CRYSTALLIZATION WITH PRESENTATION

 

CRYSTALLIZATION

ü  What is “CRYSTALLIZATION”

ü  Crystallization Definition

ü  Crystallization Processes

ü  Mechanism Of Crystallization

 

What Is “CRYSTALLIZATION”?

›  Crystallization, or crystallisation, is the process of atoms or molecules arranging into a well-defined, rigid crystal lattice in order to minimize their energetic state. The smallest entity of crystal lattice is called a unit cell, which can accept atoms or molecules to grow a macroscopic crystal. During crystallization, atoms and molecules bind together with well-defined angles to form a characteristic crystal shape with smooth surfaces and facets. Although crystallization can occur in nature, crystallization also has a broad industrial application as a separation and purification step in the pharmaceutical and chemical industries

 *Crystal lattice is the symmetrical three-dimensional structural arrangements of atoms, ions or molecules (constituent particles) inside a crystalline solid as points. It can be defined as the geometrical arrangement of the atoms, ions or molecules of the crystalline solid as points in space

 

Crystallization Definition

›  Key Crystallization Definitions

›  Solubility
Solubility is a measure of the amount of solute that can be dissolved in a given solvent at a given temperature

›  Saturated Solution
At a given temperature, there is a maximum amount of solute that can be dissolved in the solvent. At this point, the solution is saturated. The quantity of solute dissolved at this point is the solubility.

›  Supersaturation
Supersaturation can mean the status that the actual solute concentration is higher than the equilibrium solute concentration (solubility), or the degree of how much the concentration is higher than the solubility.

 

CRYSTALLIZATION PROCESSES:

Cooling Crystallization

The cooling crystallization can be applied when the solubility gradient of the solution increases steeply with falling temperature or when vaporization of the solvent has to be avoided.

 

Evaporative Crystallization:

Generating crystals by evaporating a solution at a constant temperature

 

MECHANISM OF CRYSTALLIZATION:

›  MECHANISM OF CRYSTALLIZATION: Three major steps are involved in crystallization: 1. Super Saturation. 2. Nucleation. 3. Crystal Growth.

›  1. Super Saturation of the solution: A solution is saturated when the crystallization and solvation are at equilibrium. Solutions can be heated to create supersaturated solutions. Supersaturations are created by adding heat to a saturated solution and more solute. The solute is able to solvate with the added heat. A properly made supersaturated solution will remain solvated as the solution cools to room temperature.

 

MECHANISM OF CRYSTALLIZATION:

›  2. Nucleation: Nucleation, the initial process that occurs in the formation of a crystal from a solution, a liquid, or a vapour, in which a small number of ions, atoms, or molecules become arranged in a pattern characteristic of a crystalline solid, forming a site upon which additional particles are deposited as the crystal grows.

›  Nucleation of ice crystals:

Before ice can form, water must supercool and ice crystals nucleate. Homogeneous nucleation (without the influence of foreign particles) occurs well below the freezing point, at temperatures that are not observed in water bodies. The temperature of heterogeneous nucleation(nucleation beginning at the surface of foreign particles) depends on the nature of the particles, but it is generally several degrees below the freezing point.

 

MECHANISM OF CRYSTALLIZATION:

›  Crystal Growth:. Crystal growth is a major stage of a crystallization process and consists in the addition of new atoms, ions, or polymer strings into the characteristic arrangement of the crystalline lattice

 

Crystallization As A Purification Process

Ø  Crystals are the purest form of geometrical shapes. The process by which an impure compound is converted into crystals is called crystallization.

Ø  This is one of the most commonly used techniques for the purification of inorganic/organic solids.

Ø  This is based upon the principle that when a crystal is formed, it tends to exclude the impurities which remain in the solution.

Ø  Let us explain the process of crystallization by taking the example of the purification of impure copper sulphate.

 

Crystallization As A Purification Process

1. Take about 5g of impure copper sulphate and dissolve it in a minimum amount of water in a china dish.
2. The solution is then filtered to remove insoluble and suspended impurities.
3. Therefore, the filtrate is evaporated in a china dish so as to get a saturated solution.
4. The hot saturated solution thus obtained is allowed to stand undisturbed for a few hours when crystals of pure Copper sulphate separate out.
5. These crystals are separated by filtration through an ordinary funnel and the filtrate left after the separation crystals are called the mother liquor.

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