Chemistry Practice Problems Weak Bases Practice Problems Solution: The pH of 0.1 M C 4H9NH2(aq) (butylamine) aqueous ...

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Solution: The pH of 0.1 M C 4H9NH2(aq) (butylamine) aqueous solution was measured to be 12.04. What is the value of pKb of butylamine?1. 1.962. 2.933. 2.574. 0.255. 3.506. 2.87

Problem

The pH of 0.1 M C 4H9NH2(aq) (butylamine) aqueous solution was measured to be 12.04. What is the value of pKb of butylamine?

1. 1.96

2. 2.93

3. 2.57

4. 0.25

5. 3.50

6. 2.87

Solution

We are being asked to calculate the pKb for a 0.1 M solution of C4H9NH2 (butylamine). 

C4H9NH2 (butylamine) is a neutral amine, therefore we know that it is a weak base.


We can calculate the pKb of butylamine from its Kb using the following equation:

pKb=-log Kb


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

C4H9NH2weak baseproton acceptor
H2O → will act as the weak acidproton donor


Equilibrium reaction:        C4H9NH2(aq) + H2O(l)  C4H9NH3+(aq) + OH-(aq)

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