A chemistry problem about molecular formula

[iLoveDivX]

I just took a chem test and there was a problem that was worth a lot of point (8% of the test) that I wasn't sure about. The results will be out tomorrow, but i'm just anxious to know what it is.

Caffeine is 49.47% C, 5.19% H, 28.86% N, and 16.48% O. If the molecular mass of caffeine is 207 g mol, what is the molecular formula?

A. C4H5O (All of the numbers are subscript btw)
B. C8H10O2
C. C12H15O3
D. None of the Above

I put the answer is C. But there was nitrogen in the description of caffeine but the answers didn't have nitrogen in it. So i wasn't sure if he accidentally left it out or if it is a trick question or if nitrogen is always left out in the formula of caffeine. There are 25 questions on this test and a total of 100 points. This problem is the only one that's worth 8 points (all of the other ones are 4 a piece), that's why i figured that a college professor wouldn't be childish enough to put a trick question especially on a problem that's worth the most points.

Anyone know for SURE what the answer is?

 

[iamwiz82]

can you give me the molecular weights of each element?

 

[iLoveDivX]

Carbon- 12
Hydrogen - 1
Nitrogen - 14
Oxygen - 16

 

[Robert01]

molecular weight:
C : 12.001 g
H: 1.0079 g
O: 15.999 g
N: 14.007 g

Sorry, too busy to work it out right now. Well, if I remember correctly you get the number of moles for each element, then you divide all the elements by the lowest amount of moles.

 

[Viper GTS]

Link

Viper GTS

 

[thEnEuRoMancER]

It is kind of a trick question, you should've chosen D - none of the above. If he stated there is a certain mass % of nitrogen in caffeine it should also be in the formula.

BTW: Look at this link. Apparently the molecular formula of caffeine is C8H10N4O2.

 

[iamwiz82]

its B

C8 - 96 g/mol

H10 - 10g/mol

O2 - 32 g/mol

N? = 207 - (96+10+32) = 69 = ~ N5

96/207 ~ 48%

 

[serialb]

Well, simple break down:

49.47% of 207 = 102.4
5.19% of 207 = 10.74
28.8.... Wait


If there are 28.86% of N in caffein, of course it's D!!! :|

Damn it, I should have knew it when I saw caffeine.

serialb

 

[iLoveDivX]

That's the gayest sh*t i have ever seen a teacher do. Why the f*ck would he put a "trick" question on an 8 point question? Especially when none of the other question asked about molecular formula. All of the other ones only asks about empirical. I could have not even touch my calculator and got that question right. Argggggg.

 

[Axman]

B, I believe

EDIT - WRONG - NONE OF THE ABOVE - show me the N

 

[iamwiz82]

let us know the answer when you get the results back, i'm curious to know if i am right.

 

[iLoveDivX]

B? how did you guys get B?

Edit - Edit after your edit.

 

[rpzero]

It's D, none of the above.
Choices ABC didn't contain any Nitrogen so they must be all wrong.