Question

A compound is having molecular weight 56 amu and empirical formula $C{H}_2$, find its molecular formula.

• A. $C_4{H}_8$
• B. $C_6{H}_{12}$
• C. $C_2{H}_2$
• D. $C_2{H}_4$
• E. $C_4{H}_{10}$

Answer 1

Answer: (A)

$C_4{H}_8$

The atomic masses of C and H are 12 amu and 1 amu, respectively.
From the empirical formula $C{H}_2$, the ratio of mass of C to mass of H is $12:2$ or $6:1$
56 g of compound will contain $\frac{56\times 8}{7}=48g$ C and $56-48=8g$ hydrogen.

Number of moles of C $=\frac{48}{12}=4$ moles. Number of moles of hydrogen $=\frac{8}{1}=8$
Hence, the molecular formula is $C_4{H}_8$