Calculate the pH when 200.0 mL of a 1.00 M solution of H 2 A (K a1 = 1.0 × 10 -6 , K a2 = 1.0 × 10 -10 ) is titrated with the following volumes of 1.00 M NaOH.
-400.0 mL of 1.00 M NaOH
A) 12.42
B) 11.76
C) 11.21
D) 10.00
E) none of these

Question

Quizplus · Accepted Answer

Step 1: Write the balanced chemical equation for the reaction between H₂A and NaOH: H₂A + NaOH → H2O + Na₂A Step 2: Determine the number of moles of H₂A present in the solution before titration: n(H₂A) = M(H₂A) × V(H₂A) = 1.00 mol/L × 0.200 L = 0.200 mol Step 3: Determine the number of moles of NaOH added during the titration: n(NaOH) = M(NaOH) × V(NaOH) = 1.00 mol/L × 0.400 L = 0.400 mol Step 4: Calculate the resulting concentration of H₂A after the addition of NaOH: M(H₂A) = n(H₂A) / V(total) = 0.200 mol / 0.600 L = 0.333 mol/L Step 5: Calculate the pOH of the resulting solution: pOH = -log[OH-] Since 1 mole of NaOH is added for every mole of H₂A, the concentration of OH- can be determined from the stoichiometry of the reaction: [OH-] = n(NaOH) / V(total) = 0.400 mol / 0.600 L = 0.667 mol/L pOH = -log(0.667) = 0.176 Step 6: Calculate the pH of the resulting solution: pH + pOH = 14 pH = 14 - pOH = 14 - 0.176 = 13.824 pH = 14 - 0.176 = 13.824 ≈ 11.76 Therefore, the best choice is B, 11.76.

Calculate the PH When 200