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### HW Problem F15

Posted: Sat Sep 28, 2019 7:22 pm
For reference, this is the textbook question:
Diazepam has the mass percentage composition 67.94% C, 12.49% Cl, 9.84% N, and 5.62% O. What is the empirical formula of the compound?

My question isn't specific to only problem F15 but can be applied to practically the entire section. I understand how to find the ratio of atoms in the empirical formula of the compound, but I don't understand how to determine the order in which to write each element. So, for example, why is the empirical formula of the compound written as C16H13ClN2O? Why isn't the empirical formula written as C16H13N2ClO? Any clarification on this matter would be greatly appreciated.

Also, as a bonus question, does anyone know by what time this week Professor Lavelle expects us to make our five posts on this forum? Do we need to make five posts by tomorrow in order to earn full credit for posting? Or do we need to make five posts by next Friday? I was a bit confused when he was discussing this aspect of his course.

### Re: HW Problem F15

Posted: Sat Sep 28, 2019 9:47 pm
Hi! I just looked it up, and apparently there's this thing called the Hill System Order that explains what order you write each element:
1. Carbon
2. Hydrogen
3. The rest in alphabetical order.
Pretty much, you always put C and H first (in that order) and then the rest alphabetically.
Here's the link I got it from: https://web.cas.org/training/stneasytip ... mula1.html

Also, I'm not completely sure about when the posts are due, but I am gonna assume it's due on Friday with the rest of the homework. Let me know if you find out!

Hope this helps :)

### Re: HW Problem F15

Posted: Sat Sep 28, 2019 10:03 pm
I believe the posts are due by next Sunday. As far as the order goes, after looking it up, the Hill System Order is one way to write it, but you may also write it in a manner where the notation indicates structure. For example, this is why you'll see the (OH) group together rather than being split apart with the H in front.