Calculating Empirical and Molecular Formulas in Chemistry

Chris Harris from AlloryTutors.com explains how to calculate the empirical formula, which is the simplest whole number ratio of atoms in a compound. The video covers calculating moles from mass and atomic mass, determining the empirical formula, and finding the molecular formula using a multiplier. A worked example is provided, demonstrating the process step-by-step, including handling percentages as mass. The tutorial concludes by linking empirical formula calculations to mass spectrometry, using glucose as an example.

What is an empirical formula?

• The chemical name of a compound

• The total mass of a compound

• The simplest whole number ratio of atoms in a compound

• The exact number of atoms in a molecule

In the example problem, which elements are present in the compound?

• Hydrogen, Oxygen, and Nitrogen

• Carbon, Hydrogen, and Oxygen

• Carbon, Hydrogen, and Nitrogen

• Carbon, Nitrogen, and Oxygen

How do you calculate the number of moles of an element?

• Atomic mass divided by mass

• Mass divided by atomic mass

• Mass multiplied by atomic mass

• Mass plus atomic mass

What is the first step in determining the empirical formula?

• Calculate the molecular mass

• Find the smallest number of moles

• Divide the moles by the smallest number of moles

• Add up the atomic masses

What is the empirical formula of the compound in the example?

• CH2O

• CHO

• C2H4O2

• C6H12O6

How do you find the molecular formula from the empirical formula?

• Add the atomic masses of the empirical formula

• Divide the molecular mass by the empirical formula mass

• Multiply the empirical formula by a multiplier

• Multiply the empirical formula by the atomic mass

What is the molecular formula of the compound if the molecular mass is 180?

• C12H24O12

• CH2O

• C3H6O3

• C6H12O6

What is the multiplier used to find the molecular formula in the example?

• 3

• 6

• 4

• 5

Which scientific tool can help determine the molecular mass of a compound?

• Mass spectrometer

• Barometer

• Spectrophotometer

• Thermometer

What is the significance of knowing the molecular formula?

• It helps in identifying the color of the compound

• It provides the exact number of each type of atom in a molecule

• It determines the boiling point of the compound

• It reveals the taste of the compound