Buffer Solutions Overview: Definitions, Examples, and Math
Fundamentals of buffer solutions including definitions, strengths, preparation methods, example systems, and mathematical calculations using the Henderson-Hasselbalch equation. Discover how buffers work, their capacity, and effectiveness through practical examples.
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CHE 112 Spring 2021 Lecture 14 d Buffer Solutions Overview/Topics Skills to Master 1. Definition of Buffers 2. Buffer Strengths 3. Making Buffer Solutions 4. Examples of Buffer Systems 5. Buffer Math 6. Henderson-Hasselbalch Equation (HHE) 1. HW 14 d Read OER 14.5-14.6
Buffers o Solutions that are resistant to changes in pH o wa + salt of conjugate base o wb + salt of conjugate acid Salt = anion of SA cation of SB Weak Acid Salt of Weak Acid Replace H with Metal Ion
How Buffers Work Acid + Base = Salt + Water HC2H3O2 + NaOH NaC2H3O2 + H2O Salt CB + Acid = Weak Acid + Salt NaC2H3O2 + HCl HC2H3O2 + NaCl Equilibrium H3O+ (aq) + C2H3O2- (aq) HC2H3O2 (aq) + H2O (l)
You Try It: Which of the following is a Buffer Systems? (a) H2SO4 / Na2SO4 (b) HF / KF (c) NH3 / NH4Cl (d) NaOH / KOH (e) HC2H2O2 / HF You Try It: To make a buffer system you could add which of the following to HNO2: (a) HNO3 (b) NaNO2 (c) NaOH (d) Mg(NO2)2 (e) KC2H3O2
Buffer Capacity Buffer Effectiveness o DP to [ ] o DP to Volume o Ratio of [A]:[B] o Most effective near 1 o Acceptable 0.1-10 o pKa = +/- 1 of desired pH
Review Ch. 13 Buffer Math 1. Write eqn 2. ICE chart 3. Choose x 4. Solve 5. Calc. pH 1. pH HF 2. Initial pH of Buffer 3. pH after addition of base 4. pH after addition of acid 0.1 M HF Ka (HF) = 7.1 x 10-5 pH of pure HF Solution:
0.1 M HF + 0.1 M NaF Ka (HF) = 7.1 x 10-5 pH Initial Solution:
0.1 M HF + 0.1 M NaF Ka (HF) = 7.1 x 10-5 Add 0.01 M NaOH pH after addition of Base: Compare to 0.01 M NaOH alone
0.1 M HF + 0.1 M NaF Ka (HF) = 7.1 x 10-5 Add 0.01 M HCl pH after addition of Acid: Compare to 0.01 M HCl alone
Summary: Solution pH Pure 0.1 M HF: 2.07 Buffer 0.1 M HF and 0.1 M NaF 4.15 After adding Base: 4.23 After adding Acid: 4.06
Buffer vs No Buffer: o Calculate the [HCl] required to have the same pH as a 0.1 M HF + 0.1 M (4.15) o Calculate the pH after addition of 0.01 M NaOH o Compare the Buffered system and Non-buffered system
Henderson-Hasselbalch Equation Buffer Shortcut ?? = ???+ log[????] [????] Double Check! [Acid] > [Base] then pH < pKa [Acid] = [Base] then pH = pKa [Acid] < [Base] then pH > pKa
Example: What is the pH of a buffer made from 0.2 M NH3 and 0.3 M NH4Cl? From Appendix Kb = 1.8 x 10-5
Example: Prepare a buffer with pH = 4.0 From Appendix Compound pKa 3.77 Formic Acid Lactic Acid 3.85 Ascorbic Acid 4.10 Benzoic Acid 4.20
Example: Prepare a buffer with pH = 9.0 From Appendix
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