What is the total mass of oxygen in 1.00 mole of #Al_2(CrO_4)_3#?
Here, I speak of oxygen ATOMS (and not oxygen molecules). Clearly, there are 4 moles of oxygen atoms in one mole of chromate ion. We have a molar quantity of aluminum chromate, and thus there is 12-fold molar quantity of oxygen ATOMS: i.e. a mass of