If you ask what is Colloidal solutions and suspensions are, they are a mix of substances suspended in a regular pattern in a fluid. A colloid or colloidal system is a dispersion of one substance (the dispersed phase) in another (the dispersion medium), where the dispersed-phase has the same order as the medium but on a much smaller scale. At this small scale, it is believed that large particles are continuous with each other and the rest on the medium. The dispersed-phase parts of a colloid are called sols, and the medium is usually called the solvent. 

This allows some substances to dissolve in certain solvents; for example, milk and water are well known colloids whose dispersed phase (sol) is very finely divided. In the case of fog, the dispersed phase is water (liquid), while the dispersion medium is various gases. We can’t detect scattered phase particles in colloids with our naked eyes since they’re so tiny.

Colloidal systems come in three states such as liquid, solid and gas. On the other hand, a colloidal solution is considered to be a liquid mix. The size of the component parts distinguishes a genuine solution from a colloidal solution.

Colloidal solutions are created of particles that are of size from 1 nm to 500 nm, and in between is the size of real solution and colloidal suspension. In multiple cases, it is also considered a heterogeneous system and is in two phases, whereas in different states, it is called a homogenous system.  

A colloid’s particles preferentially absorb ions and gain an electric charge. A colloid’s particles all have the same charge (either positive or negative) and are hence repellent to one another. Electrophoresis is the process of charged colloidal particles moving toward an oppositely charged electrode when an electric potential is applied to them. The particles may precipitate out of the suspension if their charge is neutralised. Another colloid with oppositely charged particles can be used to precipitate a colloid. 

The particles then come together to coagulate and then spread out. The ions in saltwater precipitate the properties of a colloid silt spread in river water, making a delta; the ions in seawater precipitate the colloidal silt dispersed in river water, generating a delta.

Electric precipitators are used to remove colloidal particles (such as smoke, dust, and fly ash) from exhaust gases, according to a process invented by F. G. Cottrell.

Difference between lyophilic colloids and lyophobic colloids

 Colloidal Solution Properties

• The number of particles in a colloidal solution is smaller than the number of the given particles in the real solution, as the colloidal particles are considered huge aggregates. This results in the low order of the colligative characteristics compared to the real solution values of the same given concentrations.  

• As per the Tyndall effect, a homogeneous solution will look transparent in the dark when looked at in the light. But when it is looked at, from the right angle with the help of the right direction of light, it will look completely dark. A colloidal solution looks transparent when it is looked at with the help of the right light and right angles. But these will also have a severe to mild opalescence when it is looked at at the right angle and the passage of light. This procedure is known as the Tyndall effect, and this name is given to a bright cone of light. Since colloidal particles spread all over the direction, this becomes the same case in colloidal dispersion as well, and the light starts scattering and emphasises the course of the beam.

• The light wavelength, which is dispersed and distributed by the given particles, decides the colour of the given colloidal solution. It is the size and nature that affects the wavelength of light. 
• The colour of the colloidal solution is also determined by how the light is perceived by the observer.
• When light passes through a good mixture of milk and water, it will begin to appear blue.
• Even the finest gold sol will change colour as the particle size grows, from red to purple, blue, and finally golden.
• Under a powerful ultramicroscope, colloidal particles begin to move in a steady zig-zag pattern throughout the whole field of view in the Brownian movement.
• Brownian movement is a phenomenon that is impacted by solution, particle size, and solution viscosity, but is unaffected by colloid nature.
• The viscosity decreases as the particle size decreases.
• The faster the motion, the smaller the size and the lower the viscosity.
• Brownian movement is hypothesised to be induced by particles being beaten unevenly by molecules in the dispersion medium.
• The Brownian motion, which provides a stirring motion that prevents particles from settling, keeps sols stable.
• The particles of colloidal particles are electrically charged, always. Each particle in a colloidal solution has the same charge, which might be positive or negative.
• Colloidal particles have a charge, according to electrophoresis experiments. Colloidal particles migrate towards 1 of the 2 given electrodes of platinum submerged in a colloidal solution when a voltage difference is provided between them. The colloidal particle movement in the influence of electric potential is known as electrophoresis. The cathode attracts positively charged particles, whereas the anode attracts negatively charged ones. The medium of dispersion starts to move in the field of electricity when electrophoresis, or particle mobility, is stopped. Electroosmosis is the name for this method.
• The existence of charges on colloidal particles adds to the stability of lyophobic sols through coagulation or precipitation. If the charge of the particles is lowered in any manner, they will come together and form aggregate (or coagulate) and fall to the ground under gravity’s pull.

Conclusion:- 

The name colloid is derived from the terms colla and oids. Glue is referred to as ‘Kolla,’ while something comparable to glue is referred to as ‘Oids.’ Particles in colloidal solutions are bigger than those found in sugar or salt solutions in water, but smaller than those seen in suspensions.Colloids are widely employed in meals and the food industry. Many of the foods we consume are colloidal in nature. Cheese, milk and other dairy products are some examples.Colloidal particles have an extremely tiny size. The size of their particles ranges from 1 to 1000 nanometers.It demonstrates the Tyndall effect. It scatters the light and reflects its route across itself.Colloidal solutions are highly stable since they do not settle down when left undisturbed for a long period.Filtration will not be able to separate them.