Problem: Determine the pH of each of the following two-component solutions.6.00×10−2 M in HI and 8.50×10−3 M in HF

We are being asked to determine the pH of the following two-component solution: 

6.00 × 10⁻² M in HI and 8.50 × 10⁻³ M in HF

Recall that the pH and pOH of a compound determine its acidity and basicity.

• pH

▪ pH stands for the negative logarithmic function of hydronium ion concentration
▪ can be calculated using the following equation:

$\boxed{\mathbf{pH}\mathbf{=}\mathbf{-}\mathbf{log}\mathbf{ }\left[{\mathbf{H}}^{\mathbf{+}}\right]}$

Take note that:         [H⁺] = [H₃O⁺]

Remember that:

• HI is a strong acid → completely dissociates in solution:
  • HI → H⁺ + I^-
    • [HI] = [H⁺]
• HF is a weak acid  → partially dissociates in solution:
  • HI ⇋ H⁺ + F^-
    • [HF] > [H⁺]

This means that for this mixture, the pH will depend on the concentration of the strong acid, HI: