True Solution vs. Colloidal Solution — What's the Difference?

A True Solution is a homogeneous mixture where the solute is completely dissolved in the solvent at the molecular or ionic level, resulting in a clear and stable solution. Examples include saltwater or sugar dissolved in water. In contrast, a Colloidal Solution (or colloid) is a mixture where the solute particles are larger than those in a true solution but small enough to remain suspended in the solvent, leading to a heterogeneous mixture. Milk and fog are common examples of colloidal solutions.

The particle size in a True Solution is typically less than 1 nanometer, which is small enough to pass through most filters and membranes. This small size also prevents the scattering of light, making true solutions transparent. In Colloidal Solutions, particle sizes range from 1 to 1000 nanometers. These larger particles can scatter light (Tyndall effect) and are usually visible under a microscope.

In True Solutions, the dissolved solute does not settle upon standing and cannot be separated by filtration. The uniform distribution of particles ensures consistency throughout the solution. Colloidal Solutions, however, may exhibit the settling of particles over time and can sometimes be separated into their components by special techniques like centrifugation.

The stability of a True Solution is due to the strong interaction between the solute and solvent at the molecular level. There's no risk of the solute separating out under normal conditions. Colloidal Solutions, while generally stable, can be destabilized by factors like heating or adding certain substances, causing the particles to aggregate and settle out.

In summary, True Solutions and Colloidal Solutions differ primarily in particle size, homogeneity, light scattering properties, and methods of separation. True Solutions are molecularly homogeneous and clear, while colloids have larger particles that are stable but not as uniformly distributed as in true solutions.