Empirical Formulas and Molecular Formulas Quiz

Study Notes

Empirical Formulas and Molecular Formulas

Glucose has the molecular formula C6H12O6; its empirical formula is CH2O, indicating the simplest whole-number ratio of atoms.

Hydrocarbon Composition

A hydrocarbon with 75% carbon implies the remaining 25% is hydrogen.
Use the ratio of masses to determine the molecular formula: C: 75g, H: 25g.
The molar mass of carbon is 12 g/mol and hydrogen is 1 g/mol.
Calculate moles: 75g C = 6.25 moles; 25g H = 25 moles.
The simplest ratio results in a molecular formula of C3H4.

Sulfur Oxide Composition

An oxide of sulfur with 50% sulfur means 50% is oxygen.
Given that sulfur has a molar mass of approximately 32 g/mol and oxygen approximately 16 g/mol, the masses can help find the empirical formula.
Calculate moles: 50g S = 1.56 moles S; 50g O = 3.12 moles O.
The simplest and whole-number ratio gives the empirical formula as SO2.

Hydrocarbon from Carbon and Hydrogen

A compound with 80% carbon and 20% hydrogen indicates a high carbon ratio.
Calculate moles: 80g C = 6.67 moles; 20g H = 20 moles.
This leads to a molecular formula of C4H10.

Nitrogen Compound

A compound containing 45.2% nitrogen suggests the remainder is likely other elements (e.g., hydrogen or oxygen).
Assuming the rest is hydrogen and a total composition of 100%, calculate: 54.8% hydrogen.
Calculate moles: 45.2g N = 3.22 moles N; 54.8g H = 54.8 moles H.
The simplest ratio leads to an empirical formula of NH2.

Description

Test your knowledge on empirical formulas and molecular formulas with this quiz. Answer questions on compounds with the same empirical formula as glucose and determine the molecular formula of a hydrocarbon based on its carbon content. Challenge yourself and see how well you understand these concepts.