Determine the mass in grams of 2.11 × 10²¹ atoms of arsenic. (The mass of one mole of arsenic is 74.92 g.)

Answer 1

This is a case where you need to make sure you know Avogadro's Number: one mole = 6.022 x 10²³ atoms

To determine our number of moles, we will take our current number of atoms and divide it by Avogadro's Number: 2.11 x 10²¹ / 6.022 x 10²³ = 0.0035 moles.

Now, our last step is to multiply our number of moles by the molar mass to get our grams: 0.0035 moles * 74.92 g/mol = 0.263 g of Arsenic (note 3 sig figs due to 2.11 x 10^21 in question)

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