1) Create a buffer solution of pH= 4.75 from 1M acetic acid (HA)and 1M sodium acetate (NaA) solution (total volume 100 mL): Use PKa = 4.75 Use H-H equation to find the molar ratio of HA and NaA; mix both solutions so that total volume 100 mL or near 100. mL 2) Calculate to find new pH value if 1.00 mL of 10 M HCI is added to the buffer created above. solution

1) Create a buffer solution of pH= 4.75 from 1M acetic acid (HA)and 1M sodium acetate (NaA) solution (total volume 100 mL): Use PKa = 4.75 Use H-H equation to find the molar ratio of HA and NaA; mix both solutions so that total volume 100 mL or near 100. mL 2) Calculate to find new pH value if 1.00 mL of 10 M HCI is added to the buffer created above. solution

Principles of Modern Chemistry

8th Edition

ISBN:9781305079113

Author:David W. Oxtoby, H. Pat Gillis, Laurie J. Butler

Publisher:David W. Oxtoby, H. Pat Gillis, Laurie J. Butler

Chapter15: Acid–base Equilibria

Section: Chapter Questions

Problem 45P

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Enough water is added to the buffer in Question 30 to make the total volume 5.00 L. (a) Calculate the pH of the buffer. (b) Calculate the pH of the buffer after adding 0.0250 mol of HCl to 0.376 L of the buffer. (c) Calculate the pH of the buffer after adding 0.0250 mol of KOH to 0.376 L of the buffer. (d) Compare your answers to Question 30 (a-c) with your answers to (a-c) of this problem. (e) Comment on the effect of dilution on the pH of a buffer and on its buffer capacity. Â
Sketch a titration curve for the titration of potassium hydroxide with HCl, both 0.100 M. Identify three regions in which a particular chemical species or system dominates the acid-base equilibria.
You have 0.10-mol samples of three acids identified simply as HX, HY, and HZ. For each acid, you make up 0.10 M solutions by adding sufficient water to each of the acid samples. When you measure the pH of these samples, you find that the pH of HX is greater than the pH of HY, which in turn is greater than the pH of HZ. a Which of the acids is the least ionized in its solution? b Which acid has the largest Kd?
Sketch the titration curve for a weak acid titrated by a strong base. When performing calculations concerning weak acidstrong base titrations, the general two-slep procedure is to solve a stoichiometry problem first, then to solve an equilibrium problem to determine the pH. What reaction takes place in the stoichiometry part of the problem? What is assumed about this reaction? At the various points in your titration curve, list the major species present after the strong base (NaOH, for example) reacts to completion with the weak acid, HA. What equilibrium problem would you solve at the various points in your titration curve to calculate the pH? Why is pH 7.0 at the equivalence point of a weak acid-strong base titration? Does the pH at the halfway point to equivalence have to be less than 7.0? What does the pH at the halfway point equal? Compare and contrast the titration curves for a strong acidstrong base titration and a weak acidstrong base titration.
Consider a solution formed by mixing 100.0 mL of 0.10 M HA (Ka = 1.0 106), 100.00 mL of 0.10 M NaA. and 100.0 mL of 0.10 M HCl. In calculating the pH for the final solution, you would make some assumptions about the order in which various reactions occur to simplify the calculations. State these assumptions. Does it matter whether the reactions actually occur in the assumed order? Explain.
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?