GS-2 Physical Sciences Question 8

[rocketbooster]

I chose D, the answer is C according to the answers. A and B are for sure wrong. I knew D didn't look right, but I know C was also wrong so I went with D.

C is wrong because C is a graph of a strong base titrated by a strong acid. Anilene is a weak base. It is not a strong base. Titration curves of weak bases should have a "lip-o-weakness" at the very beginning in which the pH drops immediately because the equilibrium between the weak base and its conjugate acid heavily favors the conjugate acid. After the drop, it then plateaus and continues on.

D is the only answer that may show the lip-o-weakness, but D definitely has far too much of a drop in initial pH and it doesn't show the last plateau at the very end of the titration. I figured maybe the graph just didn't show the entire titration or something and that the 2nd plateau was off the page.

Looking for that lip-o-weakness is the main distinguishing factor between the titration of a weak acid/base and a strong acid/base. Since the tester should know anilene is a weak base, the question should test this knowledge. It doesn't, and well, the question is just completely wrong. It then makes you miss the pH indicator question a few questions later since it bases the answer on the wrong graph. If you happened to pick the "correct" wrong graph, then you get the indicator question right.

Was this never noticed? Is it going to be fixed?

[g.ghepardo6673]

C is the correct titration graph because the equivalence point has a lower pH than 7 (it's around 5). A titration of a strong acid/strong base always has an equivalence point of pH 7.

[ayaz16877372]

Can someone explain this further please. I agree with the OP, I'm pretty confused about why it's not choice D (even though it looked odd with no plateaus at the end, the other curve (choice C) is definitely not a titration of a strong acid with a weak base...

[dnpgr16513]

Can someone please clarify this? Both are obviously wrong. I chose D as well because C is a titration of a strong acid and strong base....................


thanks

[jellywing_2058]

Though answer choice C is the graph for a strong acid and a strong base, it is the best answer, seeing how answer choice D has one plateau as explained in the exam's explanation.