Homework Help: Chemistry

Posted by Summer on Tuesday, June 14, 2011 at 1:14pm.

Each molecule of NO2, nitrogen dioxide, consists of 1 atom of N and 2 atoms of O. If you have 0.155 g. of NO2, how many molecules of NO2 do you have ?
If you could, please include steps as to how to do the problem.
Thank you

Chemistry - DrBob222, Tuesday, June 14, 2011 at 2:45pm
How many moles NO2 do you have? That is grams/molar mass = 0.155/46.0 = about 0.003 (but you need to do it more accurately).
1 mole NO2 contains how many molecules NO2. 1 mole of NO2 contains 6.022E23 molecules; so how many molecules NO2 do you have? That is 0.003 moles NO2 x (6.022EE23 molecules/mole) = about 2E21.
Chemistry - Summer, Tuesday, June 14, 2011 at 3:12pm
Thank you :)
2030000000000000000000 was the correct answer
Part 2:
How many atoms of N do you have ?
Chemistry - DrBob222, Tuesday, June 14, 2011 at 4:14pm
Many profs will count your answer as incorrect. By placing that many zeros after the number you indicate there are 21 significant figures and that isn't correct. There are only 3 (dictated by the 0.155 gram in the initial sample) so the correct way to show this is 2.03E21.
For the correct number of N atoms, there is 1 N per NO2 molecule; therefore, the number of atoms N is the same as the number of molecules of NO2. There will be twice that number for the number of O atoms.
Chemistry - Summer, Tuesday, June 14, 2011 at 4:30pm
Our work is online, and I tried to enter it as 2.03E21 and it would not accept it.
It only accepts the answer if everything is correct.
Thank you :)
Chemistry - DrBob222, Tuesday, June 14, 2011 at 6:45pm
OK. I suppose you play the game the way it works; however, 2.03E21 is the correct way of writing that number.
Chemistry - Summer, Tuesday, June 14, 2011 at 7:37pm
Than you can be the one to tell my prof that, sir :)

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