Characteristics of solid state

• They have definite shape due to strong Intermolecular forces of attraction.
• They have distinct boundaries.
• They have a fixed volume.
• They cannot flow.
• They have negligible compressibility due to negligible distance between the neighbouring molecules.
• They possess a tendency to uphold their shape when exposed to external force.
• They break under force but it is difficult to change their shape so they are rigid.

Solids are rigid, because of the relative stronger intermolecular attractions between them as compared to solids and liquids. Those all forces are electrostatic in nature. By supplying heat the increased kinetic energy of the molecules by which we can change the shape or volume of the substance.

Protection of Colloids

Lyophobic sols such as those of metals like gold, silver etc. can be easily precipitated by the addition of a small amount of electrolytes.

They can be prevented from coagulation by the previous addition of some stable lyophilic colloids like gelatin, albumin, etc. This is because when a lyophilic sol is added to the lyophobic sol, the lyophilic particles form a layer around the lyophobic particles and this protect them from electrolytes.

If a small amount of gelatin is added to gold sol, it is not readily precipitated by the addition of sodium chloride. This process of protecting the lyophobic colloidal solutions from precipitation by the electrolytes due to the previous addition of some lyophilic colloid is called protection. The colloid which is added to prevent coagulation of the colloidal sol is called protecting colloid.

Dehydration reaction is a type of chemical reaction wherein water is formed from the extraction of the components of water from a single reactant. An alkene is produced when dehydration of an alcohol is performed. A basic structural equation for alcohol dehydration is as follows:

C₂H5₅OH → C₂H₄ + H₂O.

Basically, it is a measure of how much the solvent molecules tend to escape from a liquid or solid phase into the atmosphere. Vapor pressure of a liquid is a colligative property.

Electrophoresis and electro-osmosis

• In electrophoresis, solid particles (macromolecule like nucleic acids or protein) is moved using an electric field. But in electro-osmosis, a liquid is moving.
• In electrophoresis, the support solid material is a gel. But in electro-osmosis, it can be a gel, membrane, capillary, etc.

Tyndall effect:- Tyndall effect is a scattering of light when a light beam is passed through a colloidal.

Example;- Shining a flashlight beam into a glass of milk is an excellent demonstration of Tyndall effect.

Colligative properties are properties of a solution which depend only on the number of particles like ions or molecules of the solute in a definite amount of the solvent but not on the nature of the solute.

Lyophilic & Lyophobic Colloids:

Lyophilic colloids can be prepared by just heating the solid with the liquid dispersion medium.

Whereas the lyophobic colloids cannot be prepared just by heating, they need to be prepared by some special methods.

The two methods by which the lyophobic colloids can be prepared are as follows:

1. Dispersion method

2. Aggregation method

Preparation of Colloids

A few ways to prepare colloids are given below

•  Chemical method : Colloids can be prepared by chemical reactions leading to formation of molecules by double decomposition, oxidation, reduction or hydrolysis. These molecules then aggregate to form sols 

• Electrical Disintegration/ Bredig’s arc Method: This is applied to obtain colloidal sols of metals like gold, silver and platinum.  An electric arc is stuck between the electrodes of the metal immersed in the dispersion medium. The intense heat produced vapourises the metal, which then condenses to form particles of colloidal size.

• Peptization- It is the process of converting a precipitate into colloidal sol by shaking it with dispersion medium in the presence of a small amount of electrolyte. The electrolyte used for this is called peptizing agent. During peptization the precipitate absorbs the one of the ions of the electrolyte on its surface. This causes +veor –vecharge to develop on the precipitate, which ultimately break up into small particles of the size of a colloid.

Mechanism Of Micelle Formation-

• Soap is the sodium or potassium salt of fatty acid and may be represented as RCOO^- Na (e.g. sodium stearate, (CH₃(CH₂)16COO^-Na⁺]) .  Whendissolved into water , it dissociates into  RCOO^- and  Na⁺ ions

• The RCOO^-ion consists of two parts –  long hydrocarbon chain (also called  non – polar tail)  which is hydrophobic (water repelling ) and a polar group  COO^-   (polar head) which is hydrophilic (water loving )

• At higher concentrations(CMC) RCOO- ions form an aggregate of spherical shape with the hydrocarbon chains pointing towards the centre and the COO- part facing outward on the surface of the sphere. This aggregate is called ionic micelle. It may have as many as 100 ions