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
- the water of crystallization, which in this case is
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
This implies that the charge on the manganese cation will be equal to
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
#"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