Chemistry Practice Problems Weak Bases Practice Problems Solution: Aniline, C6H5NH2, is a weak base that dissociates ...

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Solution: Aniline, C6H5NH2, is a weak base that dissociates in water. At 25 °Celsius, the base dissociation constant, Kb , for aniline is 4.3 x 10 -10.(A) Determine the hydroxide ion concentration and the percentage dissociation of a 0.150 molar solution of aniline at 25 °Celsius.

Problem

Aniline, C6H5NH2, is a weak base that dissociates in water. At 25 °Celsius, the base dissociation constant, K, for aniline is 4.3 x 10 -10.

(A) Determine the hydroxide ion concentration and the percentage dissociation of a 0.150 molar solution of aniline at 25 °Celsius.

Solution

We’re being asked to calculate the equilibrium concentration of the hydroxide ion (OH-) in a 0.150 M C6H5NH2 solution.


To solve this problem, we need to:

Step 1. Determine the dissociation of the base in water.

Step 2. Construct the ICE chart.

Step 3. Determine the equilibrium concentration of OH-



Step 1Since C6H5NH2 has a low Kb value, it’s a weak base. Remember that weak bases partially dissociate in water and that bases accept H+ from the acid (water in this case). The dissociation of  C6H5NH2 is as follows:

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