00:03
Hi there.
00:04
In this question, we are given percent composition.
00:07
We are told that we have 92 .3 percent carbon and 7 .7 percent hydrogen in this compound.
00:18
And we're also given a smaller mass.
00:20
So what we want to find is its molecular formula.
00:23
Well, to do that, what i first want to do is find the empirical formula.
00:29
The empirical formula is the formula that gives the smallest whole number ratio.
00:35
So that's going to be c with a subscript, h with a subscript, and x and y are the smallest whole number ratio that they can be.
00:45
So we need to figure out what x and y are.
00:49
To do that, i need to convert these percents to moles.
00:54
So i'm going to start off doing that by assuming that i have a 100 gram sample.
01:00
Because when you have percent composition, it doesn't really matter what size sample.
01:07
That percent composition is going to be true for any size sample.
01:12
Okay, so if i assume a 100 gram sample, that means 92 .3 percent of 100 is going to be 92 .3 grams.
01:22
And 7 .7 percent of 100 is 7 .7 grams.
01:28
So now that i have grams, i can convert to moles by dividing each by their molar mass.
01:35
So carbon has a molar mass of 12 .01 grams for every.
01:39
Mole and hydrogen's molar mass is 1 .008 grams of hydrogen for every mole.
01:50
This gives me 7 .69 moles of carbon and 7 .64 moles of hydrogen.
02:08
So the two values are nearly the same...