Difference Between Colloid and Solution

Main Difference – Colloid vs Solution

The main difference between colloid and solution is the size of their particles. Particles in solutions are tinier than that of colloids. Solute particles are not visible under a light microscope; however, colloid particles can be seen under the same. 

This article explains, 

1. What is a Colloid?
     – Definition, Properties, Examples

2. What is a Solution?
     – Definition, Properties, Examples

3. How to Separate Colloids from a Solution?
     – Centrifugation, Ultra-filtration, Dialysis

4. What is the difference between Colloid and Solution?

What is a Colloid

A colloid is a state of a particular substance which has a particle size ranging from 1-200 nm. These are not large enough to be a suspension and will not separate out from a solution. A colloidal system consists of colloidal particles which are dispersed in the dispersion medium.  Colloidal solutions often appear opaque due to light being scattered by larger particles. This phenomenon is known as Tyndall Effect.

Examples of Different Types of Colloidal Systems

In the above systems, the dispersed phase always contains particles with sizes ranging from 1-200 nm; hence, these particles are colloids. The dispersion medium is where these particles are dispersed.

What is a Solution

A solution is a combination of a solvent and solute particles. Solute particles are dissolved in the solvent and are of the size < 1 nm. These solute particles are not visible to the naked eye and cannot be filtered through a filter paper. They can be ions, single molecules or crystalloids and are evenly distributed in the solvent. Sugar solutions and salt solutions can be given as examples. A solution is always homogenous and does not settle out on standing. Light passes through solutions without any scattering.

Solvents are mainly liquids. Water is an example of a solvent. There are many organic solvents as well. Dissolution of solute particles depends on polarity. Polar solute particles only dissolve in polar solvents whereas nonpolar solutes dissolve in nonpolar solvents. Some examples are given below.

Water (Polar Solvent) + Salt (Polar Solutes)

Liquid Bromine (NonPolar Solvent) + Solid Iodine (NonPolar Solvent)

How to Separate Colloids from a Solution

Colloids cannot be separated from solution easily. Therefore, methods like centrifugation, Ultra-filtration and Dialysis have to be employed to separate them.

Centrifugation

A solution containing colloids and other impurities can be subjected to a centrifugal force which results in sedimentation of the colloids. Less dense and smaller particles tend to remain in the solution after centrifugation. The solution then can be removed and colloid particles can be recovered.

Ultra-filtration

This method is based on the fact that colloids are unable to pass through certain membranes due to their size. Specially prepared filters with pore size below 1 nm can be employed in this method. Ultra-filters retain the colloid particles and let the smaller particles in the solution pass through. These are prepared by treating normal filter papers with gelatin or collodion which narrow the pore sizes. 

Dialysis

Dialysis is the process of separating colloids from solute particles which are of smaller dimension. This process was discovered by chemist Thomas Graham in 1861. Dialysis process occurs due to the permeability differences of colloids and solute particles (ions, molecules or crystalloids) through a semi-permeable membrane. This method is often used in medical treatments such as treating kidney diseases.

Difference Between Colloid and Solution

Particle Size

The particle size of Colloid is 1-200 nm.

The particle size of Solution is < 1 nm.

Nature

Colloids are heterogeneous.

Solutions are homogeneous.

Permeability

Colloids are only permeable through ultra-filtration papers.

Solutions are permeable through most of the membranes.

Tyndall Effects

Light is scattered by larger particles in Colloids.

Light passes through Solutions.

Appearance of the System

Colloids are translucent. 

Solutions are transparent. 

Neither the solute molecules nor the colloids are chemically bonded to their solvent; therefore, they can be physically recovered.

Reference List:

“Colloidal Solution, True Solution and Suspension | Chemistry Learning.” Colloidal Solution, True Solution and Suspension | Chemistry Learning. N.p., n.d. Web. 26 Jan. 2017.

G, Ellis Sidney, Stevenson Peter C, and Rca Corp. “Patent US2648636 – Method and apparatus for separation of colloids in a colloid solution.” Google Books. N.p., n.d. Web. 26 Jan. 2017.

Volland, Walt. ” Solutions and mixtures .” Online Introductory Chemistry. http://www.800mainstreet.com/, 29 Mar. 2005. Web. 26 Jan. 2017.