Answer:
pH = 7,0
Explanation:
The buffer producing by the mixture of H₂PO₄⁻ and HPO₄²⁻ is:
H₂PO₄⁻ ⇄ HPO₄²⁻ + H⁺; pka: 7,21
Using the Henderson-Hasselbalch formula:
pH = pka + log₁₀ A⁻ / HA
Where: A⁻ is the conjugate base (HPO₄²⁻) and HA is the weak acid (H₂PO₄⁻)
Replacing the formula:
pH = 7,21 + log₁₀ HPO₄²⁻ / H₂PO₄⁻
As the moles of HPO₄²⁻ are 0,0966 and moles of H₂PO₄⁻ are 0,157:
pH = 7,21 + log₁₀ 0,0966 / 0,157
pH = 7,0
I hope it helps!
