▁many ▁hyd r ates ▁were ▁unknown , ▁and ▁the ▁dot ▁in ▁the ▁formula ▁of ▁a ▁hyd rate ▁was ▁employed ▁to ▁specify ▁the ▁composition ▁without ▁indicating ▁how ▁the ▁water ▁is ▁bound . ▁ ▁Ex amples : ▁Cu SO 4 ▁- ▁co pper ( II ) ▁sul f ate ▁pent ah yd rate ▁Co Cl 2 ▁- ▁c ob alt ( II ) ▁ch lor ide ▁hex ah yd rate ▁Sn Cl 2 ▁- ▁tin ( II ) ▁( or ▁st ann ous ) ▁ch lor ide ▁di h yd rate ▁For ▁many ▁sal ts , ▁the ▁exact ▁bond ing ▁of ▁the ▁water ▁is ▁un important ▁because ▁the ▁water ▁mole cules ▁are ▁l abil ized ▁upon ▁dissol ution . ▁ ▁For ▁example , ▁an ▁a que ous ▁solution ▁prepared ▁from ▁Cu SO 4 ▁and ▁an h yd r ous ▁Cu SO 4 ▁behave ▁ident ically . ▁ ▁Therefore , ▁knowledge ▁of ▁the ▁degree ▁of ▁hyd r ation ▁is ▁important ▁only ▁for ▁determ ining ▁the ▁equivalent ▁weight : ▁one ▁mole ▁of ▁Cu SO 4 ▁we igh s ▁more ▁than ▁one ▁mole ▁of ▁Cu SO 4 . ▁ ▁In ▁some ▁cases , ▁the ▁degree ▁of ▁hyd r ation ▁can ▁be ▁critical ▁to ▁the ▁resulting ▁chemical ▁properties . ▁ ▁For ▁example , ▁an h yd r ous ▁Rh Cl 3 ▁is ▁not ▁sol ub le ▁in ▁water ▁and ▁is ▁relatively ▁useless ▁in ▁organ omet all ic ▁chem istry ▁whereas ▁Rh Cl 3 ▁is ▁vers atile . ▁ ▁Similarly , ▁hyd r ated ▁Al Cl 3 ▁is ▁a ▁poor