Question

If the simplest formula of a substance X is $C{H}_2$ and its molecular mass is $56$, what is its true formula of X?

• A. $C{H}_2$
• B. $C_2{H}_4$
• C. $C_3{H}_4$
• D. $C_4{H}_8$
• E. $C_5{H}_{10}$

Answer 1

Answer: (D)

$C_4{H}_8$

The empirical formula is $C{H}_2$.
The atomic masses of C and H are 12 g/mol and 1 g/mol respectively.
The empirical formula mass is $12+2\left(1\right)=14$.
The molecular mass is 56.
$n=\frac{56}{14}=4$
The molecular formula is $(C{H}_2{)}_n=(C{H}_2{)}_4=C_4{H}_8$.