In order to etch my own printed circuit board, I bought some ferric chloride.
The seller instruction is to dissolve 40g in 110.5ml of water.
To concoct 1 molar solution of FeCl3, according to its molecular weight, one will need 162.2g for every 1L of water.
So with 100ml, 16.22g is needed.
40/110.5*100/16.22 = 2.232mol.