Question

Briefly describe the solution process at the molecular level. Use the dissolution of a solid in a liquid as an example.

Short answer

Dissolution involves breaking solid bonds and forming solute-solvent interactions.

Step-by-step solution

Understanding Dissolution

Dissolution is the process in which molecules of a solid separate and disperse into a liquid, forming a solution. It involves the interaction between the molecules of the solid and the molecules of the liquid.

Intermolecular Forces

To dissolve, the solid's molecules are separated and surrounded by the liquid's molecules. The process depends on breaking intermolecular forces within the solid and establishing interactions with the molecules of the liquid.

Breaking Solid-Liquid Bonds

Solid molecules are held together by cohesive forces, such as ionic or molecular bonds. To dissolve, these forces must be overcome by the attraction between the solid molecules and the liquid molecules.

Interaction with the Solvent

The liquid molecules surround the solid molecules, forming a solvation shell. This is when the solvent-solute interactions become stronger than the solute-solute interactions, allowing the solid to disperse in the liquid.

Achieving Equilibrium

As dissolution proceeds, the solution may reach a point where the rate of dissolving is equal to the rate of re-precipitation. This point is known as the solubility equilibrium.

Key concepts

Intermolecular Forces

Intermolecular forces play a pivotal role in the process of dissolution. When a solid is introduced to a liquid, such as salt in water, its strong cohesive forces need to be disrupted. These forces include ionic, hydrogen bonding, or van der Waals forces, which keep the solid intact.

For dissolution to occur, the attractive forces between the solid's molecules and the liquid's molecules must be greater than the forces holding the solid together. The liquid's molecules exert this attractive pull, first breaking the cohesion between the solid's molecules.

Once overcome, the liquid molecules can surround each solid molecule, leading to dissolution. Understanding these intermolecular forces helps explain why some solids easily dissolve in certain liquids, while others do not.

Solvation Shell

After the intermolecular forces within the solid are broken, each molecule of the solid becomes encased by liquid molecules. This is known as the solvation shell, a critical step in the dissolution process.

The formation of this shell is driven by the attraction between the solute and solvent molecules being stronger than among the solute molecules themselves.

• It involves the orientation of the solvent molecules around the solute to maximize interaction.
• For example, when salt dissolves in water, the water molecules surround and stabilize the individual ions of the salt.

The solvation shell essentially acts as a cushion, allowing the solute molecules to be well integrated into the solvent, fostering a homogenous solution.

Solubility Equilibrium

Once dissolution begins, the process moves toward what is known as solubility equilibrium. This balance point occurs when the rate of the solute dissolving equals the rate of solute particles re-precipitating out of the solution.

At solubility equilibrium, the solution is considered saturated. No more solute can dissolve unless conditions change, such as temperature or pressure.

• It is important in determining how much of a solid can be dissolved in a specific amount of liquid.
• Factors like temperature, pressure, and the nature of the solute and solvent affect this equilibrium. Increasing temperature often increases solubility for solids in liquids.

This concept is crucial for predicting the amounts and concentrations of solutions that can be practically achieved.