How many hydrogen atoms are present in 0.250 mol of ammonium phosphate, (NH4)3PO4? (Avogadro constant = 6.02 × 10^23 mol^-1)
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Correct answer
A. 1.81 × 10^24
Principle or equation
One mole of a substance contains Avogadro's number of entities. The number of atoms of a particular element in a sample 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
The formula (NH4)3PO4 contains 3 nitrogen atoms, 12 hydrogen atoms, 4 oxygen atoms, and 1 phosphorus atom per formula unit. For 0.250 mol of the compound, moles of H atoms = 0.250 × 12 = 3.00 mol. Number of H atoms = 3.00 mol × 6.02 × 10^23 mol^-1 = 1.806 × 10^24, which rounds to 1.81 × 10^24.
Example
For 0.500 mol of water (H2O), moles of H atoms = 0.500 × 2 = 1.00 mol, number of H atoms = 1.00 × 6.02 × 10^23 = 6.02 × 10^23.
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