alleryStart learning →How is one mole of a substance defined?
AThe mass in grams equal to the formula mass of the substance
BThe amount holding as many entities as atoms in 12 g of carbon-12
CThe number of atoms in one litre of any gas at room conditions
DThe amount of substance that weighs exactly twelve grams
Answer & Solution
Correct answer: B. The amount holding as many entities as atoms in 12 g of carbon-12
1. The mole is an amount unit, in the same family as pair, dozen and gross.
2. It is defined as the amount of substance containing as many discrete entities as there are atoms in exactly 12 g of pure carbon-12.
3. Those entities may be atoms, molecules or ions, so the definition is not restricted to atoms.
4. Only carbon-12 itself weighs 12 g per mole, so a fixed twelve grams cannot define the unit for every substance.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 3 "Composition of Substances and Solutions", section 3.1 Formula Mass and the Mole Concept_
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