Ch.15 - Acid and Base EquilibriumWorksheetSee all chapters
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BONUS: Lab Techniques and Procedures
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Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
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Solution: A solution of 0.23 mol of the chloride salt of protonated quinine (QH+), a weak organic base, in 1.0 L of solution has pH=4.58.Find the Kb of quinine (Q).

Problem

A solution of 0.23 mol of the chloride salt of protonated quinine (QH+), a weak organic base, in 1.0 L of solution has pH=4.58.

Find the Kb of quinine (Q).

Solution

We are being asked to calculate the Kb of quinine (Q)

Quinine chloride salt dissociates into:

QHCl(aq) + H2O(l)→QH+(aq) + Cl-(aq)

Since we’re dealing with a weak acid and Ka is an equilibrium expression, we will have to create an ICE chart to determine the equilibrium concentration of each species:

QH+weak acidproton donor
H2O→ will act as the weak baseproton acceptor


Equilibrium reaction:        QH+(aq) + H2O(l)  Q(aq) + H3O+(aq) 

We are given 0.23 mole of quinine chloride in 1.0 L solution hence:

Molarity(M)=0.23 mol1.0 L

Molarity of QH+ = 0.23 M

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