A buffer is a solution composed of a weak acid with its conjugate base.
Concept #1: A buffer resists drastic changes in pH by keeping constant the acidic and basic ions found in a solution.
Concept #2: The weak acid and conjugate base can be different from one another by up to a magnitude of 10.
Concept #3: The more concentrated the weak acid and conjugate base then the better the buffer can counteract strong acid or strong base added.
Concept #4: A buffer is comprised of a weak acid and its conjugate base that can be formed in 3 different ways.
Example #1: Which of the following combinations can result in the formation of a buffer?
a) 75 mL of 0.10 M HClO3 with 50 mL of 0.10 M CH3NH2.
b) 25 mL of 0.10 M H2SO3 with 40.0 mL of 0.10 M NaOH.
c) 50 mL of 0.10 M NH4Cl with 50 mL of 0.05 M Sr(OH)2.
d) 50 mL of 0.20 M HF with 40 mL of 0.20 M NaOH.
Example #2: Calculate the pH of a solution formed by mixing 130.0 mL of a 0.300 M C2H5NH2 solution with 70.0 mL of a 0.500 M C2H5NH3+ solution. (Kb of C2H5NH2 is 5.0 x 10-4).
Practice: Which of the following molar ratios is the correct equilibrium ratio of BASE : ACID for a solution made of aniline (Kb = 3.8 x 10-10) and anilinium nitrate where the pH is 4.80?
Example #3: You are asked to go into the lab and prepare a buffer solution with a pH of 6.40 ± 0.2. Which weak acid would be the best choice?
a) carbonic acid Ka = 4.2 x 10-7
b) phenol Ka = 1.3 x 10-10
c) ascorbic acid Ka = 8.0 x 10-5
d) hydrosulfuric acid Ka = 9.5 x 10-8
e) potassium hydrogen phthalate Ka = 3.1 x 10-6
Example #4: Calculate the pH of a solution made by mixing 8.627 g of sodium butanoate in enough 0.452 M butanoic acid, HC4H7O2, to make 250.0 mL of solution. The Ka of butanoic acid is 1.5 x 10-5.