Chapter 16 Additional Practice Problems

Transcription

1 Chapter 16 Additional Practice Problems 1. Although pure NaOH and CaO have very different properties, their aqueous solutions possess many common properties. List some general properties of these solutions and explain their common behavior in terms of the species present. 2. (a) Write a chemical equation that illustrates the autoionization of water. (b) Write the expression for the ion-product constant for water, K w. Why is [H 2 O] omitted from this expression? (c) A solution is described as basic. What is meant by this statement? 3. Determine whether each of the following solutions is acidic, basic, or neutral: (a) [H + ] = [OH - ]; (b) 4.0 x 10-5 M OH - ; (c) 6.5 x 10-7 M H + ; (d)[h + ] = M; (e) [OH - ] = M. 4. Calculate the concentration of H + (aq) in each of the following solutions: (a) [OH - ] = 4.5 x M; (b) [OH - ] = 1.50 M; (c) A solution in which [H + ] is five times greater than [OH - ]. 5. (a) What is the difference between the Arrhenius and the Bronsted-Lowry definitions of a base? (b) When ammonia is dissolved in water, it behaves both as an Arrhenius base and a Bronsted-Lowry base. Explain. 6. Give the conjugate acid of the following Bronsted-Lowry bases: (a) NH 3 ; (b)clo 3 - ; (c) PO 4 3- ; (d) HCO 3 - ; (e) H 2 S. 7. Identify the acid, base, conjugate acid, and the conjugate base in each of the following equilibria: (a) HC 2 O 4 - (aq) + CO 3 2- (aq) C 2 O 4 2- (aq) + HCO 3 - (aq) (b) PH 4 + (aq) + H 2 O (l) PH 3 (aq) + H 3 O + (aq) (c)nh 4 + (aq) + CN - (aq) NH 3 (aq) + HCN (aq) 8. Which of the following would you expect to be the stronger Bronsted-Lowry base: (a) CN - or Cl - ; (b) NO 3 - or CO 3 2-? Briefly explain your choice. 9. (a) Write an equation for the reaction in which H 2 PO 4 - (aq) acts as a base in H 2 O (l); (b) Write an equation for the reaction in which H 2 PO 4 - (aq) acts as an acid in H 2 O (l); (c) What is the conjugate acid of H 2 PO 4 -? What is its conjugate base? 10. Indicate whether the following are acidic, basic, or neutral: (a) ph = 7.00;(b)pH = -0.57; (c) poh = 12.31; (d) poh = Calculate the ph of each of the following: (a) 4.2 x 10-5 M H + ; (b) H + = 1.20M; (c)poh = 11.21; (d) 0.92 M OH Calculate the H + and OH - for each of the following: (a) ph = 6.21; (b) poh = 1.00; (c) ph = 9.88; (d) poh = Deuterium oxide (D 2 O, where D = deuterium, the hydrogen-2 nuclide) has an ion-product constant, K w, of 8.9 x at 20 0 C. Calculate D +, OD -, pd, and pod for pure (neutral) D 2 O at this temperature.

2 14. Consider two solutions, solution A and solution B. H + in solution A is 500 times greater than that in solution B. What is the difference in the ph values of the two solutions? 15. (a) What is a strong base? (b) A solution is labeled M Sr(OH) 2. What is OH - for the solution? (c) Is the following statement true or false? Because Mg(OH) 2 is not very soluble, it cannot be a strong base. Explain. 16. Calculate the ph of each of the following strong acid solutions: (a) 1.8 x 10-4 M HBr; (b) 1.02 g of HNO 3 in 250 ml of solution; (c) 2.00 ml of M HClO 4 diluted to 50.0 ml; (d) a solution formed by mixing 10.0 ml of M HBr with 20.0 ml of 2.50 x 10-3 M HCl. 17. Calculate the OH - and ph for (a) 3.5 x 10-4 M Sr(OH) 2 ; (b) 1.50 g of LiOH in 250 ml of solution; (c) 1.00 ml of M NaOH diluted to 2.0 L; (d) a solution formed by adding 5.00 ml of M KOH to 15.0 ml of 3.5 x 10-3 M Ca(OH) Using the table at the end of your text and your knowledge of strong acids, select the strongest and weakest acid in the following list: HF, HCN, HC 7 H 5 O 2, HBr. 19. A M solution of KHCrO 4 has a ph of Calculate K a for HCrO Determine the ph of each of the following (K a and K b values are given in appendix D): (a) M hypochlorous acid, (b) M Phenol, (c) M hydroxylamine. 21.Calculate [OH - ] and ph for a M solution of dimethylamine, (CH 3 ) 2 NH. The value of K b is given in Appendix D. 22.Calculate the percent ionization of HCrO 4 - in solutions of each of the following concentrations (K a given in Appendix D): (a) 0.;0250 M; (b) M; (c) M. 23.A M solution of bromoacetic acid, CH 2 BrCOOH, is 13.2 percent ionized. Using this information, calculation [CH 2 BrCOO - ], [H + ], [CH 2 BrCOOH], and K a for bromoacetic acid. 24.Write the balanced net ionic equation for the reaction of each of the following bases with water. Also write the base-dissociation-constant expression for each substance (a) hydrazine, H 2 NNH 2 (b) methylamine, CH 3 NH 2 ; (c) benzoate ion, (C 6 H 5 CO (a) Write a chemical equation that shows the reaction of the phenolate ion, C 6 H 5 O -, as a base with water. (b)although the acid-dissociation for phenol, C 6 H 5 O H, is listed in Appendix D, the basedissociation constant K b for the phenolate ion is not. Explain why it is not necessary to list both K a for phenol and K b for phenolate ion. 26. Using the values of K b from appendix D, calculate K a for each of the following species: (a) dimethylammonium ion, (CH 3 ) 2 NH + 2, (b) hydrazimium ion H 3 NNH + 2, ( c ) pyridimium ion, C 5 H 5 NH +, (d) hydroxylammonium ion, HONH Calculate OH - and ph for each of the following solutions: (a) 0.10 M NaF, (b) 0.10 M Na 2 S, (c) a mixture that M in NaC 2 H 3 O 2 and M in Ba(C 2 H 3 O 2 ) 2.

3 28. Indicate whether each of the following substances would form an acidic, basic, or neutral solution in water: (a) NaHC 2 O 4 -, (b) CsI, (c) Al(NO 3 ) 3, (d) NH 4 CN. 29. (a) How does the strength of an acid vary with the polarity and strength of the H-X bond? (b) How does the acidity of the hydride of an element vary as a function of the electronegativity of the element? How does this relate to the position of the element in the periodic table? 30. Based on their composition and structures and on conjugate acid-base relationships, select the member of each of the following pairs that is the stronger base: (a) BrO - or BrO 2 - ; BrO - or ClO - ; (c) HPO 4 2- or H 2 PO Indicate whether each of the following statements is true or false. For those that are false, correct the statement so that it is true: (a) Acid strength in a series H n X increases with increasing size of X. (b) For acids of the same structure but differing electronegativity of the central atom, acid strength decreases with increasing electronegativity of the central atom. (c) The strongest acid of all is HF because fluorine is the most electronegative element. 32. For each of the following descriptive statements, provide an interpretation in terms of the Bronsted- Lowry theory, the Lewis theory, or both, as appropriate. (a) Hydrogen bromide dissolves in water to form an acidic solution. (b) Sodium hydride, NaH, reacts with water to forma basic solution. (c) Pyridine reacts with sulfur dioxide in a dry organic solvent to form pyridine-so 2. (d) Sulfur dioxide, SO 2, dissolves in water to form an acidic solution. 33. Identify the Lewis acid and the Lewis base in each of the following reactions: (a) HNO 2 (aq) + OH - (aq) NO 2 - (aq) + H 2 ) (l) (a) FeBr 3 (s) + Br - (aq) FeBr 4 - (aq) (b) Zn 2+ (aq) + 4 NH 3 (aq) Zn(NH 3 ) 4 2+ (aq) (c) SO 2 (g) + H 2 O (l) H 2 SO 3 (aq) 34. Which member of each of the following pairs would you expect to be the stronger Lewis acid: (a) BH 4 - or BH 3 ; (b) S 8 or SO 3 - ; (c) NaH or HBr; (d) Mo 4+ or Zn 2+? 35.Calculate the[h + ] for each of the following solutions: (a) urine, ph = 6.1; (b) lemon juice, ph = 2.1; (c) gastric juice, ph = 1.4; (d) household ammonia, ph = Indicate in each case whether the solution is acidic, basic, or neutral. 36. Arrange the following bases in order of their tendency to combine with protons, putting the strongest base first: NH 3 ; H 2 O ; OH - ; C 2 H 3 O 2 - ; Br -.

4 Answers 1.Both dissolve in H 2 O: NaOH completely dissociates and CaO (s) + H 2 O (l) Ca 2+ (aq) + 2 OH - (aq). Both solutions contain OH -, taste bitter, turn litmus blue (are basic, conduct electricity and neutralize acids. 2. a) H 2 O (l) H + (aq) + OH - (aq) b) K w = H + OH - Water is a pure liquid. c) solution contains more OH - than H + 3. a) neutral; b) ph=9.6 (basic); c) ph=6.2 (acidic); d) ph=9.3 (basic); e) ph=7 (neutral 4. a) 2.2 x 10-4 M; b) 6.7 x M; c) OH - = 4.5 x 10-8 M and H + = 2.3 x 10-7 M 5. a) Arrhenius acid: H + in water, base is OH - in water Bronsted-Lowry: acid is an H + donor, base is H + acceptor b) NH 3 (g) + H 2 O (l) NH 4 + (aq) + OH - (aq) NH 3 in water produces OH - (Arrheius); NH 3 accepts H + from Water base (Bronsted-Lowry) 6. a) NH 4 + ; b) HClO 3 ; c) HPO 4 2- ; d) H 2 CO 3 ; e) H 3 S - 7. Acid Base Con Acid Con Base - a) HC 2 O 4 2- CO 3 - HCO 3 2- C 2 O 4 + b) PH 4 H 2 O H 3 O + PH 3 + c) NH 4 CN - HCN nh 3 8. a) CN -, HCl completely dissociates in water and Cl - has no tendency to accept H + (aq) b) CO 3 2-, same as (a) 9. a) H 2 PO 4 - (aq) + H 2 O (l) H 3 PO 4 (aq) + OH - (aq) b) H 2 PO 4 - (aq) + H 2 O (l) HPO 4 2- (aq) + H 3 O + (aq) c) H 3 PO 4 is the C.A. of H 2 PO 4 - ; HPO 4 2- is the C.B. of H 2 PO a) N; b) A; c) A; d) B 11. a) 4.4; b) 0.079; c) 2.79; d) a) H + = 6.17 x 10-7 M; OH - = 1.62 x 10-8 M b) H + = 1.00 x 10-3 M; OH - = 1.00 x M c) H + = 1.32 x M; OH - = 7.59 x 10-5 M d) H + = 3.16 x 10-8 M; OH - = 3.16 x 10-7 M 13. D + = OD - = 3.0 x 10-8 M; pd = pod = The ph of solution A is 2.70 ph units lower than the ph of solution B. 15.a) strong base completely dissociates in water b) OH - = M c) relatively few Mg(OH) 2 units dissociate in water weak base. 16.a) 3.74; b) 1.19; c) 1.699; d) a) OH - = 7.0 x 10-4 M; ph = b) OH - = M; ph = c) OH - = 4.75 x 10-5 M; ph = 9.68

5 d) OH - = 7.88 x 10-3 M; ph = HBr strongest; HCN weakest x a) 4.4; b) 6.02; c) OH - = 8.05 x 10-4 M; ph = a) 0.11%; b) 0.19%; c) 0.39% 23. CH 2 BrCOO - = M; H + = M; CH 2 BrCOOH =0.0868M K a = 2.0 x a) H 2 NNH 2 (aq) + H 2 O (l) H 2 NNH 3 + (aq) + OH - (aq) b) CH 3 NH 2 (aq) + H 2 O (l) CH 3 NH 3 + (aq) + OH - (aq) c) C 6 H 5 CO 2 - (aq) + H 2 O (aq) HC 6 H 5 CO 2 (aq) + OH - (aq) 25. a) C 6 H 5 O - (aq) + H 2 O + (l) C 6 H 6 O (aq) + OH - (aq) b) K a K b = K w ; K b = 7.7 x a) 1.9 x ; b) 7.7 x 10-9 ; c) 5.9 x 10-6 ; d) 9.1 x a) OH - = 1.2 x 10-6 M; ph = 8.08 b) OH - = M; ph = c) OH - = 1.0 x 10-5 M; ph = a) A; b) N; c) A; d) B 29. a) Acid strength increases as the polarity of the X-H bond increases, and decreases as the strength of the X-H bond decreases b) If X is more electronegative than H, as the electronegativity of X increases, the X-H bond becomes more polar and strength of the acid increases. This trend holds true as electronegativity increases across a row. As it decreases down a group, acid strength increases because the strength of the H-X bond decreases even though the H-X bond becomes less polar. 30. a) BrO -, more nonprotonated O atoms in HbrO 2 b) BrO -, HClO is stronger acid due to more electronegative central atom, so BrO - is the stronger base c) HPO 4 2-, larger negative charge, greater attraction for H a) true b) false, Acid strength increases as the electronegativity of the central atom increases c) false, HF is a weak acid, weaker than the other H halides, primarily because the H-F bond energy is exceptionally high 32. a) HBr acts as the H + donor (B-L Acid) toward H 2 O (B-L base) b) H - acts like a B-L base, forming H 2 and OH - c) pyridine acts like a Lewis base, SO 2 is Lewis acid d) SO 2 acts as a Lewis acid, H 2 O is the Lewis base 33. a) LA = HNO 2 ; LB = OH - b) LA = FeBr 3 ; LB = Br - c) LA = Zn 2+ ; LB = NH 3 d) LA = SO 2 ; LB = H 2 O

6 34. a) BH 3 vacant valence shell b) SO 3 electronegative O atoms will draw e - density from S and make it an e - acceptor c) HBr H + accepts e - much more readily than H - d) Mo 4+ - higher cation charge 35. a) A; b) A; c) A; d) B 36. Strongest base has the highest K b. OH - NH 3 C 2 H 3 O 2 - H 2 O Br -