Question

If 8.66 X 1021 atoms are removed from 0.055 mole of iron, what mass of iron remains?

Answer 1

According to the definition of the mole, 1 mole of a substance contains a N_A of the formula units: 6.022·10²³. Therefore, 8.66·10²¹ atoms of iron correspond to 8.66·10²¹/N_A =0.0144 mol of iron. The number of the moles of iron left is 0.055 - 0.0144 = 0.0406 mol.

The mass is the product of number of the moles $n$ and molar mass ($M$(Fe) = 55.84 g/mol):

$m = n·M = 0.0406·55.84 = 2.27$ g.

Answer: 2.27 g of iron remains when 8.66 ·10²¹ atoms are removed from 0.055 mole of iron.