Buffer capacity refers to the amount of acid or base a buffer can absorb without a significant pH change. It is governed by the concentrations of the conjugate acid and base components of the buffer. A 0.5 M buffer can “absorb” five times as much acid or base as a 0.1 M buffer for a given pH change. In the next three problems you begin with a buffer of known pH and concentration and calculate the new pH after a particular quantity of acid or base is added. You are given 60 mL of 0.50 M phosphate buffer, pH = 6.83, to test. The starting composition of the buffer, both in terms of the concentration and the molar quantity of the two major phosphate species, is: Concentration of HPO42−: 0.304 M Molar quantity of HPO42−: 18.2 mmol Concentration of H2PO4−: 0.196 M Molar quantity of H2PO4−: 11.8 mmol
Buffer capacity refers to the amount of acid or base a buffer can absorb without a significant pH change. It is governed by the concentrations of the conjugate acid and base components of the buffer. A 0.5 M buffer can “absorb” five times as much acid or base as a 0.1 M buffer for a given pH change. In the next three problems you begin with a buffer of known pH and concentration and calculate the new pH after a particular quantity of acid or base is added. You are given 60 mL of 0.50 M phosphate buffer, pH = 6.83, to test. The starting composition of the buffer, both in terms of the concentration and the molar quantity of the two major phosphate species, is: Concentration of HPO42−: 0.304 M Molar quantity of HPO42−: 18.2 mmol Concentration of H2PO4−: 0.196 M Molar quantity of H2PO4−: 11.8 mmol
Chemistry
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ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
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Chapter1: Chemical Foundations
Section: Chapter Questions
Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...
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Buffer capacity refers to the amount of acid or base a buffer can absorb without a significant pH change. It is governed by the concentrations of the conjugate acid and base components of the buffer. A 0.5 M buffer can “absorb” five times as much acid or base as a 0.1 M buffer for a given pH change. In the next three problems you begin with a buffer of known pH and concentration and calculate the new pH after a particular quantity of acid or base is added.
You are given 60 mL of 0.50 M phosphate buffer, pH = 6.83, to test. The starting composition of the buffer, both in terms of the concentration and the molar quantity of the two major phosphate species, is:
| Concentration of HPO42−: 0.304 M | Molar quantity of HPO42−: 18.2 mmol |
| Concentration of H2PO4−: 0.196 M | Molar quantity of H2PO4−: 11.8 mmol |
a. What is the new HPO42−/H2PO4− ratio, and the new pH of the solution? The pKa of H2PO4− is 6.64. Use the Henderson-Hasselbalch equation to calculate the new pH. (Note: You can use the molar ratio rather than the concentration ratio because both species are in the same volume.)
|
HPO42−/H2PO4− ratio
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|---|---|
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pH of the solution
|
b.
Now take a fresh 60 mL of the 0.50 M pH 6.83 buffer and add 3.7 mL of 1.00 M NaOH. Using steps similar to those above, calculate the new pH of the solution.
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