Answer:
pH = 9.08
Explanation:
Quinine, C₂₀H₂₄O₂N₂, Q, is a weak base that, in water, has as equilibrium:
Q + H₂O ⇄ QH⁺ + OH⁻
Where pKb is 5.10
Using H-H equation for weak bases:
pOH = pKb + log₁₀ [QH⁺] / [Q]
The reaction of quinine with HCl is:
Q + HCl → QH⁺ + Cl⁻
Initial moles of quinine are 0.125 moles and moles added of HCl are:
0.05000L × (1.00mol / L) = 0.05000moles.
That means after the addition of 50.00mL of the HCl solution, moles of Q and QH⁺ are:
Q = 0.125mol - 0.050mol = 0.075 moles
QH⁺ = 0.050 moles
Replacing in H-H equation:
pOH = 5.10 + log₁₀ [0.050] / [0.075]
pOH = 4.92
As pH = 14 - pOJ
