Consider the titration curves (labeled a and b) for two weak acids, both titrated with 0.100 M NaOH.

(ii) Which acid has the larger Ka?

Video transcript

Hey everyone. So today we're given two different iteration curves of two different weak acids. Let's label this one A and this one be. And both of these weak acids have been tight traded with a strong strong base. So before looking at the anti choice of what the question's asking, let's just point out a couple of key features on this, on these detraction curves. So on graph a we have a tight or an equivalence point right about here, just under a ph of 10. Meanwhile, for acid B, The equivalence point is just at about 10 or maybe slightly above. However, the question is asking us not about the equivalence point, but it's actually asking us about whether acid a has a larger K than acid B or vice versa or if they're the same. And to identify this, we actually need to take a look at the half equivalence points which are here and here, respectively, here and here. So, what these half equivalence points are, they essentially tell us the point at which P k a P k a is equal to the ph of the solution at that point. Or it tells us when at a certain ph that is the P K of the excuse me, the P K of the acid. So just taking a gander here, we can see that the P or the ph at which the Acid B reaches its half equivalence point is sitting at about 7.5. Let's write that. This is sitting at about 7.5, which is equal to PKA. The ph of the solution at that point. And similarly, over here and for acid A. It's sitting more about, let's say 6.2. I'd say that's a good estimate, since the P K. Is lower for acid A. Than for asset B. This therefore means that since P K is just the negative log of the K. A. Then this means that the K A. For acid A is actually larger than acid B, which makes answer choice A. Are correct option. I hope this helps. And I look forward to seeing you all in the next one.