[m453438]

I need to help to resolve this problem. I'm confused. I've trying several ways to resolve it but I can't get the right answer.

Ammonium nitrate will detonate if ignited in the presence of certain impurities. The equation for the reaction at over 300 oC is

2NH4NO3(s) → 2N2(g) + O2(g) + 4H2O(g)

How many grams of ammonium nitrate are required to give 3.3183 g of oxygen gas?

[m453438]

I tried to calculate the limiting reactant but since is one product I don't know how to get the grams of ammonium nitrate

[Borek]

Show how you tried.

[m453438]

First I have the molecular weight of O2 which is 31.9988g, then I converted to moles. Then I multiplied times two moles of ammonium nitrate. Finally I converted the moles of ammonium nitrate to grams. 

[Padfoot]

Don't you have the answer then?

[m453438]

OK here's what i did
3.13183gO2(1 molO2/31.9988 gO2)(2mol NH4NO3/1 mol O2)(80.16344g NH4NO3/1 mol NH4NO3)= 15.69g NH4NO3.

When I put the answer and check it, the computer says "incorrect answer". I don't know if I'm missing something or if I did it wrong.

[Padfoot]

Your working is fine, you just have your molar mass for ammonium nitrate wrong.
http://en.wikipedia.org/wiki/Ammonium_nitrate
Using this value you get 15.67g.

[m453438]

OK thank you.

[m453438]

Computer says again "incorrect answer". 

[Borek]

How many significant digits given? How many you should put in the answer?

[m453438]

Given- 3.13183--> 6 significant figures
Should put in the answer: 6 significant figures
But I'm using these values:
N=14.06674 (7 sig. figs.)
H=1.00794 (6 sig. figs.)
O=15.9994 (6 sig. figs.)
I'm using these values because I need to use a specific periodic table.
Therefore if I calculate the molar weight of ammonium nitrate using these values, this is what I get:  80.16344g. (6 sig. figs.)

Then my result is this:
(3.13183)(2)(80.16344)   =  15.6917008g.     with siginificant figures 15.6917g.
(31.9988)

[m453438]

My answer stills wrong, I don't know why. I think I have the correct number of significant figures. Thank you all for your help but I'm going to sleep and tomorrow I'll ask for help in school.