Question #878a9

1 Answer
Sep 29, 2016


Manganese(II) chloride tetrahydrate.


You're dealing with a hydrate, which is a compound that consists of

  • the anhydrous salt, which in this case is #"MnCl"_2#
  • the water of crystallization, which in this case is #4"H"_2"O"#

The first thing to do here is to focus on the anhydrous salt. Notice that the salt contains chloride anions, which as you know carry a #1-# charge.

This implies that the charge on the manganese cation will be equal to #2+#, since you need two chloride anions to balance the total positive charge coming from the cation.

Because manganese is a transition metal, which implies that it can form cations of different charges, you must use a Roman numeral to name it.

In this case, the manganese cation carries a #2+# charge, so add the (II) Roman numeral to its name to get

#"Mn"^(2+) -># the manganese(II) cation

The anhydrous salt will be called

#"MnCl"_2 -># manganese(II) chloride

Now for the water of crystallization. Notice that each formula unit of this hydrate contains

  • one formula unit of manganese(II) chloride, #1 xx "MnCl"_2#
  • four molecules of water, #4 xx "H"_2"O"#

At this point, you must turn to a Greek prefix.

Since you have four water molecules per formula unit of hydrate, use the prefix tetra-.

The full name of the hydrate will thus be

#"MnCl"_2 * 4"H"_2"O" -># manganese(II) chloride tetrahydrate