A buffer is prepared by mixing 65.7 mL of 0.450 M HC7H5O2 with 35.0 mL of 0.643 M KC7H5O2. Ka = 6.3 x 10-5 Determine the pH for this buffer. What will be the pH after the addition of 0.015 mol HBr? Assume the volume does not change.
A buffer is prepared by mixing 65.7 mL of 0.450 M HC7H5O2 with 35.0 mL of 0.643 M KC7H5O2. Ka = 6.3 x 10-5 Determine the pH for this buffer. What will be the pH after the addition of 0.015 mol HBr? Assume the volume does not change.
Chemistry: Principles and Reactions
8th Edition
ISBN:9781305079373
Author:William L. Masterton, Cecile N. Hurley
Publisher:William L. Masterton, Cecile N. Hurley
Chapter14: Equilibria In Acid-base Solutions
Section: Chapter Questions
Problem 12QAP: A buffer is prepared by dissolving 0.062 mol of sodium fluoride in 127 mL of 0.0399 M hydrofluoric...
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A buffer is prepared by mixing 65.7 mL of 0.450 M HC7H5O2 with 35.0 mL of 0.643 M KC7H5O2. Ka = 6.3 x 10-5
- Determine the pH for this buffer.
- What will be the pH after the addition of 0.015 mol HBr? Assume the volume does not change.
Expert Solution
Step 1
pH = pKa + log [Salt]/[Acid]
pKa = -log Ka
Step 2
Answer 1:
Number of mole of HC7H5O2 = Molarity x volume in L = 0.450 x 0.0657 = 0.029565
Number of mole of KC7H5O2 = Molarity x volume in L = 0.643 x 0.035 = 0.022505
Total volume after mixing = 65.7 mL + 35.0 = 100.7 mL = 0.1007 L
[HC7H5O2] = 0.029565/0.1007
[KC7H5O2] = 0.022505/0.1007
pKa = -log Ka = -log 6.3 x 10-5 = 4.20
pH = pKa + log [KC7H5O2]/[HC7H5O2]
= 4.20 + log 0.022505/0.029565
= 4.20 + log 22505 - log 29565
= 4.20 + 4.35 - 4.47
= 4.08
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