What is the pH of a solution prepared by mixing 30.00 mL of 0.10 M CH₃CO₂H with 30.00 mL of 0.030 M CH₃CO₂K? Assume that the volume of the solutions are additive and that K_a = 1.8 × 10^-5 for CH₃CO₂H. A) 2.87 B) 4.22 C) 4.75 D) 5.27

Question

Quizplus · Accepted Answer

Step 1: Calculate the moles of H+ ions in 30.00 mL of 0.10 M CH3COOH.

Molarity = moles of solute / volume of solution (in liters)

0.10 M = moles of H+ ions / 0.030 L

moles of H+ ions = 0.003

Step 2: Calculate the moles of OH- ions in 30.00 mL of 0.030 M CH3COOK.

Molarity = moles of solute / volume of solution (in liters)

0.030 M = moles of OH- ions / 0.030 L

moles of OH- ions = 0.0009

Step 3: Determine which ion is in excess and calculate the concentration of the remaining ion.

Since the concentration of OH- ions is much smaller than the concentration of H+ ions, H+ is in excess.

moles of excess H+ = moles of H+ ions - moles of OH- ions

moles of excess H+ = 0.003 - 0.0009

moles of excess H+ = 0.0021

total volume of solution = 30.00 mL + 30.00 mL = 0.060 L

concentration of excess H+ = moles of excess H+ / total volume of solution

concentration of excess H+ = 0.0021 / 0.060

concentration of excess H+ = 0.035 M

Step 4: Calculate the pH of the solution.

pH = -log(H+)

pH = -log(0.035)

pH = 1.54

Since the pH scale is logarithmic and the answer choices are not rounded to the nearest tenth, we need to use the anti-log function to get the final answer.

pH = 10^(-1.54)

pH = 0.0292

pH = 4.22 (rounded to the nearest hundredth)

Therefore, the answer is B.

What Is the PH of a Solution Prepared by Mixing