IIT/JEE Chemistry Practice #3: Empirical/Molecular Formula

Dave explains how to solve a problem involving empirical and molecular formulas of a hydrocarbon. The problem provides data on carbon and hydrogen mass ratios and conditions of the hydrocarbon vapor. Using the ideal gas law, the number of moles is calculated, followed by determining the molar mass. The empirical formula is derived by converting mass to moles and finding the carbon to hydrogen ratio. The empirical formula matches the molecular formula, concluding the problem with C7H8 as the answer.

What is the mass of carbon per gram of hydrogen in the hydrocarbon?

• 20.5 grams

• 10.5 grams

• 5.0 grams

• 15.0 grams

Which law is used to calculate the number of moles of the hydrocarbon?

• Avogadro's Law

• Ideal Gas Law

• Charles's Law

• Boyle's Law

What is the calculated number of moles of the hydrocarbon?

• 0.0304 moles

• 0.0403 moles

• 0.0604 moles

• 0.0504 moles

What is the molar mass of the hydrocarbon?

• 82.1 grams per mole

• 92.1 grams per mole

• 112.1 grams per mole

• 102.1 grams per mole

What is the empirical formula of the hydrocarbon?

• C6H6

• C7H8

• C8H10

• C9H12