NEETChemistryIonic Equilibrium
Which of the following mixtures will result in a buffer solution with maximum buffer capacity?
Options
- A30 mL of 0.2 M HCOOH + 30 mL of 0.2 M KOH
- B20 mL of 0.2 M HCOOH + 40 mL of 0.2 M KOH
- C40 mL of 0.2 M HCOOH + 20 mL of 0.2 M KOH
- D50 mL of 0.2 M HCOOH + 10 mL of 0.2 M KOH
Correct answer
C. 40 mL of 0.2 M HCOOH + 20 mL of 0.2 M KOH
Step-by-step solution
A buffer solution has maximum buffer capacity when the concentration of the weak acid equals the concentration of its conjugate base (i.e., pH = p K_a ). This requires neutralizing exactly half of the weak acid. Let us calculate the millimoles (mmol) for the mixture in option 3: Initial mmol of HCOOH = 40 mL 0.2 M = 8 mmol Initial mmol of KOH = 20 mL 0.2 M = 4 mmol The neutralization reaction is: HCOOH + KOH HCOOK + H ₂ O Since KOH is the limiting reagent, 4 mmol of KOH will react with 4 mmol of HCOOH to form 4 mmo