Question

Which has the larger numerical value? (a) The \(\mathrm{p} K_{\mathrm{a}}\) of a strong acid or the \(\mathrm{p} K_{\mathrm{a}}\) of a weak acid (b) The \(K_{\mathrm{a}}\) of a strong acid or the \(K_{\mathrm{a}}\) of a weak acid

Short answer

Question: Compare the pKa and Ka values of strong and weak acids. Answer: The pKa of a weak acid has a larger numerical value, while the Ka of a strong acid has a larger numerical value.

Step-by-step solution

Defining strong and weak acids

A strong acid is an acid that completely dissociates in water, while a weak acid is an acid that dissociates partially in water. In other words, strong acids have a greater tendency to donate a proton (H+) to a solution than weak acids, making the resulting solution more acidic.

Understanding pKa and Ka values

The Ka value, also known as the acid dissociation constant, is a measure of the strength of an acid in a solution. The larger the Ka value, the stronger the acid. On the other hand, the pKa value is the negative logarithm of the Ka value (pKa = -log(Ka)). Therefore, the smaller the pKa value, the stronger the acid. (a)

Comparing pKa values for strong and weak acids

Since strong acids have larger Ka values, their corresponding pKa values would be smaller (due to the negative logarithm). Therefore, the pKa of a strong acid is smaller than the pKa of a weak acid. So, the weak acid has a larger numerical value for pKa. (b)

Comparing Ka values for strong and weak acids

By definition, a strong acid has a larger Ka value than a weak acid. So, the Ka of a strong acid is larger than the Ka of a weak acid. In conclusion: (a) The pKa of a weak acid has a larger numerical value. (b) The Ka of a strong acid has a larger numerical value.