Difference Between Colloid and Crystalloid

Main Difference – Colloid vs Crystalloid

The main difference between colloid and crystalloid is their particle size. Colloidal systems have much larger particles compared to crystalloid systems. Hence, the permeability of colloidal systems is lower than that of crystalloid systems. The base for this difference was first identified by the English scientist, who classified these two systems into two categories depending on their ability to pass through a parchment paper. He declared that the rate of diffusion of crystalloid fluids through a parchment membrane is higher than that of colloidal fluids, the reason being the larger size of the latter. However, it was later discovered that colloid and crystalloid are not particles, but states of a certain substance depending on its particle size.

This article explains,

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

2. What is a Crystalloid System?
     – Definition, Types, Properties, Application, Examples

3. What is the difference between Colloid and Crystalloid?

What is a Colloidal System

A colloidal system is mainly a heterogeneous system. It consists of finely divided particles of one substance, which is dispersed in any other medium. The particle size of these ranges from 1-200 nm. The dispersion medium is where these colloidal particles are dispersed. These entities are generally molecules or molecular aggregates. These particles are associated with phenomena like diffusion, Brownian motion, and osmosis.

Types of Colloidal Systems

Gas and Gas systems always make true solutions.

A colloidal system where a solid is dispersed in a liquid is called a colloidal solution or a sol. These solutions are named according to their dispersion medium.

Colloidal systems are considered to be metastable, which means that the two phases tend to separate on standing for a very long time. Hence, this is a slow process.

There are two types of colloidal systems. They are called lyophilic and lyophobic. In lyophilic systems, dispersed particles have a great affinity to the dispersion medium, and in lyophobic systems, the opposite happens. In such systems, the repulsion forces are greater between the dispersed phase and the dispersion medium.

In addition to the uses mentioned above, colloids of proteins are used to prepare intravenous fluids in medicine.  These remain a long time and increase intravascular volume and are hence called volume expanders.

What is a Crystalloid System

Particles which are less than 1nm in size are classified as crystalloid particles. These make true solutions if dispersed in another medium. However, these can be recovered by evaporating the dispersion medium. For an example, salt (NaCl) can be dissolved in water completely. However, if water is evaporated, salt can be recovered in crystalline form. Thus the crystalloid particles of salt are small enough to get dissolved completely and make a true solution, however, they can be recovered as well.

Sugar solutions and salt solutions are mainly considered as crystalloid systems. These crystalloid particles can easily pass through semi-permeable membranes due to their small size compared to colloid particles.

Saline is one of the most popular salt crystalloid solutions. Lactose and Dextrose are known sugar crystalloid solutions.

Crystalloids are classified according to their tonicity. Tonicity refers to the ability of an extracellular fluid to move water in and out of a cell by osmosis. There are three categories;

Hypertonic– Water will move out of the cell where there is a higher solute concentration.

Hypotonic– The solute concentration is higher inside the cell compared to the outside. Therefore, water moves from outside into the cell.

Isotonic– Both inside and outside of the cells have the same solute concentration, therefore, water does not move.

Because of the properties mentioned above of crystalloids, they are often used in the preparation of intravenous fluids.

Intravenous Fluid

Difference Between Colloid and Crystalloid

Particle Size 

Colloid: Colloid systems have larger particles (1-200 nm).

Crystalloid: Crystalloid particles are comparatively smaller (<1 nm).

Type 

Colloid: Colloidal systems are heterogeneous systems.

Crystalloid: Crystalloid systems are always true solutions.

Permeability

Colloid: Permeability is comparatively low.

Crystalloid: Permeability is comparatively high.

Categories

Colloid: Collodi systems can be categorized as Lyophilic and Lyophobic.

Crystalloid: Crystalloid systems can be categorized as Hypertonic, Hypotonic and Isotonic.

Application

Colloid: Collodi systems are used in paint industry, food industry, perfume industry and various other industrial applications.

Crystalloid: Crystalloid systems are used in medication.

Examples

Colloid: Milk, Shampoo, Gemstones and Foam rubber are examples of Colloid systems.

Crystalloid: Intravenous Fluids (Saline, Sugar solutions) are examples of Crystalloid systems.

Reference:

Comprehensive Practical Chemistry XII Chapter 2, surface chemistry By Dr. N. K. Verma, B. K. Vermani, K . K. Rehani

Sarquis, J.; Colloidal systems.J. Chem. Educ., 1980, 57(8), p 602DOI: 10.1021/ed057p602