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Problem 78 Easy Difficulty

A compound with empirical formula CH was found by experiment to have a molar mass of approximately 78 g. What is the molecular formula of the compound?

Answer

$(\mathrm{CH})_{6}(\text { or }) \mathrm{C}_{6} \mathrm{H}_{6}$

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Video Transcript

Okay. Now we have a compound with the empirical formula of C h. Very simple. So for every mole of carbon, you have equal moves of hydrogen. So this is the impeccable formula, and we want to find the molecular formula inside of me to do, um x y I can just do X ups speakers. They're equal on molar ratios of each other, these two elements. So what we have is the molecular formula Equalling 78 fans per more. Uh, we always need the local formula and the empirical I'm looking or wait to be able to find, you know, like the formula. So, um, first thing we need to do is trying to be mortal formula off the impure. The molecular weight of the empirical formula makes sense. So I'll need to do is look at all the elements we have and to the numbers, the numbers of thumb, which is 11 and just sum it up the their individual Moller eights. So carbon when more urban is 12 basically grams per mole. This is Gramps grams per mole. And then one more of 100 gin. One more slash one Meow. Meow. When adam nations it weighs one, basically one gram per mole. It's the Mueller rate of Introgen. So it's important for us to people of the decimals digits, so you know it will be easier. We'll get, like, more significant digits and more accuracy if when we do the later part. So there's basically equals 13 0.1 864 That is Thean No, the molecular weight of ch compound grams per more. Okay, so let's let me try to make this intuitive to you. So this is the molecular weight for the company world King for And this is the Michael a rate of its, you know, most basic empirical formula. So if these two numbers this number is a multiple of this number, so we just need to, like, find how may need is just a simple division. See how many see ages are in 78 grams from off. So then you just do a simple division 78 divided by this 13.0, one it's it's for That's the 13 decimal. Whenever families promote, it will cancel out, and we basically get 5.9. And if you keep all the digits, gonna right from you can see them over here. Basically, go 5.99 which we can assume to be six. So this is what basically the exes are there? Six. So this compound is just X equals? Yes. X equals the division of the molecular formula for the the molecular weight of the of the month color formula divided by the molecular weight of the empirical formula. That's what the X sub strips equal basically equals C six h tooks much later on You wearing that? This is a good old benzene.

McMaster University
Top Chemistry 101 Educators
Lizabeth T.

Numerade Educator

Morgan S.

University of Kentucky

KS
Karli S.

Numerade Educator

Jake R.

University of Toronto