Destroer Genchem #135

[athomas]

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I am wondering why A isn't the right answer. The question just says weakest base, not weakest conjugate base. I feel like the explanation and answer choice E would work if it asked for conjugate base, since ClO4- is the CB of the strongest acid on the list, but just 'weakest base' to me seems like it should be HClO4 since it's so acidic and definitely not going to act as a base (whereas ClO4- has more basicity, however small).

Picture won't upload so here is relevant part :/

Which of the following is the weakest base?
A) HClO4
B) NH3
C) NH2-
D) OH-
D) ClO4-

Answer E "The weakest base comes frome the strongest acid. A is wrong; it is a strong mineral acid called perchloric acid...ClO4- came from HClO4, thus ClO4- is the weaker base" (comp to N
3)

 

[Moka11]

I am wondering why A isn't the right answer. The question just says weakest base, not weakest conjugate base. I feel like the explanation and answer choice E would work if it asked for conjugate base, since ClO4- is the CB of the strongest acid on the list, but just 'weakest base' to me seems like it should be HClO4 since it's so acidic and definitely not going to act as a base (whereas ClO4- has more basicity, however small).

Picture won't upload so here is relevant part :/

Which of the following is the weakest base?
A) HClO4
B) NH3
C) NH2-
D) OH-
E) ClO4-

Answer E "The weakest base comes frome the strongest acid. A is wrong; it is a strong mineral acid called perchloric acid...ClO4- came from HClO4, thus ClO4- is the weaker base" (comp to N
3)

I messed up on that too my first time through.
HClO4 does nothing that would make it a base. Its an acid not a base. The conjugate acid H2ClO4 doesnt exist under normal conditions.

 

[athomas]

Right...so wouldn't that make it weakest since it will never act as a base? I understand why A would be wrong if it asked for weakest conjugate base (since it has no conjugate acid).

I also see how A would be wrong if it said something like which of these is the weakest base that will still deprotonate water to some extent (or something more concise haha). Like which if these is the least basic but STILL IS a base. The way the question is written seems to me like they are looking for the least basic compound irrespective of whether it is actually a base.