The pH at the equivalence point in the titration of the hydrofluoric acid (HF) solution with sodium hydroxide (NaOH) is approximately 7.
At the equivalence point, the moles of acid (HF) equal the moles of base (NaOH), leading to the formation of water and sodium fluoride (NaF). The balanced equation is:
HF + NaOH — NaF + H₂O
Sodium fluoride is a salt, and its aqueous solution undergoes hydrolysis. The fluoride ion (F⁻) reacts with water to form hydrofluoric acid (HF) and hydroxide ions (OH⁻):
F⁻ + H₂O ⇌HF + OH⁻
The hydrolysis of sodium fluoride results in the production of hydroxide ions, causing the solution to be slightly basic. The pH at the equivalence point is around 7, indicating neutrality.
In summary, the pH at the equivalence point is approximately 7 due to the hydrolysis of the salt formed from the neutralization reaction, resulting in a slightly basic solution.