Here's what happens:

1. Dissociation: Copper(II) nitrate is an ionic compound. When it dissolves in water, the strong polar water molecules surround the ions and pull them apart, breaking the ionic bonds.

2. Hydration: The separated copper(II) ions (Cu²⁺) and nitrate ions (NO₃⁻) become surrounded by water molecules. This process is called hydration.

3. Solution formation: The hydrated copper(II) ions give the solution its characteristic blue color.

The chemical equation for this process can be written as:

Cu(NO₃)₂(s) → Cu²⁺(aq) + 2NO₃⁻(aq)

This means that solid copper(II) nitrate (Cu(NO₃)₂) dissolves in water to form copper(II) ions (Cu²⁺) and nitrate ions (NO₃⁻) in solution.