The relative formula mass is the mass of a formula unit compared to 1/12th the mass of a carbon-12 atom. The relative formula mass of a formula unit is the sum of the relative atomic masses of the elements in the empirical formula.For example, the relative formula mass of sodium hydroxide NaOH is 23.0 + 16.0 + 1.0 which is 40.The relative formula mass is used for substances that do not exist as individual atoms or discrete molecules but exist as giant structures (lattices). It therefore gives the ratios of the atoms of each element.
Relative Formula Mass
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Specification: AQA Chemistry (7404), AS-level, 3.1.2.1 Relative atomic mass and relative molecular mass. Topic: Amount of Substance.
Key terms in this lesson
- Empirical formula
- The simplest whole number ratio of atoms of each element in a compound.
More in Amount of Substance
- Relative Atomic Mass
- Relative Molecular Mass
- The Mole and The Avogadro Constant
- Calculating the Number of Moles
- Example Question - 1
- Example Question - 2
- Mass Concentration
- Example Question - 1
All 33 lessons in Amount of Substance · All AQA AS-level Chemistry topics