How many hydrogen-bonded water molecule(s) are associated in CuSO4.5H2O ?

In the case of copper(II) sulfate pentahydrate, denoted as CuSO4·5H2O, the "5H2O" indicates that there are five water molecules associated with each formula unit of copper(II) sulfate. This means that for every one CuSO4, there are five water molecules that are hydrogen-bonded to it.

Understanding the Structure of CuSO4·5H2O

To break it down further, let's look at the components:

• CuSO4: This is the anhydrous form of copper(II) sulfate, which consists of one copper ion (Cu²⁺) and one sulfate ion (SO4²⁻).
• 5H2O: This indicates that there are five water molecules, each contributing to the hydration of the copper sulfate.

Hydration and Hydrogen Bonding

When CuSO4 is dissolved in water or crystallizes from an aqueous solution, it forms a hydrate. The water molecules are not just physically present; they interact with the copper and sulfate ions through hydrogen bonding. This interaction stabilizes the structure of the compound and influences its properties.

Each water molecule can form hydrogen bonds with the sulfate ion and the copper ion. The hydrogen atoms in the water molecules are attracted to the negatively charged sulfate ion, while the oxygen atom of the water can interact with the positively charged copper ion. This network of hydrogen bonds is crucial for the stability and solubility of the hydrate.

Implications of Hydration

The presence of these five water molecules significantly affects the physical and chemical properties of CuSO4. For instance:

• Color: Anhydrous CuSO4 is a white powder, while CuSO4·5H2O is a bright blue crystalline solid.
• Solubility: The hydrate is more soluble in water compared to its anhydrous counterpart.
• Thermal Properties: When heated, CuSO4·5H2O loses water and transforms into anhydrous CuSO4, which is an important reaction in various applications.

In summary, the formula CuSO4·5H2O indicates that there are five hydrogen-bonded water molecules associated with each copper(II) sulfate unit. This hydration plays a vital role in the compound's characteristics and behavior in different environments.