Four so V s of an acid dissolved in water are sketched below, as if under a microscope so powerful individual atoms could be seen. The same volume of solution is shown in each sketch. Rank the solutions by the strength of the dissolved acid. That is, select1 under the solution of the strongest acid, 2 under the solution of the next strongest add, and so on. Note: =H,0 Solution 1 Solution 2 1 (strongest acid) Solution 3 Solution 4 4 (weakest acid)

Four so V s of an acid dissolved in water are sketched below, as if under a microscope so powerful individual atoms could be seen. The same volume of solution is shown in each sketch. Rank the solutions by the strength of the dissolved acid. That is, select1 under the solution of the strongest acid, 2 under the solution of the next strongest add, and so on. Note: =H,0 Solution 1 Solution 2 1 (strongest acid) Solution 3 Solution 4 4 (weakest acid)

Chemistry

10th Edition

ISBN:9781305957404

Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste

Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste

Chapter14: Acids And Bases

Section: Chapter Questions

Problem 7RQ: Table 13-4 lists the stepwise Ka values for some polyprotic acids. What is the difference between a...

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. How is the strength of an acid related to the fact that a competition for protons exists in aqueous solution between water molecules and the anion of the acid?
In dilute aqueous solution HF acts as a weak acid. However, pure liquid HF (boiling point = 19.5 C) is a strong acid. In liquid HF, HNO3 acts like a base and accepts protons. The acidity of liquid HF can be increased by adding one of several inorganic fluorides that ale Lewis acids and accept F- ion (for example, BF3 or SbF5]. Write balanced chemical equations for the reaction of pure HNO3 with pure HF and of pure HF with BF3.
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.
Malic acid is a weak diprotic organic acid with Ka1 = 4.0 104 and Ka2 = 9.0 105. a Letting the symbol H2A represent malic acid, write the chemical equations that represent Ka1 and Ka2. Write the chemical equation that represents Ka1 Ka2. b Qualitatively describe the relative concentrations of H2A, HA, A2, and H3O+ in a solution that is about one molar in malic acid. c Calculate the pH of a 0.0175 M malic acid solution and the equilibrium concentration of [H2A]. d What is the A2 concentrationin in solutions b and c?
Composition diagrams, commonly known as alpha plots, are often used to visualize the species in a solution of an acid or base as the pH is varied. The diagram for 0.100 M acetic acid is shown here. The plot shows how the fraction [alpha ()] of acetic acid in solution, =[CH3CO2H][CH3CO2H]+[CH3CO2] changes as the pH increases (blue curve). (The red curve shows how the fraction of acetate ion, CH3CO2, changes as the pH increases.) Alpha plots are another way of viewing the relative concentrations of acetic acid and acetate ion as a strong base is added to a solution of acetic acid in the course of a titration. (a) Explain why the fraction of acetic acid declines and that of acetate ion increases as the pH increases. (b) Which species predominates at a pH of 4, acetic acid or acetate ion? What is the situation at a pH of 6? (c) Consider the point where the two lines cross. The fraction of acetic acid in the solution is 0.5, and so is that of acetate ion. That is, the solution is half acid and half conjugate base; their concentrations are equal. At this point, the graph shows the pH is 4.74. Explain why the pH at this point is 4 74.
For conjugate acidbase pairs, how are Ka and Kb related? Consider the reaction of acetic acid in water CH3CO2H(aq)+H2O(l)CH3CO2(aq)+H3O+(aq) where Ka = 1.8 105 a. Which two bases are competing for the proton? b. Which is the stronger base? c. In light of your answer to part b. why do we classify the acetate ion (CH3CO2) as a weak base? Use an appropriate reaction to justify your answer. In general, as base strength increases, conjugate acid strength decreases. Explain why the conjugate acid of the weak base NH3 is a weak acid. To summarize, the conjugate base of a weak acid is a weak base and the conjugate acid of a weak base is a weak acid (weak gives you weak). Assuming Ka for a monoprotic strong acid is 1 106, calculate Kb for the conjugate base of this strong acid. Why do conjugate bases of strong acids have no basic properties in water? List the conjugate bases of the six common strong acids. To tie it all together, some instructors have students think of Li+, K+, Rb+, Cs+, Ca2+, Sr2+, and Ba2+ as the conjugate acids of the strong bases LiOH, KOH. RbOH, CsOH, Ca(OH)2, Sr(OH)2, and Ba(OH)2. Although not technically correct, the conjugate acid strength of these cations is similar to the conjugate base strength of the strong acids. That is, these cations have no acidic properties in water; similarly, the conjugate bases of strong acids have no basic properties (strong gives you worthless). Fill in the blanks with the correct response. The conjugate base of a weak acid is a_____base. The conjugate acid of a weak base is a_____acid. The conjugate base of a strong acid is a_____base. The conjugate acid of a strong base is a_____ acid. (Hint: Weak gives you weak and strong gives you worthless.)
Weak base B has a pKb of 6.78 and weak acid HA has a pKa of 5.12. a Which is the stronger base, B or A? b Which is the stronger acid, HA or BH+? c Consider the following reaction: B(aq)+HA(aq)BH+(aq)+A(aq) Based on the information about the acid/base strengths for the species in this reaction, is this reaction favored to proceed more to the right or more to the left? Why? d An aqueous solution is made in which the concentration of weak base B is one half the concentration of its acidic salt, BHCl, where BH+ is the conjugate weak add of B. Calculate the pH of the solution. e An aqueous solution is made in which the concentration of weak acid HA twice the concentration of the sodium salt of the weak acid, NaA. Calculate the pH of the solution. f Assume the conjugate pairs B/BH+ and HA/A are capable of being used as color-based end point indicators in acidbase titrations, where B is the base form indicator and BH is the acid form indicator, and HA is the acid form indicator and A is the base form indicator. Select the indicator pair that would be best to use in each of the following titrations: (1) Titration of a strong acid with a strong base. (i) B/BH+ (ii) HA/A (2) Titration of a weak base with a strong acid. (i) B/BH+ (ii) HA/A
. 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.
Develop a set of rules by which you could predict the pH for solutions of strong or weak acids and strong or weak bases without using a calculator. Your predictions need to be accurate to 1 pH unit. Assume that you know the concentration of the acid or base and that for the weak acids and bases you can look up the pKa (log Ka) or Ka values. What rules would work to predict pH?
Consider all acid-base indicators discussed in this chapter. Which of these indicators would be suitable for the titration of each of these? (a) NaOH with HClO4 (b) acetic acid with KOH (c) NH3 solution with HBr (d) KOH with HNO3 Explain your choices.
A solution is made by diluting 25.0 mL of concentrated HCl (37% by weight; density = 1.19 g/mL) to exactly 500 mL. Calculate the pH of the resulting solution.
Repeat the description for Question 4, but use a weak acid rather than a strong one.