Question

When 50 mL of 0.40 M hydrofluoric acid and 50 mL of 0.40 M potassium hydroxide are combined, the pH of the resulting solution will be

A. Less than 7
B. Equal to 7
C. Greater than 7

Answer 1

The pH of the resulting solution when equal volumes and molarities of 0.40 M hydrofluoric acid and 0.40 M potassium hydroxide are mixed is neutral, with a pH equal to 7.

Step-by-step explanation:

When 50 mL of 0.40 M hydrofluoric acid (HF) is combined with 50 mL of 0.40 M potassium hydroxide (KOH), a neutralization reaction occurs. Both solutions have the same molarity and volume, so they will neutralize each other. The resulting solution will have a pH equal to 7, which is neutral at 25 °C. The hydrofluoric acid provides hydronium ions (H3O+), while potassium hydroxide provides hydroxide ions (OH−). When these are combined in equal molar amounts, they form water and a salt (in this case, potassium fluoride, KF), and the pH of the resulting solution is 7, assuming complete dissociation of both the acid and the base.

This can be understood by knowing that, at 25 °C, neutral water has a hydronium ion concentration and a hydroxide ion concentration of 1.0 × 10−7 M. The pH is calculated using the formula pH = -log[H3O+] and the pOH using the formula pOH = -log[OH−]. Since the acid and base neutralize each other, their ionic contributions to the solution's pH balance out, resulting in a neutral pH 7.