Answer:
pH = 10.51
Explanation:
The buffer of HCO₃⁻ + CO₃²⁻ has a pka of 10.2
HCO₃⁻ ⇄ H⁺ + CO₃²⁻
0,150L of these substances are:
0,150L × 0,486M NaHCO₃ = 0.0729mol NaHCO₃
0,150L × 0,345M Na₂CO₃ = 0.05175mol Na₂CO₃
NaOH reacts with HCO₃⁻ producing CO₃²⁻, thus:
NaOH + HCO₃⁻ → CO₃²⁻ + H₂O + Na⁺
0.0321 moles of NaOH produce the same moles of CO₃²⁻ and consume HCO₃⁻. Moles of these species are:
CO₃²⁻: 0.05175mol + 0.0321mol: 0.08385mol
HCO₃⁻: 0.0729mol - 0.0321 mol: 0.0408mol
Using Henderson-Hasselbalch formula:
pH = pka + log [Base] / [Acid]
pH = 10.2 + log 0.08385mol / 0.0408mol
pH = 10.51
I hope it helps!
