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

(b)

(ii) Which base has the larger Kb?

Video transcript

Hey everyone today, we're given two different taxation curves of two different weak bases A and B. A and B. That have been tight rated with a strong acid. And we're being asked based on the situation curves which of the following statements are true. So let's go ahead and start and look with the first one where it states that base A has a smaller KB than base B. So when we're dealing with KB, we need to know that when we're tight trading a strong asset into a week based solution, there is a point at which the P K B will be equal to the ph And this point is at the half equivalence point. Now the equivalence point and I'll draw this in red will be where you see the steep change in ph so it'll be here and here half that point. The half the government's point is where the ph is equal to the PKB. Let's write this in blue. So that will fall somewhere around here. For or for base A somewhere about here for base B. Now remember we are working with weak acids that are being treated with a strong or weak bases that are being treated with a strong acid. Now, if we look just at acid A alone or base A alone when it's being titrate. Id the ph at which it reaches. But the ph at which we reached, the half equivalence point is far higher than the ph of which the half equivalence point is reached in base B. It is at a ph of about 9.8. Whereas let's write that, it's about 9.8. Whereas the equivalence point is only reached at a ph of about seven and neutral ph in base B. This means that the PKB must end. Therefore, the KB of Base A must be far greater than Base B, which means this is false. And because of that same logic, that also means that answer choice B must be true. We just established that Base B has a smaller PKB and therefore a smaller KB. Then base A. Due to the fact that the volume at which the or the ph at which the volume that the half equivalence point is reached is far lower. I hope this helps. And I look forward to seeing you all in the next one.