A compound has an empirical formula of CH and a molar mass of 39 g/mol. What is its molecular formula?

• A. CH4
• B. C2H2
• C. C6H6
• D. C3H3

Answer: (D)

Verified step by step guidance

1. Determine the molar mass of the empirical formula CH by adding the atomic masses of carbon and hydrogen: \$12.01\, \text{g/mol} + 1.008\, \text{g/mol}$.
2. Calculate the ratio of the compound's molar mass to the empirical formula mass by dividing the given molar mass (39 g/mol) by the empirical formula mass found in step 1: \(\frac{39}{\text{empirical formula mass}}\).
3. This ratio should be a whole number or very close to it; it represents how many empirical units are in the molecular formula.
4. Multiply the subscripts in the empirical formula CH by this ratio to find the molecular formula. For example, if the ratio is 3, multiply C and H each by 3 to get \(\text{C}_3\text{H}_3\).
5. Verify that the molecular formula's molar mass matches the given molar mass by recalculating the total mass using the new subscripts.