Question

A weak monobasic acid is 10\% dissociated in 0.05 M solution. What is the percent dissociation in 0.15 M solution?

Hint:

To calculate percent dissociation, always use the concentration at which the dissociation constant is given, then solve for the new dissociation at the target concentration using the relationship between \(K_a\) and concentration.

Answer 1

Step 1: Use the formula for dissociation.
The dissociation of a weak acid is governed by the equation: \[ \alpha = \sqrt{\frac{K_a \cdot C}{1 + \alpha}} \] Where \(K_a\) is the dissociation constant, \(C\) is the concentration of the acid, and \(\alpha\) is the degree of dissociation. Step 2: Given information.
The acid is 10\% dissociated at 0.05 M, so we can use this to calculate \(K_a\). \[ \alpha = \frac{10}{100} = 0.1 \] Now we can substitute into the dissociation equation to find the value of \(K_a\). Once \(K_a\) is calculated, use it to determine the dissociation at 0.15 M by substituting into the dissociation equation again.