chemistry worksheet 3
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Chemistry 122 (General College Chemistry I)-‐ Fall 2018 Discussion Worksheet Week 13 (Coordinated by Dr. R. Hatfield)
Topics: Acid Ionic Equlibria Part I: Acid-‐Base Buffers including the common ion effect, Henderson-‐ Hasselbalch equation, buffer capacity and range, buffer preparation Relevant Chapters in Silberberg, 8e: Chapter 19 Section 1, pp. 843-‐853. Student Directions: Try all problems with your best effort and bring your work to discussion. Use your text as a resource for any constants or relationships needed. You will have to work ahead. When topics are completely covered in lecture, go back and redo any problems you did not understand. Thursday and Friday Discussion Sessions Special Instructions: Turn in both week 13 and 14 worksheets during discussion on week 14 for credit.
1. Buffer concepts for discussion a. In your own words, explain the purpose of an acid-‐base buffer.
b. How do the acid and base parts of a buffer function to support the buffer?
c. Describe the common ion effect and how it is related to LeChatelier’s Principle.
2. Working with Aqueous Solutions of HF and NaF a. What is the pH of a 0.35 M hydrofluoric acid (HF) solution? K!= 6.8 x 10-‐4 [1.81]
b. What is the pH of a solution containing 0.35 M HF and 0.28 M NaF? [3.07]
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c. What is the pH after the addition of 0.030 mol of HCl to 1.0 L of the buffer? [2.99]
d. What is the pH after the addition of 0.030 mol of NaOH to 1.0 L of the buffer? [3.16]
e. What is the component concentration ratio, [F!]/[HF], necessary to prepare a solution of this buffer with a pH of 3.35? [1.50]
f. What is the effective buffer range of an F-‐/HF buffer? Explain. [2.17-‐4.17]
g. Define buffer capacity.
h. Which if these factors affect buffer capacity? Explain your answers. [only d.] a. pH of the buffer
b. identity of the conjugate acid-‐base pair
c. buffer range
d. concentration of buffer components
e. pK! of the acid component