IIT/JEE Chemistry Practice #8: Molecular Formulas

The video tutorial covers solving problems related to empirical and molecular formulas. It begins with an introduction to the concepts, followed by a detailed walkthrough of two example questions. The first question involves determining the molecular formula of a compound given the mass ratio of its elements and its molecular mass. The second question involves finding the empirical formula of a hydrocarbon based on the masses of water and carbon dioxide produced during combustion. The tutorial emphasizes converting mass ratios to moles and using these to derive formulas.

What is the molecular formula of a compound with a 9:1:3.5 mass ratio of C, H, and N, and a molecular mass of 108 amu?

• C3H4N

• C12H16N4

• C6H8N2

• C9H12N3

How do you convert mass ratios to moles for determining the empirical formula?

• Multiply the mass by the molar mass

• Multiply the mass by the atomic mass

• Divide the mass by the atomic number

• Divide the mass by the molar mass

What is the empirical formula of a compound with a 3:4:1 mole ratio of C, H, and N?

• C9H12N3

• C12H16N4

• C6H8N2

• C3H4N

In combustion analysis, what does the carbon in CO2 represent?

• Carbon from oxygen

• Carbon from water

• Carbon from the hydrocarbon

• Carbon from the air

What is the molar mass of carbon dioxide?

• 32 g/mol

• 44 g/mol

• 18 g/mol

• 12 g/mol

How do you calculate the mass of carbon in CO2 from combustion?

• Divide the mass of CO2 by 0.273

• Divide the mass of CO2 by 0.111

• Multiply the mass of CO2 by 0.111

• Multiply the mass of CO2 by 0.273

What is the empirical formula of a hydrocarbon if the mole ratio of C to H is 7:8?

• C5H5

• C6H6

• C8H7

• C7H8