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).

FREE Expert 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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Problem Details

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).

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What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Weak Bases concept. If you need more Weak Bases practice, you can also practice Weak Bases practice problems.