Question

a hydrocarbon contains 20 percent hydrogen by mass . the emphericall fourmula of the compound is

Answer 1

Since the hydrocarbon contains only carbon and hydrogen only, hence the ratio of the no. of atoms of H:C = 20/1 : 80/12 = 20 : 20/3 = 60 : 20 = 3:1. Hence the empirical formula is CH3.

Answer 2

The empirical formula of the given compound is CH₃.

Given:

The percentage of hydrogen in the hydrocarbon = 20%.

To Find:

We have to find the empirical formula of the hydrocarbon that contains 20 percent of hydrogen by mass.

Solution:

A hydrocarbon is a compound that consists of hydrogen and carbon.

If the compound contains 20% hydrogen by mass, then there will be 80% carbon by mass.

Assume that the mass of the hydrocarbon is 100 g.

∴, The mass of hydrogen = 20% = 20 g.

The number of moles in 20 g hydrogen = $\frac{Mass of hydrogen}{Mass of 1 mole hydrogen} = \frac{20}{1}$ =  20 moles.

The mass of carbon = 80% = 80 g.

The number of moles in 80 g carbon = $\frac{Mass of carbon}{Mass of 1 mole carbon} = \frac{80}{12}$ = 6.67 moles.

The empirical formula is the chemical formula of a compound that gives the proportions of the number of moles of elements present in it.

The ratio is, $C : H = 6.67 : 20 = 1 : 3.$

∴, The empirical formula of given hydrocarbon is CH₃.

Hence, the empirical formula for a hydrocarbon that containing 20% hydrogen by mass is CH₃.

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