Question

A carbon compound containing only carbon and oxygen has an approximate molecular mass of 290. On analysis, it is found to contain 50% by mass of each element. what is the molecular formula of the compound?

Answer 1

Let the mass of the compound be 100g

Mass of Oxygen = 50g

Moles of Oxygen = $\frac{50}{16}$

Mass of Carbon = 50g

Moles of Carbon = $\frac{50}{12}$

The mole ratio of Carbon to Oxygen= $\frac{50}{12}$:$\frac{50}{16}$= $4:3$

$\mathrm{Empirical}\mathrm{formula}={\mathrm{C}}_4{\mathrm{O}}_3$

$\mathrm{Empirical}\mathrm{mass}=96$

And let the molecular formula is ${\left({\mathrm{C}}_4{\mathrm{O}}_3\right)}_{\mathrm{n}}$

$96\mathrm{n}=290$

$\mathrm{n}=\frac{290}{96}=3$

Therefore, $\mathrm{Molecular}\mathrm{Formula}={\mathrm{C}}_{12}{\mathrm{O}}_9$