Answer: 2e-21 (or 2 × 10⁻²¹)
Explanation:
Since we are starting from the number of atoms of Sulfur, we need to know two sets of formulas:
mass = moles × molar mass
moles = atoms ÷ Avogadro's Number
⇒ mass = (atoms ÷ Avogadro's Number) × molar mass
mass = [(100 atoms) ÷ (6.022 × 10²³ atoms/mole)] × (12.011 g/mol)
= 1.99 × 10⁻²¹ g
≈ 2e-21 [to 1 sig fig]
the mass of a sample of S containing 2.01×10²⁴ atoms is 1.99 × 10⁻²¹ g.
