8. K/U Write the base-dissociation constant expressions for the conjugate base of each of the following weak acids: a. oxalic acid, HOOCCOOH(aq) b. ascorbic acid, C,H,O6(aq) c. sulfurous acid, H₂SO3(aq)

8. K/U Write the base-dissociation constant expressions for the conjugate base of each of the following weak acids: a. oxalic acid, HOOCCOOH(aq) b. ascorbic acid, C,H,O6(aq) c. sulfurous acid, H₂SO3(aq)

Chemistry for Engineering Students

4th Edition

ISBN:9781337398909

Author:Lawrence S. Brown, Tom Holme

Publisher:Lawrence S. Brown, Tom Holme

Chapter12: Chemical Equilibrium

Section: Chapter Questions

Problem 12.65PAE

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Strong Acids, Weak Acids, and pH Two 0.10-mol samples of the hypothetical monoprotic acids HA(aq) and HB(aq) are used to prepare 1.0-L stock solutions of each acid. a Write the chemical reactions for these acids in water. What are the concentrations of the two acid solutions? b One of these acids is a strong acid, and one is weak. What could you measure that would tell you which acid was strong and which was weak? c Say that the HA(aq) solution has a pH of 3.7. Is this the stronger of the two acids? How did you arrive at your answer? d What is the concentration of A(aq) in the HA solution described in part c? e If HB(aq) is a strong acid, what is the hydronium-ion concentration? f In the solution of HB(aq), which of the following would you expect to be in the greatest concentration: H3O+(aq), B(aq), HB(aq), or OH(aq)? How did you decide? g In the solution of HA(aq), which of the following would you expect to be in the greatest concentration: H3O+(aq), A+(aq), HA(aq), or OH(aq)? How did you decide? h Say you add 1.0 L of pure water to a solution of HB. Would this water addition make the solution more acidic, make it less acidic, or not change the acidity of the original solution? Be sure to fully justify your answer. i You prepare a 1.0-L solution of HA. You then take a 200-mL sample of this solution and place it into a separate container. Would this 200 mL sample be more acidic, be less acidic, or have the same acidity as the original 1.0-L solution of HA(aq)? Be sure to support your answer.
Table 13-4 lists the stepwise Ka values for some polyprotic acids. What is the difference between a monoprotic acid, a diprotic acid, and a triprotic acid? Most polyprotic acids are weak acids; the major exception is H2SO4. To solve for the pH of a solution of H2SO4, you must generally solve a strong acid problem as well as a weak acid problem. Explain. Write out the reactions that refer to Ka1 and Ka2 for H2SO4. For H3PO4, Ka1 = 7.5 103, Ka2 = 6.2 108, and Ka3= 4.8 1013. Write out the reactions that refer to the Ka1, Ka2and Ka3equilibrium constants. What are the three acids in a solution of H3PO4? Which acid is strongest? What are the three conjugate bases in a solution of H3PO4? Which conjugate base is strongest? Summarize the strategy for calculating the pH of a polyprotic acid in water.
Ionization of the first proton from H2SeO4 is complete (H2SeO4 is a strong acid); the acid-ionization constant for the second proton is 1.2 102. a What would be the approximate hydronium-ion concentration in 0.150 M H2SeO4 if ionization of the second proton were ignored? b The ionization of the second proton must be considered for a more exact answer, however. Calculate the hydronium-ion concentration in 0.150 M H2SeO4, accounting for the ionization of both protons.
Write the reaction and the corresponding Kb equilibrium expression for each of the following substances acting as bases in water. a. aniline, C6H5NH2 b. dimethylamine, (CH3)2NH
Aqueous Solutions of Acids, Bases, and Salts a For each of the following salts, write the reaction that occurs when it dissociates in water: NaCl(s), NaCN(s), KClO2(s), NH4NO3(s), KBr(aq), and NaF(s). b Consider each of the reactions that you wrote above, and identify the aqueous ions that could be proton donors (acids) or proton acceptors (bases). Briefly explain how you decided which ions to choose. c For each of the acids and bases that you identified in pan b, write the chemical reaction it can undergo in aqueous solution (its reaction with water). d Are there any reactions that you have written above that you anticipate will occur to such an extent that the pH of the solution will be affected? As pan of your answer, be sure to explain how you decided. e Assume that in each case above, 0.01 mol of the salt was dissolved in enough water at 25C to make 1.0 L of solution. In each case what additional information would you need in order to calculate the pH? If there are cases where no additional information is required, be sure to state that as well. f Say you take 0.01 mol of NH4CN and dissolve it in enough water at 25C to make 1.0 L of solution. Using chemical reactions and words, explain how you would go about determining what effect this salt will have on the pH of the solution. Be sure to list any additional information you would need to arrive at an answer.
For oxyacids, how does acid strength depend on a. the strength of the bond to the acidic hydrogen atom? b. the electronegativity of the element bonded to the oxygen atom that bears the acidic hydrogen? c. the number of oxygen atoms? How does the strength of a conjugate base depend on these factors? What type of solution forms when a nonmetal oxide dissolves in water? Give an example of such an oxide. What type of solution forms when a metal oxide dissolves in water? Give an example of such an oxide.
12.63 For each of the following reactions, indicate the Bronsted-Lowrv acids and bases. What are the conjugate acid-base pairs? CN’(aq) + H2O(€) «=* HCN(aq) + OH’(aq) HCO}-(aq) + H,o+(aq) +* H2CO,(aq) + H,O(€) (C) CH,CtX)H(aq) + HS~(aq)i=i CH}COO"(aq) + H2S(aq)
Are solutions of the following salts acidic, basic, or neutral? For those that are not neutral, write balanced chemical equations for the reactions causing the solution to be acidic or basic. The relevant Ka and Kb values are found in Tables 13-2 and 13-3. a. NaNO3 b. NaNO2 c. C5H5NHClO4 d. NH4NO2 e. KOCl f. NH4OCl
In each of the following acid-base reactions, identify the Brnsted acid and base on the left and their conjugate partners on the right. (a) HCO2H(aq) + H2O() HCO2(aq) + H3O+(aq) (b) NH3(aq) + H2S(aq) NH4+(aq) + HS(aq) (c) HSO4(aq) + OH(aq) SO42(aq) + H2O+()
Consider a solution prepared by mixing a weak acid HA. HCl, and NaA. Which of the following statements best describes what happens? a. The H+ from the HCl reacts completely with the A from the NaA. Then the HA dissociates somewhat. b. The H+ from the HCl reacts somewhat with the A from the NaA to make HA, while the HA is dissociating. Eventually you have equal amounts of everything. c. The H+ from the HCl reacts somewhat with the A from the NaA to make HA while the HA is dissociating. Eventually all the reactions have equal rates. d. The H+ from the HCl reacts completely with the A from the NaA. Then the HA dissociates somewhat until too much H+ and A are formed, so the H+ and A react to form HA, and so on. Eventually equilibrium is reached. Justify your choice, and for choices you did not pick, explain what is wrong with them.
In the following reaction of tetrafluoroboric acid, HBF4, with the acetate ion, C2H3O2, the formation of tetrafluoroborate ion, BF4 , and acetic acid, HC2H3O2 is favored. HBF4+C2H3O2BF4+HC2H3O2 Which is the weaker base, BF4 or acetate ion?
. The concepts of acid-base equilibria were developed in this chapter for aqueous solutions (in aqueous solutions, water is the solvent and is intimately involved in the equilibria). However, the Brønsted-Lowry acid-base theory can be extended easily to other solvents. One such solvent that has been investigated in depth is liquid ammonia. NH3. a. Write a chemical equation indicating how HCl behaves as an acid in liquid ammonia. b. Write a chemical equation indicating how OH- behaves as a base in liquid ammonia.