Calculate the pH of a solution formed by mixing 250.0 mL of 0.15 mol L^-1 HCOOH with 100.0 mL of 0.20 mol L^-1 HCOOLi. The K_a for HCHO₂ is 1.8 × 10^-4. A) 3.87 B) 3.74 C) 10.53 D) 3.47 E) 10.13

Question

Quizplus · Accepted Answer

First, we need to write the balanced chemical equation for the reaction between HCOOH and HCOOLi.
HCOOH + HCOOLi --> LiCOOH + HCOOLi
We can see that the reaction is between a weak acid and its conjugate base. Therefore, it is a buffer solution.
Next, we need to calculate the concentration of HCOOH and HCOOLi after they are mixed.
Initial moles of HCOOH = 0.15 mol/L * 0.250 L = 0.0375 mol
Initial moles of HCOOLi = 0.20 mol/L * 0.100 L = 0.02 mol
Total moles of HCOOH and HCOOLi after they are mixed = 0.0375 mol + 0.02 mol = 0.0575 mol
Total volume after mixing = 250.0 mL + 100.0 mL = 350.0 mL = 0.3500 L
Concentration of HCOOH and HCOOLi after mixing = 0.0575 mol / 0.3500 L = 0.1643 mol/L
Next, we need to calculate the pH using the Henderson-Hasselbalch equation.
pH = pKa + log([A-]/[HA])
where pKa = -log(Ka) = -log(1.8 × 10^-4) = 3.74
[A-] = concentration of HCOOLi = 0.1643 mol/L
[HA] = concentration of HCOOH = 0.1643 mol/L
pH = 3.74 + log(0.1643/0.1643) = 3.74
Therefore, the pH of the solution is 3.74. The best choice is D.

Calculate the PH of a Solution Formed by Mixing 250