Calculate the mole of compounds in 15.8g of Fe(ClO4)3?

Answer 1

(15.8 g Fe(ClO4)3) / (354.1968 g Fe(ClO4)3/mol) = 0.0446 mol Fe(ClO4)3

Answer 2

First you need to calculate the molar weight of your compound, Iron(III) Perchlorate.  Divide 15.8 g by the molar weight of your compound and there's your answer.  Molar weight of elements in your compound:

Fe 55.84 g/mol

Cl 35.45 g/mol

O  16 g/mol