Nomenclature of hydrated salts

The term hydrated salt applies to a certain type of salts existing. In these salts, we have the presence of a water molecule in their constitution, so much so that the general formula of a hydrated salt is represented as follows:

XY.Z H₂O

• X is any cation;

• Y is any anion;

• Z is the number of water molecules that have joined the single salt molecule XY.

See some examples of hydrated salt formulas:

• AlCl₃.6H₂O

• CUSO₄.5h₂O

• CaCl₂.2H₂O

The naming rule for a hydrated salt is as follows:

Anion name + de + cation name + prefix indicating a + hydrated
quantity of
water molecules

NOTE: The prefixes that are used to indicate the amount of water molecules are: mono (1 H₂O), di (2H₂O), tri (3 H₂O), tetra (4H₂O), penta (5 H₂O), hex (6H₂O) and so on.

Now check out five examples of how to name a hydrated salt:

• AlCl₃.6 H₂O

In this example, the anion is chloride, the cation is aluminum, and there are six molecules of water (hexa). So, its name will be: Aluminum Chloride hexahydrate.

• CUSO₄.5 hours₂O

In this example, the anion is sulfate, the cation is copper II, and there are five molecules of water (hexa). So, your name will be:

Copper II sulfate pentahydrate.

• CaCl₂.2 H₂O

In this example, the anion is chloride, the cation is calcium, and there are two molecules of water (di). So, its name will be: Calcium Chloride Dihydrate.

• At₂ONLY₄.10 hours₂O

In this example, the anion is sulfate, the cation is sodium, and there are ten molecules of water (Deca). So, your name will be: Sodium sulfate decahydrate.

• Case₄.2H₂O

In this example, the anion is sulfate, the cation is calcium, and there are two molecules of water (di). Its name will be: Calcium Sulfate Dihydrate.

We can even assemble the formula for hydrated salt from its name. See some examples:

• Cobalt II chloride tetrahydrate

In this salt, the cation is cobalt, with a charge 2+ (Co²⁺); the anion is the chloride (Cl^1-) and we also have the presence of four water molecules. Therefore, the formula for salt will be:

CoCl₂.4H₂O

NOTE: As the charge of the cation and the anion are different, there must be a crossing between these charges, so the result was CoCl₂.

• Sulfate of magnesium heptahydrate

In this salt, the cation is Magnesium, with a charge 2+ (Mg²⁺, for being from the IIA family); the anion is the sulphate (SO₄^2-) and we also have the presence of seven water molecules. Therefore, the formula for salt will be:

MgSO4₄.7H₂O

By Me. Diogo Lopes Dias

Source: Brazil School - https://brasilescola.uol.com.br/quimica/nomenclatura-sais-hidratados.htm