2009 ADA DAT OC #81

[simplydds]

---

Members do not see this ad.

It asks which is the strongest acid.
They are all carboxylic acids with groups that are involved with induction.

I thought that it would be the carboxylic acid with I since I both electronegative and its size would help stabilize the negative charge.

The answer is the carboxylic acid with the F as the inductive group.
Is this because it's based on how electronegative the atom is?

(F, I, CL, Br, and H are all attached at the same place. ex. F-CH2CO-OH)

Thank you!

 

[dhk2131]

The thing with a carboxylic acid is that deprotonating would place the negative charge on the O, not the I or F or Br like it does in H-I/H-F/H-Br (where H-I is a strong acid since I- is a stable/large anion).

When the negative is on the O, you could stabilize the charge throughout the entire molecule via inductive forces, which solely rely on how electronegative the inductor is, how many there are, and how close they are to the O (or the C connected to the O).

 

[dhk2131]

In other words, you would never get the negative charge literally to be placed on the electronegative inducting atom... since no such resonance form exists. Think about the electronegative atom as just "pulling" the charge in their direction, to disperse it throughout the entire molecule to stabilize the charge.

 

[dhk2131]

:/
this made me nostalgic. i miss studying for the DAT. good luck on yours!

 

[simplydds]

:/
this made me nostalgic. i miss studying for the DAT. good luck on yours!

wow hahah thank you so much!
That makes sense. I- would be a better base than F-. But, like you said, it's all just about the effect it has, thus which atom would pull the most electrons away--F.

And thanks! I need it lol. I'm taking my DAT Sunday.

ps. any chance you know about number 99?

 

[dhk2131]

If that's the weird spasmotol question, then I'm pretty sure that question has a typo... cause the answer they give cannot happen with the reagents of that choice (I wouldn't worry about this question).

 

[dhk2131]

Also, I- would not be a better base than F- (this is something you will see in gen chem). HI is a stronger acid than HF, meaning its conjugate base I- is a weaker base than F-. If you meant better base in terms of being more stable (and thus weaker), that would be correct.

These concepts are VERY important for genchem, as I am sure you will see many questions of the likes (common ion effect/dissociation equations with strong/weak acid/base --> F- will react in water but I- will not etc.).

 

[simplydds]

If that's the weird spasmotol question, then I'm pretty sure that question has a typo... cause the answer they give cannot happen with the reagents of that choice (I wouldn't worry about this question).

that's the one!
haha great. I was like I've never seen anything this complicated on any previous practice tests!

when did you take your dat?
and do you have any last minute tips? haha

 

[dhk2131]

If you mean you are taking the DAT this sunday as in tomorrow, then I would just advise you to do a lot of content review (especially for bio) and do questions from bootcamp/chad's (as many as you can without going insane in order to just keep your mind sharp). Take some breathers as well and try to get a good night's sleep.

Otherwise, if your exam is next sunday/1 week later, do a lot of practice problems. Do destroyer twice, do bootcamp exams twice (should be getting 25+ on each section on second run), do chad's questions etc... with bootcamp, what is helpful is that Ari splits up questions based on topic for each section on the bottom that you can navigate easily.

Good luck!

 

[simplydds]

If you mean you are taking the DAT this sunday as in tomorrow, then I would just advise you to do a lot of content review (especially for bio) and do questions from bootcamp/chad's (as many as you can without going insane in order to just keep your mind sharp). Take some breathers as well and try to get a good night's sleep.

Otherwise, if your exam is next sunday/1 week later, do a lot of practice problems. Do destroyer twice, do bootcamp exams twice (should be getting 25+ on each section on second run), do chad's questions etc... with bootcamp, what is helpful is that Ari splits up questions based on topic for each section on the bottom that you can navigate easily.

Good luck!

Sunday as in this Sunday (10th)
haha good to know! thank you so much! I really appreciate all of your help and advice!

 

[doctorjibbs]

Could anyone help me with Q 76 on the 2009 ADA exam?? My DAT is one week from today and this seems like a really important concept to understand (how charges are distributed on a compound at neutral, acidic, basic pH)!! THANK YOU!!

 

[Pearl E. White]

Could anyone help me with Q 76 on the 2009 ADA exam?? My DAT is one week from today and this seems like a really important concept to understand (how charges are distributed on a compound at neutral, acidic, basic pH)!! THANK YOU!!

This question deals with general amino acid properties and knowledge of pH and pKa. At pH 7, we should recognize this compound should be neutral. This is because the hydroxyl group has a pKa of about 2 and the NH3 group has a pKa of about 9. When the pH>pKa, the functional group is deprotonated. Therefore, the NH3 group will be positively charged, and the hydroxyl group will be deprotonated. Gimmie question. I hope that helped!