Question

learning: molecules and compounds calculations
question ①
the empirical formula is a chemical formula that provides the smallest, whole-number ratio of elements in a compound.
the molecular formula is a whole number multiple of the empirical formula.
the multiple is determined from the ratio of the molar mass to the empirical formula mass.
whole-number multiple = $\frac{molar mass}{empirical formula mass}$
what is the molecular formula if the molar mass is 30.08g/mol and the empirical formula is ch₃?
answer
$\bigcirc$ c₆h₂
$\bigcirc$ ch₃
$\bigcirc$ c₂h₆
$\bigcirc$ c₂h₄
$\bigcirc$ i dont know yet

Explanation:

Step1: Calculate empirical formula mass

Empirical formula is $\text{CH}_3$. Molar mass of C = 12.01 g/mol, H = 1.008 g/mol.
$\text{Empirical formula mass} = 12.01 + 3\times1.008 = 15.034\ \text{g/mol}$

Step2: Find whole-number multiple

Use given molar mass = 30.08 g/mol.
$\text{Whole-number multiple} = \frac{30.08}{15.034} \approx 2$

Step3: Scale empirical formula

Multiply each subscript in $\text{CH}_3$ by 2.
$\text{Molecular formula} = \text{C}_{2}\text{H}_{6}$

Answer:

C. $\text{C}_2\text{H}_6$