Molecular mass (also called molecular weight) is the sum of the atomic masses of all the atoms present in one molecule of a substance. It is expressed in atomic mass units (amu or u).
Definition: Sum of atomic masses of all atoms in a molecule.
Unit: amu (u).
H₂O = 18 amu; CO₂ = 44 amu; Glucose = 180 amu.
Molar Mass = Molecular Mass (same number, different units).
To calculate molecular mass, identify all atoms in the molecule and add their atomic masses:
Example 1: Water (H₂O)
Example 2: Carbon Dioxide (CO₂)
Example 3: Glucose (C₆H₁₂O₆)
| Term | Definition | Unit |
|---|---|---|
| Molecular Mass | Mass of one molecule | amu or u |
| Molar Mass | Mass of 1 mole (6.022×10²³ molecules) | g/mol |
Numerically they are the same! Molecular mass of H₂O = 18 u; Molar mass of H₂O = 18 g/mol.
Molecular mass is the sum of atomic masses of all atoms in one molecule of a substance, expressed in atomic mass units (amu).
Molecular mass of water (H₂O) = 2(1) + 16 = 18 amu.
Molecular mass of CO₂ = 12 + 2(16) = 44 amu.
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