Question

Calculate the number of moles of Cl atoms in 1.81×10^24 formula units of magnesium chloride,MgCl2.

Answer 1

in 1 mole there are = 6.02*10^23 particles(atoms, molecules, ions, formula units..)
one formula unit of MgCl2 contains 2 Cl atoms(ions in this case)..
so the, 1.81*10^24 MgCl2 should containt 2*(1.81*10^24) atoms...2*1.8*10^24 = 3.6 * 10^24.
if 1 mole contains 6.02*10^23 particles..
then x mole contains 3.6*10^24 particles(in our case it Cl atoms or ions)
by solving this we find approximately 6 moles of Cl(atoms or ions..)