Difference Between True Solution and Colloidal Dispersion

Main Difference – True Solution vs Colloidal Dispersion

A solution is a mixture of two or more substances in the liquid phase. A dispersion is a system composed of a mixture of two or more substances that exist as a two-phased system. Some solutions are transparent while other solutions are opaque. A true solution is a clear transparent solution whereas a colloidal dispersion is a turbid translucent mixture. The main difference between true solution and colloidal dispersion is that a true solution is essentially in the liquid phase whereas a colloidal dispersion can exist in different phases.

Key Areas Covered

1. What is a True Solution
      – Definition, Properties, Examples
2. What is a Colloidal Dispersion
      – Definition, Specific Properties, Examples
3. What is the Difference Between True Solution and Colloidal Dispersion
      – Comparison of Key Differences

Key Terms: Colloid, Colloidal Dispersion, Translucent, Transparent, True Solution

What is a True Solution

A true solution is a homogeneous mixture of two or more solutes and a solvent. This mixture is in a liquid phase and is transparent. Therefore, this true solution cannot scatter or reflect light that passes through the solution. The particles in the solution are not visible to naked eye. It has been found that the size of the particles in a true solution is less than 1 nm. These particles are often not visible even under powerful microscopes.

A true solution is essentially a homogeneous mixture. In a true solution, the solute and solvent molecules cannot be distinguished under the microscope. Therefore, the chemical composition and other properties of a true solution are uniform throughout the true solution. A true solution is clear and transparent. The solute and solvent cannot be separated via filtration because both solute and solvent molecules are very small.

Figure 1: Salt Solution is a True Solution

Sugar in water and salt in water are good examples of true solutions. When sugar or salt is dissolved in water, the final solution is a clear transparent solution with other chemical and physical properties similar to a true solution.

What is a Colloidal Dispersion

A colloidal dispersion is a heterogeneous system which is made up of a dispersed phase and a dispersion medium. The dispersed phase is a phase in a two-phased system. It includes colloidal particles. These particles can be finely powdered solid particles, aggregates, droplets, etc. The dispersion medium is the other phase in the two-phased system.  It is the liquid or gaseous medium in which the dispersed phase is distributed.

Figure 2: Silver Halides are Colloidal Dispersions

There are several different types of colloidal dispersions depending on the state of the dispersion medium and the dispersed phase. (Both dispersion medium and dispersed phase can exist in any state of matter: solid, liquid and gas).

Types of Colloidal Dispersions

There are eight main different colloidal dispersions as,

1. Foam
2. Solid foam
3. Liquid aerosol
4. Emulsion
5. Gels
6. Solid aerosols
7. Sol
8. Solid sol

Some common examples of colloidal suspensions include soap, beer, fog, dust, milk, rubber, dust, paste, ink, etc.

Difference Between True Solution and Colloidal Dispersion

Definition

True Solution: A true solution is a homogeneous mixture of two or more solutes and a solvent.

Colloidal Dispersion: A colloidal dispersion is a heterogeneous system made up of a dispersed phase and a dispersion medium.

Nature

True Solution:  A true solution is homogeneous.

Colloidal Dispersion:  A colloidal dispersion is heterogeneous.

Transparency

True Solution:  A true solution is transparent.

Colloidal Dispersion:  A colloidal dispersion is translucent.

Particles Size

True Solution:  A true solution is composed of particles having diameters less than 1 nm.

Colloidal Dispersion:  A colloidal dispersion is composed of particles having diameters 1-100 nm.

Filtration

True Solution:  In a true solution, solute particles cannot be obtained through filtration.

Colloidal Dispersion:  In a colloidal solution, solute particles can be obtained through filtration.

Visibility

True Solution:  The particles in a true solution cannot be observed under the microscope.

Colloidal Dispersion:  The particles in a colloidal solution can be observed from the naked eye or from the microscope.

Conclusion

A solution in chemistry is a liquid mixture containing two or more substances. A dispersion is a heterogeneous mixture of substances that are two different phases. This dispersion of composed of colloids is known as a colloidal dispersion. The main difference between true solution and colloidal dispersion is that a true solution is essentially in the liquid phase whereas a colloidal dispersion can exist in different phases.

References:

1. Helmenstine, Anne Marie. “Learn About Mixture Chemistry, Solutions, Suspensions and More.” ThoughtCo, Available here.
2. “Colloidal Dispersions.” Chemistry Learning, Available here.
3. “Colloidal Solution.” Chemistry Learning, Available here.

Image Courtesy:

1. “SaltInWaterSolutionLiquid” By Chris 73 / Wikimedia Commons (CC BY-SA 3.0) via Commons Wikimeida
2. “Common Silver Halide Precipitates” By Cychr (CC BY 3.0) via Commons Wikimedia