How many moles of sulfur are contained in a sample of CuSO4 that also contains 3.50 x 1023 oxygen atoms?

Answer 1

first you want to divide by Avogadro's number to convert into moles of O atoms

3.50 x 10^23 / 6.022 x 10^23 atoms/mol = 0.5812 moles of O atoms

from there then you can convert over to moles of CuSO4 by dividing by 4 since there are 4 oxygen atoms for every 1 molecule of the compound

0.5812/4 = 0.1453 moles of CuSO4

then since there is 1 sulfur atom for every 1 molecule that value is the same as the moles of sulfur atoms, meaning that a sample of CuSO4 containing 3.50 x 10^23 oxygen atoms contains approximately 0.145 moles of sulfur

Answer 2

We can use dimensional analysis (unit factor method) to solve this problem. But you must know about Avogadro's number and how to look at a chemical formula and what it means.

1 mole of CuSO4 contains 1 mole of Cu atoms + 1 mole of S atoms + 4 moles of O atoms.

Avogadro's number = 6.02x10²³ atoms / mole

Dimensional analysis:

3.50x10²³ O atoms x 1 mol O / 6.02x10²³ O atoms x 1 mol S / 4 mols O = 0.145 moles of S