Question

A carbon compound containing carbon and oxygen has approximate molar mass equal to $290$. On analysis it is found to contain 50% by mass of each element. Therefore molecular formula of the compound is

• A. $C_{12}{O}_9$
• B. $C_4{O}_3$
• C. $C_3{O}_4$
• D. $C_9{O}_{12}$

Answer 1

The correct option is A $C_{12}{O}_9$

Let the mass of the compound = $100g$
mass of oxygen = $50g$
moles of oxygen= $\frac{50}{16}$
mass of carbon = 50 g
moles of carbon= $\frac{50}{12}$
mole ratio of carbon to oxygen= $\frac{50}{12}:\frac{50}{16}=4:3$

$\therefore$ empirical formula $=C_4{O}_3$
Empirical mass =$96$
And let molecular formula is $(C_4{O}_3{)}_n$
$\therefore 96n=290$
or $n=\frac{290}{96}\approx 3$
$\therefore$ molecular formula is $C_{12}{O}_9$