Question

Consider the titration of 50.0 ml of 0.0500 m nh3 (a weak base; kb = 1.80e-05) with 0.100 m hclo4. calculate the ph after the following volumes of titrant have been added: (a) 0.0 ml ph = (b) 6.3 ml ph = (c) 12.5 ml ph = (d) 18.8 ml ph = (e) 25.0 ml ph = (f) 35.0 ml ph =

Answer 1

Calculating pH during the titration of a weak base with a strong acid requires a step-by-step approach to determine the pH at different points including the initial pH, before and after the equivalence point by considering the equilibrium expressions and known Ka or Kb values.

Step-by-step explanation:

The titration of a weak base (NH3) with a strong acid (HClO4) involves various pH calculations at different stages of the titration process. A systematic approach to such a titration problem includes calculating the pH at the start (with only NH3 present), at intermediate points (mixture of NH3 and NH4+), at the equivalence point, and beyond the equivalence point (excess HClO4).

For instance, at the start (0.0 mL of HClO4 added), the pH is calculated based solely on the dissociation of NH3 in water. As HClO4 is added, NH3 is neutralized to form NH4+, thus decreasing the pH. Approaching the equivalence point, the acid-base neutralization reaction is complete, and the pH depends on the NH4+ ion, which slightly dissociates in water. Finally, upon adding an excess of HClO4, the pH is dictated by the concentration of the excess strong acid.

Steps for Calculating pH During a Titration:

1. Calculate initial pH using only the weak base or acid present.
2. Calculate the amounts of acid and base that have reacted to determine the concentration of the species present in the solution.
3. Use the equilibrium expressions and known Ka or Kb values to calculate [H+] or [OH-].
4. Calculate the pH from [H+] or [OH-] as appropriate.