A Level Chemistry OCR Practice Exam

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What defines a mole in terms of particles?

The amount of substance containing 6.022 x 10^23 particles
The amount of substance containing 12 g of nitrogen
The amount of substance containing as many particles as there are carbon atoms in exactly 12 g of carbon-12
The amount of substance proportional to the volume

The correct answer is: The amount of substance containing as many particles as there are carbon atoms in exactly 12 g of carbon-12

The correct definition of a mole is fundamentally linked to Avogadro's number, which is 6.022 x 10^23 particles. This number represents the number of atoms, molecules, or other particles in one mole of a substance. Thus, stating that a mole contains 6.022 x 10^23 particles directly aligns with the standard definition of a mole. While the answer that has been selected references the number of carbon atoms in 12 g of carbon-12, it is also an equivalent definition, as it implies that one mole of any substance will always contain 6.022 x 10^23 particles—no matter whether it is carbon or another element. This is foundational to how the mole is defined in terms of counting particles in chemistry. The defining characteristic of a mole, with respect to the number of particles, is unequivocal—1 mole always corresponds to this fixed number of particles when referring to atomic or molecular counts. This clarity and universality in the concept of a mole is essential for stoichiometric calculations in chemistry.