Difference Between Hydrated Salt and Anhydrous Salt

The key difference between hydrated salt and anhydrous salt is that the hydrated salt molecules are attached to water molecules whereas the anhydrous salt molecules are not attached to any water molecules. If we heat hydrated salts, they emit water molecules as water vapor.

Salts are compounds containing anions and cations in a crystalline form. A salt forms from the combination of the anion of an acid and the cation of a base. There are two forms of salts as hydrated salts and anhydrous salts. These compounds are different from each other according to the presence or absence of water molecules. We call these water molecules “water of crystallization”.

CONTENTS

1. Overview and Key Difference
2. What is Hydrated Salt
3. What is Anhydrous Salt
4. Side by Side Comparison – Hydrated Salt vs Anhydrous Salt in Tabular Form
5. Summary

What is Hydrated Salt?

Hydrated salts are salt compounds that have water molecules attached to the salt molecules. A particular salt compound contains a certain number of water molecules. We call these molecules “water of crystallization” because these salt compounds have water molecules incorporated into the crystallization structure of the salt. These water molecules chemically bind with the salt molecules. These water molecules cause the shape of the crystals.

These hydrated salts form when ionic solids crystallize from aqueous solutions. When we remove this water from the salt crystals, it becomes anhydrous. A common example of a hydrates salt is copper sulfate pentahydrate (CuSO₄.5H₂O). Therefore, if we heat this compound, it converts into anhydrous copper sulfate. That is because when heated, the water molecules evaporate.

What is Anhydrous Salt?

Anhydrous salts are compounds that have no water molecules attached to the salt molecules. We use this term mostly when water of crystallization removes from hydrated salts. Therefore, the term anhydrous refers to a dry salt.

For example, anhydrous sodium sulfate is free of water. Therefore, we can use it as a drying material because it can absorb water and converts into the hydrated form.

What is the Difference Between Hydrated Salt and Anhydrous Salt?

Hydrated salts are salt compounds that have water molecules attached to the salt molecules. These compounds contain water of crystallization. If we heat these compounds, they emit water molecules as water vapor. Anhydrous salts are compounds that have no water molecules attached to the salt molecules. These compounds have no water molecules in the salt crystals.

Summary – Hydrated Salt vs Anhydrous Salt

Salt are derivatives of a combination of acids and bases. There are two forms of salts as hydrated salts and anhydrous salts. The difference between hydrated salt and anhydrous salt is that hydrated salt molecules are attached to water molecules whereas anhydrous salt molecules are not attached to any water molecules.

Reference:

1. “Hydrated Salts.” Transportation of Minerals in Plants. Available here
2. Helmenstine, Anne Marie, Ph.D. “Anhydrous Definition.” ThoughtCo, Jun. 13, 2018. Available here  

Image Courtesy:

1.’Síran měďnatý’By Ondřej Mangl – Own work, (Public Domain) via Commons Wikimedia  
2.’Hydrating-copper(II)-sulfate’By Benjah-bmm27 – Own work, (Public Domain) via Commons Wikimedia