Final answer:
The pH at the equivalence point in the titration of NH3, a weak base, with a strong acid is acidic because the reaction produces a weak acid that lowers the pH below 7.
Step-by-step explanation:
When titrating NH3, a weak base, with a strong acid, the pH at the equivalence point is expected to be acidic. This is because the reaction produces the conjugate acid of the weak base, which can then release protons (H+) into the solution, causing the pH to drop below 7. The strength of the weak base as indicated by its pKb value and the concentration of the solutions can affect the exact pH at the equivalence point, but it will remain on the acidic side for NH3.