Question

An acid is a component of rancid butter and has a vile stench. Burning 0.44 g of the acid in excess oxygen yield 0.88 g of $C{O}_2$ and 0.36 g of $H_{2}O$ as the only products. Given that the acid contains only C, H, and O and if vapour density of the acid is 44, then which of the following options is not correct about it’s molecular formula?

• A. It contains 4 carbon atoms
• B. It contains 6 hydrogen atoms
• C. It contains 2 oxygen atoms
• D. Its empirical formula contains 2 carbon atoms

Answer 1

The correct option is A It contains 4 carbon atoms

$Molarmass=2\times vapourdensity$
Given, Vapour density = 44, so molar mass = 88 g/mol.
Since the molar mass of the acid is 88 g so,
0.44 g acid $=\frac{0.44}{88}=0.005$ moles of acid.
Similarly, $0.88gC{O}_2=\frac{0.88}{44}=0.02molC{O}_2$ & $0.36g{H}_{2}O=\frac{0.36}{18}=0.02mol{H}_{2}O$
So 0.005 mols acid contains 0.02 mols of carbon and 0.04 mols of hydrogen.
Hence, 1 mol of acid will contain 4 mol of carbon and 8 mol of hydrogen atoms. So, moles of oxygen will be $\frac{88-(12\times 4+1\times 8)}{16}=2$ [since molar mass = 88 g/mol]
So, formula of acid will be $C_4{H}_8{O}_2$.