Solutions and Colloids

 

Introduction

In chemistry and biology, substances often exist in mixtures rather than pure form. These mixtures are generally categorized into solutions, colloids, and suspensions based on particle size and behavior. Understanding these distinctions is essential for students of life sciences, as many biological fluids—like blood and cytoplasm—are colloidal in nature.

A comparison chart showing differences in particle size, appearance, light scattering, and stability between solutions and colloids

What is a Solution?

A solution is a homogeneous mixture of two or more substances. The solute dissolves completely in the solvent, and the particles are not visible to the naked eye or under a microscope.

Characteristics of a Solution:

1. Uniform composition throughout

2. Solute particles are less than 1 nanometer

3. Cannot be separated by filtration

4. Does not scatter light (no Tyndall effect)

Examples of Solutions: Sugar dissolved in water, Salt in water (NaCl solution) and Alcohol in water

What is a Colloid?

A colloid is a heterogeneous mixture where fine particles are dispersed in a continuous medium but do not settle down due to gravity. Colloids are intermediate between true solutions and suspensions.

Characteristics of a Colloid:

1. Particle size between 1 nm to 1000 nm

2. Shows Tyndall effect (scatters light)

3. Cannot be separated by ordinary filtration

4. Appears homogeneous to the naked eye but heterogeneous under a microscope

Examples of Colloids:

Type of Colloid	Dispersed Phase	Dispersion Medium	Example
Sol	Solid	Liquid	Paint, Ink
Gel	Liquid	Solid	Jelly, Cheese
Emulsion	Liquid	Liquid	Milk, Cream
Aerosol	Solid/Liquid	Gas	Fog, Smoke
Foam	Gas	Liquid	Whipped Cream

Differences Between Solutions and Colloids

Feature Solution Colloid Particle Size < 1 nm 1–1000 nm Visibility Not visible Visible under microscope Filtration Cannot be filtered Cannot be filtered Tyndall Effect Absent Present Homogeneity Homogeneous Appears homogeneous Stability Very stable Relatively stable

 Biological Importance of Colloids

1. Blood is a colloidal system containing cells and proteins.

2. Protoplasm in cells behaves like a colloid, aiding in transport and reactions.

3. Colloidal medicines are used for better absorption and controlled release.

Frequently Asked Questions (FAQs)

1. What is the Tyndall effect?

The Tyndall effect is the scattering of light by colloidal particles. Solutions do not show this effect.

2. Is milk a solution or a colloid?

Milk is an emulsion, a type of colloid where fat droplets are dispersed in water.

3. Can colloids be separated by filtration?

No, colloids cannot be separated using ordinary filters but can be separated by ultrafiltration.

4. Is blood a solution or colloid?

Blood is a colloid, consisting of plasma (liquid) and suspended blood cells.

5. What are some common colloids in everyday life?

Examples include milk, butter, gelatin, fog, smoke, and whipped cream.

References

1. Nelson, D. L., & Cox, M. M. (2017). Lehninger Principles of Biochemistry (7th ed.). W.H. Freeman.

2. Stryer, L. (2019). Biochemistry. W.H. Freeman.

3. Atkins, P., & de Paula, J. (2020). Physical Chemistry (11th ed.). Oxford University Press.