Strength in Basicity (Destroyer 2010)

[calicarbocation]

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Between HClO4 and ClO4-, the destroyer says that ClO4- is a weaker base in water.

I thought that weaker bases would make stronger acids. And don't acids donate protons most readily? Well ClO4- doesn't even have any protons to donate in the first place. If anything it seems like it would accept a proton, making it seem more basic.

If you were just looking at them as answer choices and didn't have the time to draw out the molecules to see the structures/distribution of electrons, how would you know that ClO4- is weaker base than HClO4?

 

[MobiusStrip]

It is because the negative charge can be delocalized over the oxygen reducing the need for it to accept a proton making it a weaker base (proton acceptor)

 

[MobiusStrip]

Another way of looking at it is that as the oxidation increases so does the strength of the Cl-O bond which will weaken the -OH bond of the conjugate acid do to EW. This will make the the conj acid stronger and the base weaker. Hope this helps.

 

[Skateguitar]

HClO4 = Strong Acid, so
Strong Acid = Weak Conj Base?

 

[calicarbocation]

It is because the negative charge can be delocalized over the oxygen reducing the need for it to accept a proton making it a weaker base (proton acceptor)

I think I see what you're saying. The electrons in ClO4- are delocalized among 3 triple bonds and one single bond along with the negative charge on one oxygen. It's got a nice resonance/stablized thing going on. However, in HClO4, all that has to happen is that it would loose an H to obtain that same state of stability. So wouldn't HClO4 be really likely to want to give up that proton attached to oxygen? If so, then that would be acidic behavior, which would mean less basic. You know what I mean?

 

[MobiusStrip]

HClO4 = Strong Acid, so
Strong Acid = Weak Conj Base?

Right.

 

[MobiusStrip]

I think I see what you're saying. The electrons in ClO4- are delocalized among 3 triple bonds and one single bond along with the negative charge on one oxygen. It's got a nice resonance/stablized thing going on. However, in HClO4, all that has to happen is that it would loose an H to obtain that same state of stability. So wouldn't HClO4 be really likely to want to give up that proton attached to oxygen? If so, then that would be acidic behavior, which would mean less basic. You know what I mean?

Sorry... I might be misunderstanding you. If it gives up an H it wont be HClO4 anymore rather ClO4-, Which is a weak base.

 

[Thundercatz]

You should know the 7 strong acids: HCl, HBr, HI, HNO3, H2SO4, HClO4, and HClO3.

HClO4 --> H+ + ClO4-

HClO4 is a strong acid
ClO4- is its conjugate base

A conjugate base of a strong acid is a weak base.

 

[MobiusStrip]

The structure looks like this....

 

[calicarbocation]

Thank you guys. That helped a lot...HClO4's conjugate base is going to be very weak since it's such a strong acid. It wouldn't make sense if HClO4 was a weak base, I don't know why I got so confused

 

[MobiusStrip]

You should know the 7 strong acids: HCl, HBr, HI, HNO3, H2SO4, HClO4, and HClO3.

HClO4 --> H+ + ClO4-

HClO4 is a strong acid
ClO4- is its conjugate base

A conjugate base of a strong acid is a weak base.

Def a good plan to know all of the the strong inorganic acids here. Also you might wanna know the strong organic acids as well like tosylate benzoic acid , etc.
Other than that you should be good, you def wont need to know any of the super acids like antimony pentafluoride etc.

 

[calicarbocation]

I just took the third test and wasn't too pleased with my score....everybody says your scored improve on the actual DAT, but by how much can I expect it to improve?! 2 points? more? Kinda worried here....😕

 

[MobiusStrip]

Plan on not using that as a train of thought... best to plan on it being redic and over preparing then shootin of a bunch of 15 on practice exams with the idea that the real thing will be easier. Its so subjective and depends on what version you get on test day... some are easier then others.
In gen thought topscorer achiever and destroyer seem to all have their areas which are more demanding then the actually DAT itself. If you look throught the forum they have a lot of comparisons.

 

[DQLEUCD]

Between HClO4 and ClO4-, the destroyer says that ClO4- is a weaker base in water.

I thought that weaker bases would make stronger acids. And don't acids donate protons most readily? Well ClO4- doesn't even have any protons to donate in the first place. If anything it seems like it would accept a proton, making it seem more basic.

If you were just looking at them as answer choices and didn't have the time to draw out the molecules to see the structures/distribution of electrons, how would you know that ClO4- is weaker base than HClO4?

The question seems like which is the weaker base. Since ClO4- is an ion, it can be stabilized through resonance because of it's charge and also you have water, which is a protic solvent that's also stabilizing it making it an even more weaker base then the conjugate base HClO4.

 

[rmm30]

still dont get it. im aware that the conj base of a strong acid is weak base but that doesn't say anything about the bascity of HClO4. i also understand that basicity decreases with the ability to delocalize charge through resonance. BUT i also know that the strength of the base INCREASES with charge (see OH- > H20 , NH2- > NH3). So by this measure CLO4- would be the stronger base.

Also if you measure base strength as the ability to donate electons (Lewis def) or ability to accomadate a proton then it seems ClO4- is a stronger (but weak base none the less) base than HClO4 (another weak base). Could somebody please explan?

 

[rav4182]

an easier way to think of it is:

If you want to find the stronger/weaker acid/base

Just look for the one with the weaker/stronger conjugate base/acid

 

[rmm30]

an easier way to think of it is:

If you want to find the stronger/weaker acid/base

Just look for the one with the weaker/stronger conjugate base/acid

could you briefly explain using HClO4 and ClO4- as an example? What about H2SO4 and HSO4-? I dont see how this logic applies to these two situations. If you want to find the weaker base between NH3 and Cl-, you could look at the conjugate acid of each (NH4+ and HCl respectively) and guage base strengh accordingly. But how does this method work with HClO4 and ClO4-? thanks

 

[rmm30]

Thank you guys. That helped a lot...HClO4's conjugate base is going to be very weak since it's such a strong acid. It wouldn't make sense if HClO4 was a weak base, I don't know why I got so confused

HClO4 IS a weak base.

 

[Jia7]

HClO4 IS a weak base.

HClO4 is a strong acid. It's conjugate base ClO4- is a very weak base.

 

[rmm30]

HClO4 is a strong acid. It's conjugate base ClO4- is a very weak base.

HClO4 is a strong acid. And a weak base. H20 is also a weak base. So is H2SO4. so are other species that have lone electron pairs to donate to electrophilic carbon. Thats why you cant evaluate this problem based on conj. acid/base strengths. What is the conjugate acid of HClO4? probably would be far to unstable to even exist.