Posted by Corey on Wednesday, November 7, 2007 at 8:19pm.
Start with e).
You know N is 43.7%, O is 50.0%, so H must be 100% - those two. Calculate the empirical formula from this. Knowing the density of 2.86 (if it were a gas) calculate the molar mass, then determine the molecular formula.
Now go to f).
g) should give you the molar mass of comound B.
The rest of it then falls into place.
Post your work and we can go from here if you need additonal hints. (How long have you had this marathon problem if it is due tomorrow?)
Well i tried to get the empirical formula but i got H2NO, how do i use the density, 2.86.
H2NO is correct. Now if it were a gas (it isn't) the density would be 2.86. Remember that 1 mol of a gas occupies 22.4 L atr STP. So the molar mass of this material is ??. And that means the molecular formula is ??
I am not sure how to find the molar mass using the 22.4 L at STP
So is H2NO correct?
No. What's the molar mass?
the molar mass is 64.064 g/mol
Now what is the formula mas of the empirical formula you worked out? So now you know the molecular formula is ??
it should be H2NO3
Come on now. You have the molar mass correct at 64. You know the emprical formula is H2NO. So what is the formula mass of the H2NO (that's the emprical formula).All you need to do is add the atomic masses.
Ok so i am done with D
Because when i add the atomic masses i dont' get 64
You are getting ahead of yourself. What is the formula mass of the empirical formula. And what is the molecular formula. (Or tell me what you don't understand).
So what is D.
the formula mass is 32
Good. So if the formula mass is 32 and the molar mass is 64, that means the molecular formula must be ??
NH4NO2
VERY GOOD.
So D is NH4NO2. Now you know what C is? It is ??(from statement f)
C would be NH4NO3
RIGHT
Next I would go to statement g and work out the molar mass of compound B.
Ok but i am confused of how to use the info for B
mols cmpd B = L x M
mols = g/molar mass
Hey i got the molar mass of B to be 330
Surely not. I think you have a decimal point off.
mols = L x M = 0.02198 L x 1.000 M = 0.02198
molar mass = g/mols = 0.726/0.02198= xx
oh ok my bad so the molar mass is 33.03
so now how do i find the formula
ok. Now you know the molar mass is about 33, you know from statement b that compound B has 1 N atom (with a formal charge of zero) AND from statement g that compound B is basic. So you need to put 1 N, an OH, and some H atoms to make 33.
would it be NH2OH
Probably, although you can't be definite about it with just a molar mass, 1 N, basic, and formal charge of zero. Those things fit but to be defnitive you would need an elemental analysis like you went through for compounds C and D.
OK.
Do you know the name of H2NOH?
Now you know B, C, and D. That leaves A and E. Not enough information is available about A or E to be definitive but you can make VERY good guesses about their identity.
would A be HNO3 and E be NH3
That's what I would guess. Statement c is a dead give away. I know HNO3 is sold commercially as 16 M solution and that NH3 is sold commercially as 15 M. Also, I know the bottle is labeled ammonium hydroxide and not aqueous NH3. So these probably are correct. The other statements are consistent with A and E being HNO3 and NH3.
I trust you can do the Lewis dot structures.
yes i can do them so i don't need to do any work for A and E?
Dr. Bob yur a beast:]
i had the same problem for ap chemistry and i looked at what you wrote but could you help me with it
Whoever did this, thank you so much! You just saved my life on this problem and on my next test because it was extra credit and now I actually understand how to do it.
Thanks!
Thanks for working everything step-by-step! Truly appreciate it!