What is the total number of atoms in 0.200 mol of ammonium sulfate, (NH4)2SO4? (Avogadro constant = 6.02 × 10^23 mol^-1)
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Correct answer
B. 1.81 × 10^24
Principle or equation
The number of atoms in a sample is obtained by multiplying the number of moles of the substance by the number of atoms per formula unit and then by Avogadro's constant.
Why this answer is correct
Ammonium sulfate has the formula (NH4)2SO4. Count atoms: N:2, H:8, S:1, O:4, total = 15 atoms per formula unit. For 0.200 mol, number of formula units = 0.200 × 6.02×10^23 = 1.204×10^23. Multiply by 15 atoms/formula unit gives 1.806×10^24 ≈ 1.81×10^24 atoms.
Example
For 0.100 mol of Ca(NO3)2, atoms per formula unit = 1+2+6=9, total atoms = 0.100 × 6.02×10^23 × 9 = 5.42×10^23.
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