A hydrocarbon is composed of 85.57% carbon and 14.43% hydrogen and a molar mass of 28.06 mol. What is the molecular formula?

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A hydrocarbon is composed of 85.57% carbon and 14.43% hydrogen and a molar mass of 28.06 mol. What is the molecular formula?

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Answer 1 · 2016-12-16T17:48:50

The stuff is $ethylene$ $"ethylene"$ , $H_{2} C = C H_{2}$ $H_2C=CH_2$ .

Explanation:

As with all these problems, we assume an $100 \cdot g$ $100*g$ mass of compound.

And thus...........

$Moles of carbon = \frac{85.57 \cdot g}{12.011 \cdot g \cdot m o l^{- 1}} = 7.12 \cdot m o l$ $"Moles of carbon"=(85.57*g)/(12.011*g*mol^-1)=7.12*mol$

$Moles of hydrogen = \frac{14.43 \cdot g}{1.00794 \cdot g \cdot m o l^{- 1}} = 14.32 \cdot m o l$ $"Moles of hydrogen"=(14.43*g)/(1.00794*g*mol^-1)=14.32*mol$

We divide thru by the smallest molar quantity (that of carbon) to get an $empirical formula$ $"empirical formula"$ of $C H_{2}$ $CH_2$ .

Now it is a fact that the molecular formula is a whole number multiple of the empirical formula:

i.e. $28.06 \cdot g \cdot m o l^{- 1} = n \times (12.011 + 2 \times 1.00794) \cdot g \cdot m o l^{- 1}$ $28.06*g*mol^-1=nxx(12.011+2xx1.00794)*g*mol^-1$ .

Clearly, $n = 2$ $n=2$ , and the $molecular formula$ $"molecular formula"$ is $C_{2} H_{4}$ $C_2H_4$ .

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A hydrocarbon is composed of 85.57% carbon and 14.43% hydrogen and a molar mass of 28.06 mol. What is the molecular formula?

1 Answer

Explanation:

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