Certain hydrocarbon is 92.3 % carbon and 7.7 % hydrogen by mass. If the molar mass of the hydrocarbon is approximately 40 g/mol,

what is its molecular formula?

The hydrocarbon has a molecular formula of C3H3

Explanation:

Step 1: Data given

Suppose the mass of the compound is 100 grams

A hydrocarbon contains:

⇒ 92.3 % carbon = 92.3 grams

⇒ 7.7 % hydrogen = 7.7 grams

Molar mass of the compound is 40 g/mol

Molar mass of carbon = 12.01 g/mol

Molar mass of hydrogen = 1.01 g/mol

Step 2: Calculate moles

Moles = mass / molar mass

Moles carbon = 92.3 grams / 12.01 g/mol

Moles carbon = 7.69 moles

Moles hydrogen = 7.70 grams / 1.01 g/mol

Moles hydrogen = 7.62

Step 3: Calculate mol ratio

We divide by the smallest amount of moles

Carbon: 7.69/7.62 = 1

Hydrogen: 7.62/7.62 = 1

The empirical formula is CH

The molar mass is 13.02 g/mol

Step 4: Calculate the molecular formula

n = 40 g/mol / 13.02 g/mol

n ≈ 3

We need to multiply the empirical formula by 3 to get the molecular formula

Molecular formula = 3 * (CH) = C3H3

The hydrocarbon is C3H3