A student analysed a hydrocarbon X and found it to be containing 43g carbon and 7.2g hydrogen.The relative molecular mass of X was found to be 42.What is the molecular formula of X?
1
-
$\begingroup$ Welcome to chemistry.SE! If you had any questions about the policies of our community, you can visit the help center or take a tour of the website. This is a homework question. We have a policy which states that you should show your thoughts and\or efforts into solving the problem. It'll make us certain that we aren't doing your homework for you. Otherwise, this question may get closed. $\endgroup$– M.A.R.Commented Mar 8, 2015 at 13:44
Add a comment
|
1 Answer
$\begingroup$
$\endgroup$
2
$43\ \mathrm g$ of carbon for $7.2\ \mathrm g$ hydrogen.
Molar mass of carbon is $12\ \mathrm{g/mol}$ and that of hydrogen is $1\ \mathrm{g/mol}$.
Hence there are $\frac{43\ \mathrm g}{12\ \mathrm{g/mol}} = 3.58\ \mathrm{mol} \approx 3.6\ \mathrm{mol}$ of carbon for every $\frac{7.2\ \mathrm g}{1\ \mathrm{g/mol}}=7.2\ \mathrm {mol}$ of hydrogen.
Hence the empirical formula of the compound is $\ce{CH2}$.
Relative molecular mass of $\ce{CH2}$ is $12+2\times1 = 14$. Given relative molecular mass is $42$.
$\displaystyle\frac{42}{14}=3$
Hence the formula of the compound is $\ce{C3H6}$
answered Mar 8, 2015 at 10:40
-
6$\begingroup$ Your answer is correct, well structured and well written (using TeX on your first post, good job!), so you have my upvote. However, for future reference, according to site policy we usually don't directly answer homework questions, especially when the asker shows zero effort in solving them and simply copypastes the problem for us to work on. Just something to keep in mind next time. $\endgroup$ Commented Mar 8, 2015 at 11:34
-
1$\begingroup$ @NicolauSakerNeto I'll keep that in mind! $\endgroup$ Commented Mar 8, 2015 at 11:37