How many oxygen atoms are present in 0.300 mol of aluminum sulfate, Al2(SO4)3? (Avogadro constant = 6.02 × 10^23 mol^-1)
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Correct answer
A. 2.17 × 10^24
Principle or equation
The number of atoms of an element in a compound is calculated by multiplying the number of moles of the compound by the number of atoms of that element per formula unit, then by Avogadro's constant.
Why this answer is correct
Each formula unit of Al2(SO4)3 contains 12 oxygen atoms (3 sulfate groups × 4 O each). Moles of O atoms = 0.300 mol × 12 = 3.60 mol. Number of O atoms = 3.60 mol × 6.02 × 10^23 mol^-1 = 2.17 × 10^24.
Example
In 0.100 mol of Ca(NO3)2, there are 6 O atoms per formula unit, so moles of O = 0.600 mol, atoms = 3.61 × 10^23.
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