A colloid is a heterogeneous system in which one substance is dispersed as very fine particles in another substance. Their range of diameters is between 1-1000 nm. Based on dispersed phase and dispersion medium, colloids may be of different types like sol, gel, emulsion, aerosol, foam etc. Based on nature of interaction between two phases, sols are divided into Lyophillic and Lyophobic sols. Colloidal solutions exhibit various properties like Tyndall effect, Brownian movement and Electrophoresis. Stability of colloids is due to presence of charge. If somehow charge is removed, the particles will coagulate. Coagulation rate by various solutions containing ions, is decided by Hardy-Schulze rule. Everyday we come across many colloids. The meals we eat, clothes we wear, wooden furniture etc. are largely composed of colloids.

The range of diameters for colloidal particle is :

\(10^{-9}\) to \(10^{-6}\)m

The correct answer is option 1. \(10^{-9}\) to \(10^{-6}\)m.

Colloidal particles are intermediate in size between those found in true solutions and those in suspensions. They are dispersed throughout a continuous medium (which could be a liquid, solid, or gas). The particles are typically small enough to remain suspended due to Brownian motion but large enough to scatter light.

Characteristics of Colloidal Systems:

Light Scattering (Tyndall Effect): Colloidal particles scatter light, which makes the path of the light visible through the dispersion. This phenomenon is known as the Tyndall effect. True solutions do not exhibit this effect because their particles are too small.

Brownian Motion: Colloidal particles experience random motion due to collisions with molecules of the dispersion medium. This motion helps prevent the particles from settling out of the dispersion, which is a key characteristic of colloids.

Size Range Explanation

True Solutions: Particles in true solutions are less than 1 nanometer (nm) in diameter. This means they are smaller than \(10^{-9}\) meters. True solutions are homogeneous and the solute particles are too small to scatter light. They also do not exhibit the Tyndall effect. Examples include sugar or salt dissolved in water.

Colloidal Range (\(10^{-9}\) to \(10^{-6}\) meters): Colloidal particles range from about 1 nanometer (nm) to 1 micrometer (µm), which is \(10^{-9}\) to \(10^{-6}\) meters. This size range allows them to stay suspended and exhibit light scattering properties. Common colloids include:

Milk: Contains fat globules and proteins in the range of \(10^{-7}\) to \(10^{-8}\) meters.

Fog: Consists of water droplets in the size range of \(10^{-6}\) meters.

Gelatin: Contains particles in the size range of \(10^{-9}\) to \(10^{-8}\) meters.

Suspensions: Particles larger than 1 micrometer (µm) (which is \(10^{-6}\) meters) typically settle out over time due to gravity. Suspensions are heterogeneous mixtures where particles are large enough to be seen and separated by filtration. They do not exhibit the Tyndall effect since the particles are much larger.

Why This Size Range Matters

Stability and Suspension:

Brownian Motion: In the colloidal size range, particles are small enough to remain suspended in the dispersion medium due to Brownian motion. This motion counteracts gravity, preventing the particles from settling out.

Preventing Settling: Particles larger than \(10^{-6}\) meters are more likely to settle out because gravity can overcome Brownian motion.

Light Scattering:

Tyndall Effect: The size of colloidal particles allows them to scatter light effectively. This scattering is not observed in true solutions where particles are too small, nor in suspensions where particles are too large.

Practical Examples and Uses:

The specific size range of colloidal particles makes them useful in various applications such as drug delivery systems, food products, and industrial processes.

In summary, the size range of \(10^{-9}\) to \(10^{-6}\) meters for colloidal particles is critical because it allows these particles to exhibit the characteristic properties of colloids, such as stability in suspension and light scattering. This range differentiates colloids from true solutions and suspensions and is central to the study and application of colloidal systems.