and is the conjugate acid of NH 3. C. At -50 C, what would be the pnh 4 of a neutral solution (in analogy to ph)? 9