Which one of the following would make the best buffer? (Ac = acetate) O a solution of ammonia and ammonium chloride, NH3 and NH4Cl O a solution of hydrochloric acid and sodium chloride, HCl and NaCl a solution of acetic acid and ammonium chloride, HAC and NH4CI O a solution of acetic acid and ammonia, NaAc and NH3

Which one of the following would make the best buffer? (Ac = acetate) O a solution of ammonia and ammonium chloride, NH3 and NH4Cl O a solution of hydrochloric acid and sodium chloride, HCl and NaCl a solution of acetic acid and ammonium chloride, HAC and NH4CI O a solution of acetic acid and ammonia, NaAc and NH3

Chemistry: An Atoms First Approach

2nd Edition

ISBN:9781305079243

Author:Steven S. Zumdahl, Susan A. Zumdahl

Publisher:Steven S. Zumdahl, Susan A. Zumdahl

Chapter14: Acid- Base Equilibria

Section: Chapter Questions

Problem 3ALQ

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Each symbol in the box below represents a mole of a component in one liter of a buffer solution; represents the anion (X-), = the weak acid (HX), = H+, and =OH. Water molecules and the few H+ and OH- ions from the dissociation of HX and X- are not shown. The box contains 10 mol of a weak acid, , in a liter of solution. Show what happens upon (a) the addition of 2 mol of OH- (2 ). (b) the addition of 5 mol of OH- (5 ). (c) the addition of 10 mol of OH- (10 ). (d) the addition of 12 mol of OH- (12 ). Which addition (a)-(d) represents neutralization halfway to the equivalence point?
When 40.00 mL of a weak monoprotic acid solution is titrated with 0.100-M NaOH, the equivalence point is reached when 35.00 mL base has been added. After 20.00 mL NaOH solution has been added, the titration mixture has a pH of 5.75. Calculate the ionization constant of the acid.
A friend asks the following: Consider a buffered solution made up of the weak acid HA and its salt NaA. If a strong base like NaOH is added, the HA reacts with the OH to form A. Thus the amount of acid (HA) is decreased, and the amount of base (A) is increased. Analogously, adding HCI to the buffered solution forms more of the acid (HA) by reacting with the base (A). Thus how can we claim that a buffered solution resists changes in the pH of the solution? How would you explain buffering to this friend?
What is the pH of a buffer that is 0.175 M in a weak acid and 0.200 M in the acids conjugate base? The acids ionization constant is 5.7 104.
A diprotic acid, H2B(MM=126g/moL), is determined to be a hydrate, H2B xH2O. A 10.00-g sample of this hydrate is dissolved in enough water to make 150.0 mL of solution. Twenty-five milliliters of this solution requires 48.5 mL of 0.425 M NaOH to reach the equivalence point. What is x?
A sodium hydrogen carbonate-sodium carbonate buffer is to be prepared with a pH of 9.40. (a) What must the [ HCO3 ]/[ CO32 ]ratio be? (b) How many moles of sodium hydrogen carbonate must be added to a liter of 0.225 M Na2CO3 to give this pH? (c) How many grams of sodium carbonate must be added to 475 mL of 0.336 M NaHCO3 to give this pH? (Assume no volume change.) (d) What volume of 0.200 M NaHCO3 must be added to 735 mL of a 0.139 M solution of Na2CO3 to give this pH? (Assume that volumes are additive.)
Consider the weak acids in Table 13.2. Which acid-base pair would be best for a buffer at a pH of (a) 3.0(b) 6.5 (c) 12.0
What mass of NH4Cl must be added to 0.750 L of a 0.100-M solution of NH3 to give a buffer solution with a pH of 9.26? (Him: Assume a negligible change in volume as the solid is added.)
A good buffer generally contains relatively equal concentrations of weak acid and conjugate base. If you wanted to buffer a solution at pH = 4.00 or pH = 10.00, how would you decide which weak acidconjugate base or weak baseconjugate acid pair to use? The second characteristic of a good buffer is good buffering capacity. What is the capacity of a buffer? How do the following buffers differ in capacity? How do they differ in pH? 0.01 M acetic acid/0.01 M sodium acetate 0.1 M acetic acid/0.1 M sodium acetate 1.0 M acetic acid/1.0 M sodium acetate
Metacresol purple is an indicator that changes from yellow to purple at pH 8.2. (a) What is Ka for this indicator? (b) What is its pH range? (c) What is the color of a solution with pH 9.0 and a few drops of metacresol purple?
Vitamin C is a monoprotic acid. To analyze a vitamin C capsule weighing 0.505 g by titration took 24.4 mL of 0.110-M NaOH. Calculate the percentage of vitamin C, C6H8O6, in the capsule. Assume that vitamin C is the only substance in the capsule that reacts with the titrant.
a Draw a pH titration curve that represents the titration of 50.0 mL of 0.10 M NH3 by the addition of 0.10 M HCl from a buret. Label the axes and put a scale on each axis. Show where the equivalence point and the buffer region are on the titration curve. You should do calculations for the 0%, 30%, 50%, and 100% titration points. b Is the solution neutral, acidic, or basic at the equivalence point? Why?