Question

Question- In the titration of a weak acid with a strong base, how would you calculate these quantities?

Multiple choice

Part A

initial pH

a. The initial pH is that of the strong base solution use for titration. Calculate the pH by working an equilibrium problem using the concentration of the weak acid as the initial concentration

b.The initial pH is that of the weak acid solution to be titrated. Calculate the pH by working an equilibrium problem using the concentration of the strong base as the initial concentration.

c.The initial pH is that of the strong base solution to be titrated. Calculate the pH by working an equilibrium problem using the concentration of the strong base as the initial concentration.

d. The initial pH is that of the weak acid solution to be titrated. Calculate the pH by working an equilibrium problem using the concentration of the weak acid as the initial concentration.

Part B

pH before the equivalence point

a. Between the initial pH and the equivalence point, the solution becomes a base. Use the reaction stoichiometry to compute the amounts of each buffer component and then use the Henderson–Hasselbalch equation to compute the pH.

b. Between the initial pH and the equivalence point, the solution becomes a buffer. Use the reaction stoichiometry to compute the amounts of each buffer component and then use the Henderson–Hasselbalch equation to compute the pH.

c. Between the initial pH and the equivalence point, the solution becomes a buffer. Calculate the pH by working an equilibrium problem using the concentration of the weak acid as the initial concentration.

d. Between the initial pH and the equivalence point, the solution becomes an acid. Use the reaction stoichiometry to compute the amounts of each buffer component and then use the Henderson–Hasselbalch equation to compute the pH.

Part C

pH at one-half the equivalence point

a.Halfway to the equivalence point, the buffer components are exactly equal and pH = pKa.

b. Halfway to the equivalence point, the buffer components are nearly equal and pH is approximately pKa.

Part D

pH at the equivalence point

a. At the equivalence point, the acid has all been converted into its conjugate base. Calculate the pH by working an equilibrium problem for the ionization of water by the ion acting as a weak base. (Compute the concentration of the ion acting as a weak base by dividing the number of moles of the ion by the total volume at the equivalence point.)

b. At the equivalence point, the acid has all been converted into its conjugate base. Calculate the pH by working an equilibrium problem for the ionization of water by the ion acting as a weak acid. (Compute the concentration of the ion acting as a weak acid by dividing the number of moles of the ion by the total volume at the equivalence point.)

c. At the equivalence point, the base has all been converted into its conjugate acid. Calculate the pH by working an equilibrium problem for the ionization of water by the ion acting as a weak base. (Compute the concentration of the ion acting as a weak base by dividing the number of moles of the ion by the total volume at the equivalence point.)

d. At the equivalence point, the acid has all been converted into its conjugate base. Calculate the pH by working an equilibrium problem for the ionization of water by the ion acting as a weak acid. (Compute the concentration of the ion acting as a weak acid by dividing the number of moles of the ion by the total volume at the base.)

Part E

pH beyond the equivalence point

a.Beyond the equivalence point, H3O+ is in excess. You can ignore the weak base and calculate the [OH−] by subtracting the initial number of moles of H3O+ from the number of moles of added OH− and dividing by the total volume, then converting to pH using -log[H3O+].

b. Beyond the equivalence point, H3O+ is in excess. You can ignore the weak base and calculate the [OH−] by subtracting the initial number of moles of H3O+ from the number of moles of added OH− and dividing by the total volume, then converting to pH using -log[OH−].

c. Beyond the equivalence point, OH− is in excess. You can ignore the weak base and calculate the [OH−] by subtracting the initial number of moles of H3O+ from the number of moles of added OH− and dividing by the total volume, then converting to pH using -log[OH−].

d. Beyond the equivalence point, OH− is in excess. You can ignore the weak base and calculate the [OH−] by subtracting the initial number of moles of H3O+ from the number of moles of added OH− and dividing by the total volume, then converting to pH using -log[H3O+].