Questions 4-6 pertain to this titration curve A weak monoprotic acid is titrated with a
strong base, KOH. A titration curve typically has the volume
of the titrant, usually a strong base, on the x axis, and the resulting pH on the y
axis. There’s an equivalence point on the graph
where all of the starting solution has been neutralized by the titrant. So here we started
with an acid, and it’s the point where you’ve added enough base to neutralize the acid.
You can usually eyeball this point - where the concavity of the graph changes .
The point at which the moles of the added strong base are equal to the moles of the
weak acid initially present.
The answer is C, that's what we were just talking about.
You can see where the concavity of the graph changes.
This is the equivalence point.
And you can see on the graph it corresponds with about 100 mL of KOH
The point at which the pH is closest to that of the strong base being added
This is point E. We are past the equivalence point, where all the acid has been neutralized.
Past that point, more and more base is being added, so you can see the pH increasing and
increasing, until it starts to level off. You can see it is still changing at point
D, so it’s not quite at the pH of the titrant. But by point E, the curve is changing less
and is closer to a plateau. So E is the best answer.
The point at which the concentrations of the weak acid and its conjugate base are approximately equal.
So here you need to know a little detail about titration curves.
For monoprotic acids, the point halfway
between the start of the curve and the equivalence point is significant - that’s where the
concentrations of the acid and its conjugate base are equal. We found the equivalence point
was C, when you add 100 mL of KOH. Halfway is 50 mL, which corresponds to point B on
the graph.
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