Consider the titration of HCl with NaOH. If NaOH is replaced with KOH, the pH of the equivalence point is expected to be:

Question

BlackTom AI · Accepted Answer

Strong acid–strong base titrations give a neutral salt at equivalence, so the equivalence pH is determined by the strengths of the acid and base, not by the identity of the spectator cation.

1) Relevant knowledge points and concepts
- HCl is a strong acid (fully dissociates to H+ and Cl–). NaOH and KOH are both strong bases (fully dissociate to Na+ or K+ and OH–).
- At the equivalence point moles H+ = moles OH–, leaving only water and the salt (NaCl or KCl) in solution.
- Ions derived from strong acids or bases (Cl–, Na+, K+) do not hydrolyze to any significant extent, so they do not change the pH.
- The ideal equivalence pH for a strong acid + strong base titration is pH ≈ 7 (set by water autoprotolysis).

2) Step‑by‑step reasoning
- Neutralization reaction: H+ + OH– → H2O.
- At equivalence, all H+ from HCl has been neutralized by OH– from the base. Remaining species are Cl– (from HCl) and Na+ or K+ (from the base), plus water.
- Cl– is the conjugate base of a strong acid (HCl) and has negligible basicity; Na+ and K+ are cations of strong bases and are non‑acidic spectators.

3) Calculations / intermediate steps
- Stoichiometry: initial moles HCl = moles base added at equivalence.
- [H+] at equilibrium in pure water at 25 °C is 1.0×10^−7 M (pH = 7); since no hydrolyzing ions are present, pH remains ≈7.
- No additional OH– or H+ sources are present from Na+ or K+.

4) Why the correct answer is correct
Because both NaOH and KOH behave as strong monoprotic bases giving identical neutral salts with Cl–, they produce the same non‑hydrolyzing spectator ions; therefore the equivalence point pH is the same.

5) Why other options are incorrect
- “Lower”: would require an acidic salt or residual acid; not true here.
- “Higher”: would require a basic salt (conjugate base hydrolysis) or excess OH–; not true here.

6) Conclusion
The pH at the equivalence point is the same when replacing NaOH with KOH; answer: c. the same.

Consider the titration of HCl with NaOH. If NaOH is replaced with KOH, the pH of the equivalence point is expected to be:单项选择题

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