Question

Describe briefly what happens when an ionic substance is dissolved in water.

Short answer

When an ionic substance dissolves in water, the polar water molecules interact with the positively charged cations and negatively charged anions, weakening the electrostatic forces holding the substance together. The substance dissociates into individual ions, which then become solvated by water molecules forming a hydration shell around each ion. The ions are stabilized and uniformly distributed, resulting in a homogeneous solution.

Step-by-step solution

Understand the components involved

An ionic substance is composed of positively charged ions (cations) and negatively charged ions (anions) that are held together by the electrostatic force of attraction. When an ionic substance dissolves in water, it means that the substance is broken apart into individual ions, which then become uniformly distributed within the solvent (water).

Role of water molecules

Water is a polar molecule, which means it has a positively charged area (due to the hydrogen atoms) and a negatively charged area (due to the oxygen atom). This polarity allows water molecules to interact with the ions in an ionic substance.

Dissociation of the ionic substance

When an ionic substance is added to water, the negatively charged oxygen atoms of the water molecules will be attracted to the positively charged cations of the ionic substance, and the positively charged hydrogen atoms of the water molecules will be attracted to the negatively charged anions. These attractions will weaken the electrostatic forces that hold the ionic substance together.

Stabilization of the ions

As the ionic substance breaks apart, each ion becomes surrounded by water molecules. The water molecules form a "hydration shell" around each ion, effectively isolating them from each other. This process is known as "solvation" or "hydration" of the ions. The hydration of the ions stabilizes them, making it highly unlikely for them to recombination to form the original ionic substance.

Formation of the solution

The result of the dissociation and solvation of the ions is a homogenous solution, in which the individual ions of the ionic substance are uniformly distributed throughout the water. The ionic substance is now considered to be "dissolved" in the water.