Strong acid & its conjugate base confusion...

[AlwaysLucky]

In the PR general chem book, page 187, it states the following: "The conjugate base of a strong acid has no basic properties in water"

On the following page, there is a question that asks: "Of the following, which acid has the weakest conjugate base?" A) HClO4, B) HCOOH, C) H3PO4, D) H2CO3

The answer is A. Their reasoning is that because perchloric acid is a strong acid, it will produce a weak conjuate base. BUT how can this be, when the page before states that conjugate bases of strong acids have NO basic properties??? Isn't this contradictory?

Thanks for the help!

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[Jepstein30]

In the PR general chem book, page 187, it states the following: "The conjugate base of a strong acid has no basic properties in water"

On the following page, there is a question that asks: "Of the following, which acid has the weakest conjugate base?" A) HClO4, B) HCOOH, C) H3PO4, D) H2CO3

The answer is A. Their reasoning is that because perchloric acid is a strong acid, it will produce a weak conjuate base. BUT how can this be, when the page before states that conjugate bases of strong acids have NO basic properties??? Isn't this contradictory?

Thanks for the help!

Strong acid = weak conjugate base.

Maybe they were saying previously that the conjugate base of a strong acid is less basic than water (and so in water, it doesn't act as a base?)

 

[orgohacks]

That's how I'd interpret it. Water is a stronger base than the given conjugate base, so that if an acidic proton is around, water will preferentially react with it rather than the specified conjugate base.

 

[AlwaysLucky]

Strong acid = weak conjugate base.

Maybe they were saying previously that the conjugate base of a strong acid is less basic than water (and so in water, it doesn't act as a base?)

Yeah, I recall from my orgo class years ago that strong acid = weak conjugate base ... however, I have no idea why PR would directly claim, verbatim that "conjugate base of a strong acid has no basic properties in water" .... so I guess, because water is more basic than a weak conjugate base, we don't consider a weak conjugate base as a base in water?? 😕 lol

 

[orgohacks]

Strong acid = weak conjugate base.

Maybe they were saying previously that the conjugate base of a strong acid is less basic than water (and so in water, it doesn't act as a base?)

That's how I'd interpret it. Water is a stronger base than the given conjugate base, so that even if a strong acid is present, water will react with it rather than the given conjugate base.

 

[AlwaysLucky]

That's how I'd interpret it. Water is a stronger base than the given conjugate base, so that if an acidic proton is around, water will preferentially react with it rather than the specified conjugate base.

I see .. thanks for the clarification. Also, thanks Jepstein.

 

[LoLCareerGoals]

Ok look, strong is a continuous concept. There is no descrete concept of strong and weak.
When an acid is so strong that it completely dissociates its base is a non-base (or you can call it a very very extremely weak base). When an acid is sort of strong, but does not dissociate completely, then its base is weak (but not super "non base type" weak).

As for the question you posted, you don't even need to understand the concept above to answer it.
Acid that is the strongest in the group has the weakest base. So pick the strongest one. At this point just rely on memorization. (I've memorized top 7 strongest acids/bases for that purpose dunno how others do it).