1.5 g of a gaseous compound of carbon and hydrogen occupies 1.12 dm^3 at STP. What is the mass of 1 mole of this compound and what is its likely formula? Thanks!! will give medal!

Question

preetha · Answer

You have been given volume, and STP.  Soyou can calculate moles of this compound.  1 mole of any gas occupies 22.4 mL at STP.  Calculate the moles and then convert that to molar mass.  Moles = g/molar mass.  Then you will have to look at the molar mass and go some guessing.

anonymous · Answer

i got the No. of moles which is 0.05 mol and the molar mass which is 30 g/mol. Im stuck there. I don't understand what to do to find the formula. please help.

thomaster · Answer

gaseous compound of carbon and hydrogen so $\to \sf\Large C_xH_y$
1 mol gas occupies $\sf 22.4\;dm^3\;(or\;Liter)\$
So $\sf\frac{1.12}{22.4}=0.05\;mol\$ 
$\sf\frac{1.5}{0.05}=30\;g/mol$

$\sf \to(This~it~the~point~where~you~are~now)\gets$
$\Large{\hspace{4pt}\downarrow~\downarrow~\downarrow~\downarrow~\downarrow~\downarrow~\downarrow~\downarrow~\downarrow~\downarrow~\downarrow}\$
Now you have to guess which $\sf C_xH_y$ gas has a molecular weight of 30 g/mol.
Carbon = 12 g/mol (actually it's 12.011 but we can use rough numbers)
Hydrogen = 1 g/mol

First one you'd try is methane
$\sf \large{CH_4}\;\to \normalsize{12+(4*1)}=16 g/mol$

Next possible one is ethane (because the general form is $\sf C_nH_{n+2}$
$\sf \large{C_2H_6}\;\to \normalsize{(2*12)+(6*1)}=30 g/mol$

Now we know that the compound is ethane $\Large\ddot\smile$

$\overline{\underline{\LARGE{\color{gold}{\star~}}\Large\tt\color{green}{I\;Hope\;this\;Helps!}\LARGE{\color{gold}{~\star}}}}$

thomaster · Answer

I made a slight mistake, the general form of a hydrocarbon is not $\large\sf C_nH_{\underline{n}+2}$ its $\large\sf C_nH_{\underline{2n}+2}$

anonymous · Answer

Thanks alot!!!!!!! it helped:)

thomaster · Answer

I'm glad it did $\Large\ddot\smile$