Stoichiometry Part II

So now it is time to turn up the difficulty! You ready?! Well if you're not too bad.

Let's try some examples! The important thing is to create a map and keep organized.

If 121.5 g of Al are consumed, what volume of hydrogen gas is formed at STP?

Plan: mass Al --> moles Al --> moles H2 ---> volume STP

conversion factor for volume is 22.4 L / 1 mol or 1 mol/22.4 L

also, remember your sig figs or you'll get marks off! bad bad bad you dont want that!

121.5 g Al x 1 mol Al  x   3 mol H2    x   22.4 mol H2 = 151 L H2
                    _______      _______         _________
                    27.0 g Al      2 mol Al          1 mol H2

Lets try more!

3Cu(s) + 8HNO3 (aq) + 3Cu(NO3)2 (aq) + 2NO (g) + 4H20 (l)

How many atoms of copper are required to produce 179.2 L of NO gas at STP?

Let's plan!

volume NO --> mol NO --> mol Cu -->  atoms Cu

6.022 x 10 ^ 23 atoms
--------------------
1 mole

is the conversion factor we need to help us solve this problem!

179.2 L NO gas x 1 mol NO x 3 mol Cu x 6.022 x 10^23 atoms Cu
                              ---------     ---------    --------------------------
                              22.4 L       2 moles NO   1 mol Cu

= 7.22 x 10^24 atoms of Cu

There you go! Now you know how to do stoichiometry with atoms, volume at STP and molecules thrown into the mix. You're invincible!

Here are some videos in case you aren't feeling invincible, but I doubt you're not.
Volume to Volume
mass to volume
mass to mass
                             ---------