# Stoichiometry and reactions

chemdummy
HELP! I've been having problems with Chemistry the past semester and a half, but stoichiometry is the hardest thing yet. Here's the problem:

Aluminum oxide is formed from the reaction of metallic aluminum with oxygen gas. How many moles of Aluminum are needed to form 3.4 moles of Aluminum oxide?

I've looked around the site and found a thread on it, but it didn't help me completely. So far, I have the balanced equation: 4Al + 3O2 --> 2Al2O3. The ratio is 4/3, but where do I go from there?

dmoravec
Have you ever used factor labeling before? It is also known as dimensional analysis.

http://www.bcpl.net/~kdrews/factorlabel.html [Broken]

using this idea you can convert the units of 3.4 moles of aluminum oxide to aluminum using the ratio 4 moles of aluminum/ 2 moles of aluminum oxide. (In otherwords for each mole of aluminum oxide you wish to create you need 2 of aluminum)

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Mentor

If 4 moles of Al gives 2 moles of oxide, how many moles of Al (x) are needed to produce 3.4 mole of oxide?

4:2 = x:3.4

Solve for x.