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Calcium phosphate, Ca3(PO4)2, has a formula mass of 310.18 amu. What is the mass of 0.500 mol of calcium phosphate?
A31.02 g
B310.2 g
C620.4 g
D155.1 g
Answer & Solution
Correct answer: D. 155.1 g
1. A formula mass of 310.18 amu means a molar mass of 310.18 g/mol, since the two are numerically equal.
2. Mass equals moles multiplied by molar mass.
3. Substituting gives 0.500 mol x 310.18 g/mol = 155.1 g.
4. Units check: mol x g/mol leaves grams.
5. The value 310.2 g ignores that only half a mole is present, and 620.4 g divides by 0.500 instead of multiplying.
_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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