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2.8 10-3 mol of CO2 is left after removing 1021 molecules from its ' x ' mg sample. The mass of CO2 taken initially is Given: NA = 6.02 1023 mol-1
(2) 196.2 mg
Concept: moles = NNA = massmolar mass.
Removed = 10216.02 1023 = 1.66 10-3 mol
Initial = 2.8 10-3 + 1.66 10-3 = 4.46 10-3 mol
Mass = 4.46 10-3 44 = 0.196 g ≈ 196.2 mg
Answer: (2)
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