Hydration facts for kids

When we talk about hydration in chemistry, it means adding water molecules to a chemical substance. Imagine a substance that can exist in two forms: one with water and one without. The form that has water added to it is called a "hydrate." The form without water is called "anhydrous." These two forms can look very different!

For example, tin(IV) chloride without water (anhydrous) is a liquid. But when it has five water molecules attached, it becomes a solid. This solid form is called a pentahydrate.

Another cool example is copper sulfate. Without water, it's white or light green. But add water, and it turns a bright blue! Also, cobalt(II) chloride is blue when it's anhydrous, but it turns red when hydrated. And anhydrous copper(II) chloride is brown, while its dihydrate (with two water molecules) is green.

Counting Water Molecules

When a substance is hydrated, we often use special prefixes to show how many water molecules are attached. These prefixes tell us the exact number of water molecules for each main chemical unit.

Here are some common prefixes and what they mean:

• Mono- means 1 water molecule.
• Di- means 2 water molecules.
• Tri- means 3 water molecules.
• Tetra- means 4 water molecules.
• Penta- means 5 water molecules.
• Hexa- means 6 water molecules.
• Hepta- means 7 water molecules.
• Octo- means 8 water molecules.
• Nona- means 9 water molecules.
• Deca- means 10 water molecules.

So, a "pentahydrate" means there are five water molecules, and a "dihydrate" means there are two.

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  Anhydrous tin(IV) chloride

• 

  Tin(IV) chloride pentahydrate

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  Anhydrous cobalt(II) chloride

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  Cobalt(II) chloride hexahydrate

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  Hydrated and anhydrous copper sulfate

• 

  Anhydrous copper(II) chloride

• 

  Copper(II) chloride dihydrate

See also

In Spanish: Hidratación para niños