12. Molecular Mass

What is molecular mass?

The sum of the atomic masses of all atoms in a molecule, expressed in atomic mass units (amu) or Daltons (Da).

What is an atomic mass unit (amu)?

A unit of mass defined as one-twelfth of the mass of a carbon-12 atom.

How do you calculate molecular mass?

• Determine the molecular formula.

• Find atomic masses of each element.

• Multiply atomic masses by the number of atoms.

• Sum the results.

Example: Molecular mass of glucose (C6H12O6)?

Carbon: 6×12.01=72.066 amu
Hydrogen: 12×1.008=12.09612 amu
Oxygen: 6×16.00=96.006 amu
Total = 180.156 amu

What is relative molecular mass?

A dimensionless number expressing the mass of a molecule relative to one-twelfth of the mass of a carbon-12 atom.

Molecular mass vs. Molar mass?

• Molecular Mass: Measured in amu, applies to a single molecule.

• Molar Mass: Measured in g/mol, applies to a mole of molecules.

Why is molecular mass important?

• Helps in stoichiometry for chemical reactions.

• Determines empirical and molecular formulas.

• Crucial for pharmaceuticals and biochemistry.