University:
Boston University
Course:
CAS CH 102 | General Chemistry 2
Academic year:

2020
Views:

444

Pages:

3
Author:

presareb6f5

Challenge: Buffer A buffer is constructed by dissolving in water at 25 oC 1.00 mol Boston Title Goes eachUniversity of an Slideshow acid, with KaHere = 1 x 10‒5, and its conjugate base in a total volume of 1.00 L. What is the pH after 500. mL of 0.100 M HCl has been added to the original buffer solution? Answer: pH = 4.96 What is the pH after 500. mL of 0.100 M NaOH has been added to the original buffer solution? Answer: pH = 5.04 Add strong acid to buffer Boston University Slideshow Title Goes Here 1 L buffer, ca = cb = 1.00 M, Ka = 1 x 10‒5 , pH = 5.00 Add 500. mL of 0.100 M HCl HCl(aq) + ↓A−(aq)  ↑HA(aq) + Cl−(aq) HA  1.00 mol + 0.050 mol = 1.05 mol A−  1.00 mol ‒ 0.050 mol = 0.95 mol ca = 1.05 mol/1.50 L, cb = 0.95 mol/1.50 L ca/cb = 1.00  1.05/0.95, pH  4.96 (tiny change!) Add strong base to buffer 1 L buffer, ca = cb = 1.00 M, Ka = 1 x 10‒5 , pH = … 5.00 Add 500. mL of 0.100 M NaOH ↓HA(aq) + OH−(aq)  H2O(l) + ↑A‐(aq) HA  1.00 mol – 0.050 mol = 0.95 mol A−  1.00 mol + 0.050 mol = 1.05 mol ca = 0.95 mol/1.50 L, cb = 1.05 mol/1.50 L ca/cb = 1.00  0.95/1.01, pH  5.04 (tiny change!)