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.

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• 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

Would you like to reference this text in a school or academic work? Look:

DAYS, Diogo Lopes. "Nomenclature of hydrated salts"; Brazil School. Available in: https://brasilescola.uol.com.br/quimica/nomenclatura-sais-hidratados.htm. Accessed on June 28, 2021.

Nomenclature of Salts

Salt nomenclature, salt classification, anion name, cation name, iron sulfate, ferrous sulfate, nitrate of silver, potassium chloride, sodium chloride, calcium chloride, silver nitrate, copper sulfate, carbonate calcium.