# Empirical formula question

i know im not supposed to ask for an answer to a problem, but could someone tell how to go about this question, it should be simple i think..

The molecular mass of a compound of carbon and hydrogen is 42. What is the empirical formula of the compound?

i dont really know what i should do, and guidence would be very appreciated!

thanks,
Alex

## Answers and Replies

This may not be correct - I'm just giving you my best guess.

Since it gives you a compound, there will be whole numbers of C and H. By looking at it, you can figure out that there would be 3 C (3 * 12.01 = 36.03) and 6 H (1.008 * 6 = 6.048). 36.03 + 6.048 ~ 42.

Therefore, the molecular formula is C3H6, which would mean the empirical formula would be CH2.

If you follow the same idea, it could also be C2H18, which would give CH9, but C2H18 isn't a possible compound.

There's probably a better and more correct way of figuring this out, but I think that CH2 should be correct. I'm only in high school, so I'll let someone more experienced in chemistry help you out.

Last edited:
mrjeffy321
Science Advisor
With the information given, that sounds good.
A lot of the time, you might be given an extra bit of information, like the % composition or the products formed after conbustion, to help eliminate some of the trial and error guess work.

CH2 is one of the answers so that is right i believe and your explanation makes sence. i dont like how you have to assume though with the given information, but thank you so much for the help!