Question

The empirical formula of a hydrocarbon is $C{{H}_{3}}$ . Its molecular weight is \[30\], what is molecular formula of the compound
A.\[C{{H}_{4}}\]
 B.\[{{C}_{2}}{{H}_{6}}\]
 C.\[{{C}_{3}}{{H}_{8}}\]
 D.\[{{C}_{4}}{{H}_{10}}\]

Answer 1

Hint: The empirical formula describes in a complex the simplest whole-integer ratio of atoms. In chemistry, the simplest positive integer ratio of atoms contained in a compound is the empirical formula of a chemical compound. Using equation Molecular formula\[=\text{ }n\text{ }\times \] Empirical formula, where \[n\text{ }=\] molecular weight \[/~\] empirical weight , to find molecular formula.

Complete answer:
Molecular weight of $C{{H}_{3}}$ is \[30\] And the weight of the empirical formula $C{{H}_{3}}$ is \[15\]
We know Molecular formula\[=\text{ }n\text{ }\times \]Empirical formula
And \[n\text{ }=\] molecular weight \[/~\] empirical weight.
So, n=30/15
 n=2
Thus Molecular formula\[=\text{ }n\text{ }\times \]Empirical formula
\[=2\times CH3\]
\[={{C}_{2}}{{H}_{6}}\]
So the molecular formula of the compound $C{{H}_{3}}$ is\[={{C}_{2}}{{H}_{6}}\]

Additional Information: Three key types of chemical formulas are available: empirical, molecular and structural. The simplest whole-number ratio of atoms in a compound is shown by empirical formulas; molecular formulas show the number of each type of atom in a molecule, and structural formulas show how the atoms in a molecule bind to each other. $C{{H}_{3}}$is both a chemical formula and an analytical formula. It is also possible to have equal analytical formulas for various types of compounds.
Hence option B: \[{{C}_{2}}{{H}_{6}}\] is the correct answer.

Note: In general, the empirical formula is used to clearly explain what elements in a molecule are present. If one needs to know at a glance what elements they are dealing with, this is useful. When you want to know how many atoms of the elements are present in the compound, the molecular formula is most useful.