Question

Arrange the following according to the instructions given in brackets :
Ethane, methane, ethene, ethyne. (In the increasing order of the molecular weight) $(\mathrm{H}=1,\mathrm{C}=12)$.

Answer 1

Definition of the molecular formula:

The total of the atomic weight values of the atoms in a molecule is called molecular weight.

Methane$\left({\mathrm{CH}}_4\right)$ has $1$ Carbon$\left(\mathrm{C}\right)$ atom and $4$ Hydrogen$\left(\mathrm{H}\right)$ atoms in it

$\therefore (1\times 12)+(4\times 1)=16g$

Ethane$\left({\mathrm{C}}_2{\mathrm{H}}_6\right)$ has $2$ Carbon$\left(\mathrm{C}\right)$ atom and $6$ Hydrogen$\left(\mathrm{H}\right)$ atoms in it

$\therefore (2\times 12)+(6\times 1)=30g$

Ethene$({\mathrm{CH}}_2={\mathrm{CH}}_2)$ has $2$ Carbon$\left(\mathrm{C}\right)$ atom and $4$ Hydrogen$\left(\mathrm{H}\right)$ atoms in it

$\therefore (2\times 12)+(4\times 1)=28g$

Ethyne$(\mathrm{CH}\equiv \mathrm{CH})$ has $2$ Carbon$\left(\mathrm{C}\right)$ atom and $2$ Hydrogen$\left(\mathrm{H}\right)$ atoms in it

$\therefore (2\times 12)+(2\times 1)=26g$

Therefore, the increasing order of the molecular weight of the given compounds is as follows.

$Methane<Ethyne<Ethene<Ethane$