Chemistry Practice Exam 1 Discussion

[stonecold]

Has anyone done it?
What did you think of it?

For me, its been by far the best prac exam i've done so far.
Don't know whether that just means it was easy or if I'm actually improving haha!

But I still have a few questions.

Can someone please explain multi choice questions 10 and 15.

Also with short answer question 2, the answers should be in two sig figs yeah?   The question only says 1.5g, yet the answers give three sig figs...

And with question 6, is phenol a functional group in salycilic acid?  i.e. the benzene ring?

Thanks.

[azn_dj]

I would argue that Phenol is a functional group.

I doubt the answer to Question 11. The answer should be C, not A.

Question 5Bi - Sooo freakin ambiguous! I really doubt this will be on a real exam.

[stonecold]

Nah, 11 is definitely A dj.

And 5.bi was okay too.  I just forgot to mention the PCR...

Instead I said denaturation, annealation and elongation...

[azn_dj]

Explain 11 then.
My logic is because its next to ANY hydrogen in an ajoining carbon, it will cause splitting.
Just because they are equivalent, I dont think this would change splitting patterns.

[stonecold]

Ahhh, I get where you are coming from.  I dunno, maybe it does effect the peak splitting...

It is called 1,2-dihydroxyethane.  Can anyone find the NRM NMR spectrum?

[azn_dj]

I believe its an NMR spectrum. Not an NRM =P
Currently installing chemical detectives. I thought it was already on my computer, but apparently its not.
Will get spectrum of it soon.

[stonecold]

lol, nrm...how lame.  that would be great. at least we can get the real answer

where do you get the program from may I ask?

dw, its sweet, i found it

[fady_22]

Phenol is not just the benzene ring, but also contains the hydroxyl group.
Multi 10: Choose the strongest base!

Question 15 can be answered by elimination. B and C are obviously wrong (ethane cannot react to form an amine) and the reaction with ethanol requires a catalyst such as alumina, making D wrong. Therefore A is correct.

[stonecold]

^ back to learning my reactions mind map properly

I get that the SO4 and NO3 are acids, but how do you know NH4+ is weaker than CO3?

[fady_22]

^ back to learning my reactions mind map properly

I get that the SO4 and NO3 are acids, but how do you know NH4+ is weaker than CO3?

Sodium sulfate and sodium nitrate are not acids. And NH4+ is an acid, not a base.

[stonecold]

^ back to learning my reactions mind map properly

I get that the SO4 and NO3 are acids, but how do you know NH4+ is weaker than CO3?

Sodium sulfate and sodium nitrate are not acids. And NH4+ is an acid, not a base.

Aaargh I'm all confused now.  How do you what is an acid or a base if there is no H+ or OH- present.
Sorry, I've never been taught this stuff.

edit: And why am I only installing this Chem Detective stuff now!  I could have used this for the past 3 months whilst I haven't been understanding all this spectroscopic stuff.  ah well, better late than never...

edit 2: umm, maybe you don't get the peak splitting because the molecule is symmetrical, and the proton environments are the same, so the interference from each of the H+ environments cancel each other out...

[fady_22]

^ back to learning my reactions mind map properly

I get that the SO4 and NO3 are acids, but how do you know NH4+ is weaker than CO3?

Sodium sulfate and sodium nitrate are not acids. And NH4+ is an acid, not a base.

Aaargh I'm all confused now.  How do you what is an acid or a base if there is no H+ or OH- present.
Sorry, I've never been taught this stuff.

That's OK. I'll (try to) explain.
NH4+ is an acid because it has the ability to donate a proton to become NH3.
Metal Carbonates able to accept a proton, and can react with acids to form a salt, carbon dioxide and water.
Nitrates and sulfates are weak bases (conjugates of strong acids).

[fady_22]

Also, OH groups do not cause peak splitting "for reasons beyond the scope of the course".

[olly_s15]

NH4+ readily donates a proton to become the more stable NH3 and hence can act as an acid. Correct me if I'm wrong.

[azn_dj]

fady_22: Not beyond the course - splitting only occurs if atoms are 3 away.
H to the O to the C. thats it. BUT will cause a peak if its water because its H to the O to the H.
[IMG]http://img683.imageshack.us/img683/1637/ethandiol.th.png[/img]


Admittedly I was wrong. But can someone explain the chemistry behind this?