1 / 4

PRACTICE QUIZ KEY AQUEOUS EQUILIBRIA (20 points)

PRACTICE QUIZ KEY AQUEOUS EQUILIBRIA (20 points). 1. (2 pts) Which makes a pH 7 buffer?. a. 1 M NaOH and 1 M NaCl b. 1 M HC 2 H 3 O 2 and 1 MNaC 2 H 3 O 2 c. 1 M HCl and 1 M NaCl d. 1 M NH 4 Cl and 1 M NH 3. 2. (10 pts) Calculate the pH. 0.200 M x 0.0750 L = 0.0150 mol

cissy
Download Presentation

PRACTICE QUIZ KEY AQUEOUS EQUILIBRIA (20 points)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. PRACTICE QUIZ KEY AQUEOUS EQUILIBRIA (20 points)

  2. 1. (2 pts) Which makes a pH 7 buffer? • a. 1 M NaOH and 1 M NaCl • b. 1 M HC2H3O2 and 1 MNaC2H3O2 • c. 1 M HCl and 1 M NaCl • d. 1 M NH4Cl and 1 M NH3

  3. 2. (10 pts) Calculate the pH. • 0.200 M x 0.0750 L = 0.0150 mol • Step 1: OH- + HCN W H2O + CN- • Init. 0.0150 0.0150 0 • RXN -0.0150 -0.0150 +0.0150 • Final 0 0 0.0150 mol • (Must be equal at final) • Change mol to M; 0.0150 mol / total volume • V of OH-: V = mol / M = 0.0150 mol / 0.300 M = 0.0500 L • Total volume = 50.0 mL OH- + 75.0 mL HCN = 125.0 mL = 0.125 L • 0.0150 mol CN- / 0.125 L = 0.120 M CN- • Step 2: CN- + H2O W HCN + OH- • 0.120 – x x x • Kb = Kw/Ka = 1.0 x 10-14/4.0 x 10-10 = 2.5 X 10-5 • Kb = [HCN][OH-]/[CN-] = x2 / 0.120 • x = 1.7 x 10-3 = [OH-]; pOH = 2.78; pH = 11.22

  4. 3. (8 pts) What is the pH? • HF W H+ + F- • At equil.: 0.800-x x 0.500+x • Assume “x” is small enough to ignore… • Ka = [H+][F-]/[HF] = 4.0 x 10-4 • 4.0 x 10-4 = x(0.500)/(0.800) • x = 6.4 x 10-4 = [H+] • pH = 3.19

More Related