ChemistryA LevelAmount of Substance

Number of particles formula

The number of particles formula as it is used in A Level Chemistry, taken from the A Level Chemistry formula sheet.

The formula

N = n \times N_A

Write the formula down before substituting — most mark schemes award a method mark for a correct, clearly quoted formula.
Check every quantity is in consistent units before you substitute, then substitute in one step so the working stays easy to follow.
Show the rearrangement rather than jumping to the answer, and give the final value to the accuracy the question asks for.

n = \dfrac{m}{M}

n = c \times V

pV = nRT

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