DAT Destroyer gen chem #182

[GoGreenAndFloss]

Which is false?
a) HBrO4 is stronger acid than HBrO2
b) P4O10 is an acidic oxide
c) HF contains the most electronegative element, thus HF will ionize 100%
d) I- is a weak base
e) All of these are true


I understand why the answer to this is C, however I was under the impression that the conjugate base of strong acids such as HI can't even be considered a base since they are so stable. So moving forward should I consider conjugate bases of a strong acid a weak base? When a question asks something like how is pH affected by NaI the answer would be no affect, correct? So doesn't that mean I- can't even be considered a base?

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[Syxx]

Yes, the conjugate base of a strong acid is a weak base. When simply trying to identify something as an acid/base/conjugate acid/conjugate base
rely on the definitions.

I- can be defined to be a Lewis base because a Lewis base is anything that can donate a pair on nonbonding electrons.
One organic chemistry reaction you need to be familiar with for the DAT is the reaction of an alcohol with H-X to form an alkyl halide.
I- in that reaction from H-I acts as a Lewis base.

For the purposes of the DAT, you can assume that putting a salt that forms from the reaction of a strong acid and
strong base in water will not change the pH. These salts will not undergo hydrolysis with water.

_________________________________________

I will mention in real life it's more complicated, especially if your solution is not neutral. So if ever in a lab setting,
and you have an acidic or basic solution, don't be suprised if addition of NaCl/NaI/etc alters the pH. Terms like
activity coefficients and ionic strength which are taught in pchem or chemical thermodynamics courses are coming into play
in that situation.

 

[GoGreenAndFloss]

Yes, the conjugate base of a strong acid is a weak base. When simply trying to identify something as an acid/base/conjugate acid/conjugate base
rely on the definitions.

I- can be defined to be a Lewis base because a Lewis base is anything that can donate a pair on nonbonding electrons.
One organic chemistry reaction you need to be familiar with for the DAT is the reaction of an alcohol with H-X to form an alkyl halide.
I- in that reaction from H-I acts as a Lewis base.

For the purposes of the DAT, you can assume that putting a salt that forms from the reaction of a strong acid and
strong base in water will not change the pH. These salts will not undergo hydrolysis with water.

_________________________________________

I will mention in real life it's more complicated, especially if your solution is not neutral. So if ever in a lab setting,
and you have an acidic or basic solution, don't be suprised if addition of NaCl/NaI/etc alters the pH. Terms like
activity coefficients and ionic strength which are taught in pchem or chemical thermodynamics courses are coming into play
in that situation.

Thanks! I kind of figured that was the case but needed a little extra clarification. I appreciate the extra details.