The following pictures represent solutions at various stages in the titration of a weak diprotic acid H2A with aqueous NaOH. (Na+ ions and water molecules have been omitted for clarity.)

. (b) Which solution has the highest pH? Which has the lowest pH?

Video transcript

Hello in this problem we are told the diagrams below show the different stages of the temptation of a week. Kaepernick acid H two X with potassium hydroxide for simplicity. Water molecules and potassium ions are not shown. Were asked to identify the solution that has the highest ph and the solution that has lowest ph. So let's begin by drawing a tight rations plot A P. H versus the volume of potassium hydroxide added. So since this is a diaper tick acid, we will have to acidic protons. So we will have to equivalence points. So the first equivalence point then the reaction is taking place. We have our die protic acid reacting with potassium hydroxide. So we're gonna eliminate the potassium mines form the consulate base of our acid and water. So that is shown by the first portion of this situation plot. And then the second portion we have then now our project base reacting with additional hydroxide Form X two and water. And so this then represents the second half of our hydration plot. So if we look at each of the diagrams the first diagram, then one we see that we have well X two minus And we have three drop sides. We have no acid or it's going to be a base. And so we've reached the end of the second equivalent point and now we're just adding additional base and so we'll be around here in our hydration plot. And then diagram to we have our conjugate base present, that's all that's present. We don't have any X two minus or acid or excess hydroxide. So that means we would be at the first equivalence point where we've added then in a face to remove the first acidic proton. Then image three we now have are conjugate base And our acid equal amounts of six. We have no X two or excess hydroxide. So this would be then at the midway point for our first equivalent point, we will be right here. So at this point then we have our acid present and its conjugate base present in equal amounts. And then Diagram four, we have H X minus and X two minus present in equal amounts six. And we have no acid or excess hydroxide. So in this case we would be at halfway point to our second equivalence point. We will be right here at that point. Then we have equal amounts of our conjugate base and X two minus. So looking at our plot, then the highest ph Correspond to Image one. And that's where we are appear in our filtration plot and the lowest ph Correspond to Diagram three, which is indicated by the green point. So our highest ph then is where we have passed the second equivalence point and we've now added excess hydroxide. And so it is excess hydroxide that is determining the ph. And the lowest ph then occurs where we have equal amounts of our acid and its conjugate base. So we are at the midpoint of the first equivalent point. And this corresponds to answer B. Thanks for watching Hope. This helps.