Practice Problems Module 10: Acid, Base, Solution Equilibrium

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1 Practice Problems Module 10: Acid, Base, Solution Equilibrium The headings on these problems correspond to the headings on your content pages. You should work on these throughout the unit. Be sure to show all your work, otherwise you won t know where you went wrong if you made a mistake. Many times it is easier to write out your work using pen and paper, so you may choose to scan your work if you like. Just make sure that it is clear enough for me to see! Scanned work should be saved as one pdf file. Multiple files may be too large for the dropbox. If you type your answers, use a different color font, highlight, textbox, etc. to make the work easier to see. Place the completed document into the Module 10: Acid, Base, Solution Equilibrium Practice Problems dropbox according to your schedule. Acids and Bases, Amphoteric, Acid Strength, Base Strength 1. Write the formula for the conjugate base of each of the following: a. NH 2 OH b. HSO 3 2. Identify the conjugate acid-base pairs in the following reactions: a. HSO SO 3 HSO SO 4 b. S 2 + H 2 O HS + OH 3. Choose the stronger acid: (a) HBr or HCl; (b) H 2 O or HF; (c) H 2 S or HBr. Give your reasons. 4. Choose the stronger acid: (a) HOCl or HClO 2 ; (b) H 2 SeO 4 or H 2 SeO 3. Give your reasons. Auto-Ionization of Water, The ph Concept 5. Write the chemical equation for the autoionization of water and the equilibrium law for Kw. 6. How are acidic,basic,and neutral solutions in water de fined (a) in term terms of ph? 7. At 25 C, how are the ph and poh of a solution related to each other? 8. Calculate the OH concentration in each of the following solutions in which the H + concentrations are a M b M 9. Calculate the ph of each solution in the previous problem. 10. A soft drink was put on the market with [H + ] = mol L 1. What is its ph? 11. Calculate the molar concentrations of H + and OH in solutions that have the following poh values: a b c What is the concentration of H + in M HClO 4? What is the ph of the solution? What is the OH concentration in the solution?

2 13. A sodium hydroxide solution is prepared by dissolving 6.0 g NaOH in 1.00 L of solution. What is the molar concentration of OH in the solution? What is the poh and the ph of the solution? What is the hydrogen ion concentration in the solution? 14. It was found that ml of an HNO 3 solution are needed to react completely with 300 ml of a LiOH solution that has a ph of What is the molarity of the HNO 3 solution? Weak Acids and Bases, pka and pkb 15. Write the chemical equation for the ionization of each of the following weak acids in water. (Some are polyprotic acids; for these write only the equation for the first step in the ionization.) a. HNO 2 b. H 3 PO For each of the acids in above, write the appropriate K a expression. 17. Write the chemical equation for the ionization of each of the following weak bases in water: a. (CH 3 ) 3 N b. AsO For each of the bases in the previous question, write the appropriate K b expression. 19. The barbiturate ion, C 4 H 3 N 2 O 3, has K b = What is K a for barbituric acid? 20. Iodic acid, HIO 3, has a pk a of (a) What is the formula and the K b of its conjugate base? (b) Is its conjugate base a stronger or a weaker base than the acetate ion? ph of strong Acids and Bases, ph of Weak Acids and Bases, Percent Ionization, Calculating ka and kb 21. What are the concentrations of all the solute species in M lactic acid, HC 3 H 5 O 2? What is the ph of the solution? This acid has K a = Pyridine, C 6 H 5 N, is a bad-smelling liquid that is a weak base in water. Its pk b is What is the ph of a 0.20 M aqueous solution of this compound? 23. If a weak base is 0.030% ionized in M solution, what is the ph of the solution? 24. Ethylamine, CH 3 CH 2 NH 2, has a strong, pungent odor similar to that of ammonia. Like ammonia, it is a Brønsted base. A 0.10 M solution has a ph of Calculate the K b and pk b for ethylamine. What is the percentage ionization of ethylamine in this solution? ph of Salt Solutions, Calculating the ph of Salt Solutions 25. Consider the following compounds and suppose that 0.5 M solutions are prepared of each: NaI, KF, (NH4)2SO4, KCN, KC2H3O2, CsNO3, and KBr. Write the formulas of those that have solutions that are (a) acidic, (b) basic, and (c) neutral. 26. Calculate the ph of 0.10 M hydrazinium chloride, N 2 H 5 Cl. 27. Calculate the ph of 0.40 M KNO 2. What is the concentration of HNO 2 in the solution? 28. Calculate the ph of 0.15 M CH 3 NH 3 Cl. For methylamine, CH 3 NH 2, K b = Calculate the number of grams of NH 4 Br that have to be dissolved in 1.00 L of water at 25 C to have a solution with a ph of 5.16.

3 Buffers, ph of a Buffered Solution, How Buffers Work, Preparing a Buffer of a Given ph, Buffer Capacity 30. Write ionic equations that illustrate how each pair of compounds can serve as a buffer pair. (a) H 2 CO 3 and NaHCO 3 (the carbonate buffer in blood) (b) NaH 2 PO 4 and Na 2 HPO 4 (the phosphate buffer inside body cells) (c) NH 4 Cl and NH Which buffer would be better able to hold a steady ph on the addition of strong acid, buffer 1 or buffer 2? Explain. Buffer 1 is a solution containing 0.10 M NH 4 Cl and 1 M NH 3. Buffer 2 is a solution containing 1 M NH 4 Cl and 0.10 M NH Bicarbonate ion is able to act as a buffer all by itself. Write chemical equations that show how this ion reacts with (a) H + and (b) OH What is the ph of a solution that contains 0.15 M HC 2 H 3 O 2 and 0.25 M C 2 H 3 O 2? 34. How many grams of sodium formate, NaCHO 2, would have to be dissolved in 1.0 L of 0.12 M formic acid (pk a 3.74) to make the solution a buffer for ph 3.80? Titration, Strong Acid/Strong Base Titration, Titration Curves, Indicators, Titration Calculations Strong Acid/Strong Base 35. Describe each of the following: (a) buret, (b) titration, (c) titrant, and (d) end point. 36. What is the function of an indicator in a titration? What color is phenolphthalein in (a) an acidic solution and (b) a basic solution? 37. When 50 ml of 0.10M formic acid, HCHO 2, is titrated with 0.10M sodium hydroxide, what is the ph at the equivalence point? (Be sure to take into account the change in volume during the titration.) Select a good indicator for this titration from Table What is the ph of a solution prepared by mixing exactly 30.0 ml of M HC 2 H 3 O 2 with 15.0 ml of M KOH? 39. What can be inferred about the general titration represented by the titration curve below? a. A strong acid is titrated. b. A strong base is titrated. c. A weak acid is titrated. d. A weak base is titrated.

4 40. What can be inferred from the figure below? a. A weak base is titrated. b. The titrant is a base. c. The titrant is an acid. d. The ph of the equivalence point is less than Consider the titration curve below: a. If this curve is of a strong acid titrated with a strong base. Which point represents the equivalence point? b. Consider the titration curve below, that shows a strong acid titrated with a strong base. If the acid were weak, at which point would the solution be buffered. c. If the titration were repeated using a stronger acid (and all other variables remained the same), where would the curve intersect the y axis? At A Below A Above A It would not intersect the y axis None of the above Polyprotic Acids, Salt Solutions of Polyprotic Acids, Titrations of Polyprotic Acids 42. What is the ph of a 0.50 M solution of arsenic acid, H 3AsO 4? In this solution, what are the concentrations of H 2 AsO 4 and HAsO 4 2? Solubility Equilibria, Ion Product and Ksp, Determining Ksp From Solubility Data

5 43. Write the K sp expressions for each of the following compounds: a. AgI b. Ag 3 PO A student found that a maximum of g AgC 2 H 3 O 2 is able to dissolve in 100 ml of water. What is the molar solubility and the K sp for this salt? # moles AgC 2 H 3 O 2 = ( g AgC 2 H 3 O 2 ) 1 mole AgC 2 H 3O g AgC 2 H 3 O 2 = moles AgC 2 H 3 O A student prepared a saturated solution of CaCrO 4 and found that when 156 ml of the solution was evaporated, g of CaCrO 4 was left behind. What is the value of K sp for this salt? 46. The molar solubility of Ba 3 (PO 4 ) 2 in water at 25 C is mol L 1. What is the value of K sp for this salt? 47. What is the molar solubility of Ag 2 CrO 4 in water? 48. Calculate the molar solubility of PbI 2 in water. Common Ion Effect, Precipitation 49. Copper(I) chloride has K sp = Calculate the molar solubility of CuCl in (a) pure water, (b) M HCl solution, (c) M HCl solution, and (d) M CaCl 2 solution.