00:01
So knowledge of our percent composition can be very valuable to help us identify an unknown compound.
00:10
So first, let's just walk through how you get the percent composition by mass.
00:14
So if we're starting out with h2o, we know that the molar mass is 18 grams per mole, and that the molar mass of the individual h atoms are one gram per mole, and the individual oxygen atom is 16 grams per mole.
00:35
Now, all you do define the percent composition is take the ratio of the molar mass of the individual atom.
00:45
So for hydrogen, there's two of them.
00:47
So we have two grams per mole over the total, over 18 grams from all.
00:51
And we get 11%.
00:53
Now, the same thing for oxygen.
00:55
One oxygen atom is 16 grams from all divided by the total.
00:58
18 grams from all is 88%.
01:01
So now, we can use these percents to help us find an empirical formula.
01:10
And how you do this is we can just assume that, let's just say we assume we have 100 grams of something, of this compound, and we know that our percent compositions.
01:23
So if we multiply our 100 grams times 11 percent, or the decimal, which is 0 .111, we get about 11 grams of hydrogen.
01:43
Okay.
01:45
So now let's convert that into moles.
01:48
So we know that hydrogen has a molar mass of 1 gram per mole...
