-9 What mas of A chemistry graduate student is given 125. mL of a 0.20 M pyridine (C,H;N) solution. Pyridine is a weak base with K, = 1.7 × 10 C;H;NHC1 should the student dissolve in the C,H;N solution to turn it into a buffer with pH = 5.69? You may assume that the volume of the solution doesn't change when the C,H;NHC1 is dissolved in it. Be sure your answer has a unit symbol, and round it to 2 significant digits.

-9 What mas of A chemistry graduate student is given 125. mL of a 0.20 M pyridine (C,H;N) solution. Pyridine is a weak base with K, = 1.7 × 10 C;H;NHC1 should the student dissolve in the C,H;N solution to turn it into a buffer with pH = 5.69? You may assume that the volume of the solution doesn't change when the C,H;NHC1 is dissolved in it. Be sure your answer has a unit symbol, and round it to 2 significant digits.

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 4RQ: A good buffer generally contains relatively equal concentrations of weak acid and conjugate base. If...

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Sketch two pH curves, one for the titration of a weak acid with a strong base and one for a strong acid with a strong base. How are they similar? How are they different? Account for the similarities and the differences.
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Sketch a pH curve for the titration of a weak acid (HA) with a strong base (NaOH). List the major species, and explain how you would go about calculating the pH of the solution at various points, including the halfway point and the equivalence point.
Fifty cm3 of 1.000 M nitrous acid is titrated with 0.850 M NaOH. What is the pH of the solution (a) before any NaOH is added? (b) at half-neutralization? (c) at the equivalence point? (d) when 0.10 mL less than the volume of NaOH to reach the equivalence point is added? (e) when 0.10 mL more than the volume of NaOH to reach the equivalence point is added? (f) Use your data to construct a plot similar to that shown in Figure 14.10 (pH versus volume NaOH added).
A buffer solution with it pH of 12.00 consists of Na3PO4 and Na2HPO4. The volume of solution is 200.0 mL. (a) Which component of the buffer is present in a larger amount? (b) If the concentration of Na3PO4 is 0.400 M, what mass of Na2HPO4 is present? (c) Which component of the buffer must be added to change the pH to 12.25? What mass of that component is required?
You want to make a buffer with a pH of 10.00 from NH4+/NH3. (a) What must the [ NH4+ ]/[ NH3 ]ratio be? (b) How many moles of NH4Cl must be added to 465 mL of an aqueous solution of 1.24 M NH3 to give this pH? (c) How many milliliters of 0.236 M NH3 must be added to 2.08 g of NH4Cl to give this pH? (d) What volume of 0.499 M NH3 must be added to 395 mL, of 0.109 M NH4Cl to give this pH?
The weak base ethanolamine. HOCH2CH2NH2, can be titrated with HCl. HOCH2CH2NH2(aq)+H3O+(aq)HOCH2CH2NH3+(aq)+H2O(l) Assume you have 25.0 mL of a 0.010 M solution of ethanolamine and titrate it with 0.0095 M HCl. (Kb for ethanolamine is 3.2 107.) (a) What is the pH of the ethanolamine solution before the titration begins? (b) What is the pH at the equivalence point? (c) What is the pH at the halfway point of the titration? (d) Which indicator in Figure 17.11 would be the best choice to detect the equivalence point? (e) Calculate the pH of the solution after adding 5.00, 10.0, 20.0, and 30.0 mL of the acid. (f) Combine the information in parts (a), (b), (c), and (e), and plot an approximate titration curve.
A buffer is made using 45.0 mL of 0.750 M HC3H5O2 (Ka = 1.3 105) and 55.0 mL of 0.700 M NaC3H5O2. What volume of 0.10 M NaOH must be added to change the pH of the original buffer solution by 2.5%?
Consider 0.0010-M solutions of these sparingly soluble solutes in equilibrium with their ions. Predict the effect on each equilibrium if a saturated solution of sodium iodide were added. Explain your prediction in each case. AgI(s) ⇌ Ag+(aq) + I−(aq) PbI2(s) ⇌ Pb2+(aq) + 2 I−(aq)
8-93 Do a 1.0 M CH3COOH solution and a 1.0 M HCI solution require the same amount of 1.0 M NaOH to hit a titration end point? Explain.
The simplest amino acid is glycine, H2NCH2CO2H. The common feature of amino acids is that they contain the functional groups: an amine group, -NH2, and a carboxylic acid group, -CO2H. An amino acid can function as either an acid or a base. For glycine, the acid strength of the carboxyl group is about the same as that of acetic acid. CH3CO2H, and the base strength of the amino group is slightly greater than that of ammonia, NH3. (a) Write the Lewis structures of the ions that form when glycine is dissolved in 1 M HCl and in 1 M KOH. (b) Write the Lewis structure of glycine when this amino acid is dissolved in water. (Hint: Consider the relative base strengths of the -NH2 and -CO2- groups.)
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