Achieve Question 13

[kiara chan]

In this question, they give me the pKa of a weak acid and the pH. I know that given pH and pKa that pH>pKa in the question, therefore the weak acid is negatively charged. I know that this has to do with the solution's acidity, but can someone explain more specifically how the solutions acidity and the pH being greater than pKa determines the charge?

Thank you!

[Ryan M]

This is a bit of a weird concept, but the idea that I've been using in my head to help sort it all out is that pKa is basically the minimum pH that an acid get 'get' a solution to. If the pH is above pKa, then the acid will 'work,' becoming charged and ionizing the solution. However, if pH is LESS than pKa, then is is obvious that something else is doing the acidification, 'overriding' the weaker acid. In this case, the weaker acid remains neutral and does not become ionized.

In 13, the pH of the solution (6.08) is ABOVE the pKa of the acid (3.67). So, the acid becomes ionized.

Hope that helps!