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### M19

Posted: Mon Oct 08, 2018 6:00 pm
how are we supposed to determine the molecular formula of caffeine without looking it up?

### Re: M19

Posted: Mon Oct 08, 2018 6:05 pm
If you're talking about the homework problem it should give you the molar mass of caffeine, and the percent composition. so you would multiply each percentage by the total molar mass. I don't think we should be expected to know the formula for caffeine, considering it's so early in the year.

### Re: M19

Posted: Mon Oct 08, 2018 6:41 pm
The professor said that anything on the test relating to naming compounds are given to you. However once we learn about the composition of the molecules and the names associated with it, then we are expected to know the formula.

### Re: M19

Posted: Mon Oct 08, 2018 8:40 pm
In this problem, you can determine the molecular formula of caffeine by finding the grams of Carbon, Hydrogen, and Nitrogen that are present. Once you add these masses up, you'll see that they do not equal the total mass of the initial hydrogen compound and therefore there has to be another element present in caffeine--oxygen. You would then go about the normal way of finding a molecular formula.

Hope that helps!