# Question #878a9

Sep 29, 2016

Manganese(II) chloride tetrahydrate.

#### Explanation:

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

• the anhydrous salt, which in this case is ${\text{MnCl}}_{2}$
• the water of crystallization, which in this case is $4 \text{H"_2"O}$

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

${\text{Mn}}^{2 +} \to$ the manganese(II) cation

The anhydrous salt will be called

${\text{MnCl}}_{2} \to$ 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, $1 \times {\text{MnCl}}_{2}$
• four molecules of water, $4 \times \text{H"_2"O}$

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

$\text{MnCl"_2 * 4"H"_2"O} \to$ manganese(II) chloride tetrahydrate