Concept explainers
Consider citric acid, H3C6H5O7, added to many soft drinks. The equilibrium constants for its step-wise ionization are
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Chapter 13 Solutions
Chemistry: Principles and Reactions
- Write the chemical equation and the expression for the equilibrium constant, and calculate Kb for the reaction of each of the following ions as a base. (a) sulfate ion (b) citrate ionarrow_forwardFor 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.)arrow_forwardThe pH of a 0.10-M solution of propanoic acid, CH3CH2COOH, a weak organic acid, is measured at equilibrium and found to be 2.93 at 25 °C. Calculate the Ka of propanoic acid.arrow_forward
- Using the diagrams shown in Problem 10-117, which of the solutions would have the greatest buffer capacity, that is, greatest protection against pH change, when the following occurs? a. A strong acid is added to the solution. b. A strong base is added to the solution.arrow_forwardA chemist wanted to determine the concentration of a solution of lactic acid, HC3H5O3. She found that the pH of the solution was 2.60. What was the concentration of the solution? The Kd of lactic acid is 1.4 104.arrow_forwardLactic acid, C3H6O3, occurs in sour milk as a result of the metabolism of certain bacteria. Calculate the pH of a solution of 56. mg lactic acid in 250. mL water. Ka for D-lactic acid is 1.5 × 10−4.arrow_forward
- What is the freezing point of vinegar, which is an aqueous solution of 5.00% acetic acid, HC2H3O2, by mass (d=1.006g/cm3)?arrow_forwardIonization of the first proton from H2SO4 is complete (H2SO4 is a strong acid); the acid-ionization constant for the second proton is 1.1 102. a What would be the approximate hydronium-ion concentration in 0.100 M H2SO4 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 0.100 M H2SO4, accounting for the ionization of both protons.arrow_forwardThe ionization constant of lactic acid, CH3CH(OH)CO2H, an acid found in the blood after strenuous exercise, is 1.36104. If 20.0 g of lactic acid is used to make a solution with a volume of 1.00 L, what is the concentration of hydronium ion in the solution?arrow_forward
- 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)2NHarrow_forwardTable 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.arrow_forwardWrite the acid ionization constant expression for the ionization of each of the following monoprotic acids. a. HCN (hydrocyanic acid) b. HC6H7O6 (ascorbic acid)arrow_forward
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