An hydrocarbon is $92.3%$ with respect to carbon. What is its empirical formula? And if the mass of the molecule is $26gmol^-1$ , what is its molecular formula?

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Answer 1 · 2016-04-28T14:56:44

It is likely acetylene.

We assume 100 g of compound, and divide thru by the atomic masses:

$(92.3*g)/(12.011*g*mol^-1)$ $=$ $7.65*mol*C$

$(7.69.3*g)/(1.00794*g*mol^-1)$ $=$ $7.65*mol*H$

So, clearly, the empirical formula is $CH$ .

But we have been given a molecular mass, and it is a fact that the molecular formula is always a multiple of the empirical formula:

$"Molecular formula"$ $=$ $nxx("empirical formula")$

$26*g*mol^-1$ $=$ $nxx(12.011+1,00794)*g*mol^-1$

Clearly, $n$ $=$ $2$ , and molecular formula $=$ $C_2H_2$ , likely acetylene, $HC-=CH$ .

An hydrocarbon is 92.3%92.3% with respect to carbon. What is its empirical formula? And if the mass of the molecule is 26*g*mol^-126*g*mol^-1, what is its molecular formula?