00:01
To determine the molecular formula, we first need to determine the empirical formula.
00:05
If we assume that we have 100 grams of the sample, then at 68 .2 % carbon, we would have 68 .2 grams carbon, which we can convert into moles carbon using molar mass.
00:19
One mole of carbon is 12 .011 grams carbon.
00:25
At 13 .6 % hydrogen, there would be 13 .6 grams hydrogen, which to convert into moles, we divide by its molar mass of 1 .008.
00:41
And then last of all, we have 18 .2 grams of oxygen, which to get moles, we divide by 16 .00 grams, and we get 5 .68 moles carbon for every 13 .5 moles hydrogen, and 1 .138 moles of oxygen.
01:25
These are not whole numbers, so in an attempt to get whole numbers, we divide each of these by the smaller of the three, and this gives us and we get one mole oxygen for 11 .86 that's closest to 12 and then 4 .99 that's closest to 5 so the empirical formula would be c5h12o that that empirical formula has a molar mass of 12 .011 times 5 plus 1 .008 times 12 plus 16, giving us 88 .151 grams per mole.
02:25
This will also be the molecular formula if the actual molar mass of the compound is the the same as the empirical formula molar mass.
02:35
The actual molar mass can be calculated by taking the mass of the compound and dividing it by its moles...