Crystallisation - class-VII

A chemical change is a process where one or more substances are converted into one or more new substances. Examples: Explosion of fireworks that produces heat, light, sound and unpleasant gases, breaking down of ozone in the ozone layer by the UV radiations.

When a substance undergoes chemical change, its chemical properties are altered.

In whipping of eggs, the air is introduced into the fluid but no new substance is formed. Hence, it is a physical change. Digestion and burning of wood results in the formation of new substances. Thus, it is a physical change.

Burning of candle is a chemical change because the wax gets converted into carbon dioxide whereas the rest of the options represent the physical change.

Heating is the process of increasing the temperature of a body from its original temperature.

Crystals contain water of crystallization hence during formation of crystals water of crystallization should not be evaporated.

Crystallization is a process of formation of solid crystals in a homogenous solution. Thus it is a physical process and not a chemical process.

One more new substances one formed in a chemical change. The new substances formed have properties different from those of the reacting substances. A chemical change is always accompanied by the absorption or evolution of energy in the form of heat, light or sound.

Sun tanning is a chemical change as vitamin D and melanin are produced during tanning. As new products are formed during sun tanning, it is considered to be a chemical change.

Exothermic reactions are usually uncatalyzed and spontaneous. They are chemical reactions that release energy by light or heat. Energy is emitted out.

One of the most common solvents is water. It is also called as a universal solvent.

It is known as crystallization - because salt is obtained in crystal form.

Crystalisation takes place by the process of vaporization.

In crystalline solids, the atoms, ions or molecules are arranged in an ordered and symmetrical pattern that is repeated over the entire crystal. The smallest repeating structure of a solid is called a unit cell, which is periodically repeated in three dimensions on a lattice.

The most common solvent used in crystallization is water, it does not dissolve the substance to be purified at room temperature, but it dissolves it well at solvent's boiling point, and dissolves soluble impurities well at room temperature.
Water is capable of dissolving a variety of different substances than any other liquid and is called the universal solvent.

The solvent dissolves a large amount of solute at boiling temperature, i.e an increase in temperature increases the solubility of the solute. As the temperature increases, the particles of the solid move faster which increases the chances that they will interact more with the solvent molecules. As the temperature increases, the amount of solute that can be dissolved in a solvent increases generally is high at their individual boiling points.

Desiccators are an economical and reliable way to assure dry, dust-free storage and organization of humidity sensitive products valuable reagents in crystalline form. Proper storage conditions can be optimized by selecting a desiccator size, shape and control mechanism best suited for the application.
The lower compartment of the desiccator contains lumps of silica gel, anhydrous calcium chloride to absorb water vapor. The substance needing the desiccation is put in the upper compartment, on a glazed perforated ceramic plate. The ground glass rim of the desiccator lid must be greased with a thin layer of vacuum grease. 

Phenolphthalein [3,3-Bis (4- hydroxyphenyl)- 2 benzofuran- 1-one] is often used as an indicator in acid-base titrations. It turns colourless in acidic solutions and pink in basic solutions.

Phenolphthalein [3,3-Bis (4- hydroxyphenyl) - 2 benzofuran- 1-one] is often used as an indicator in acid-base titrations. It turns colourless in acidic solutions and pink in basic solutions. Phenolphthalein is slightly soluble in water and usually dissolved in alcohols for use in experiments. It is a weak acid which can loose $H^{+}$ ions in solution. Phenolphthalein molecule is colourless and phenolphthalein ion is pink in colour. When a base is added to phenolphthalein, the molecule turns in to ions leading to more ionization as $ H^{+} $ ions are removed.

The option (A) represents correct statements.
Salt can be obtained by the evaporation of sea water.
The salt obtained during crystallisation is not pure and its crystals are small.
After crystallisation, the shape of the crystals cannot be seen clearly.
Large crystals of pure substances can be formed from their solutions.

On evaporation of seawater in shallow pools, salt along with impurities remain behind. Impured salt is taken in a tank and its saturated solution is prepared. In a saturated solution of salt, HCl vapours are passed. Chloride ions being common to both, it's concentration increases, and NaCl gets precipitated which is free from impurities.

The process of forming large crystals of pure substances from their solutions is known as Crystallization. The principle of crystallization is concerned with the thermodynamic conditions of crystallization and the kinetics of crystal nucleation and growth.
Crystallization is the physical transformation of a liquid solution or gas to a crystal which is a solid with an ordered internal arrangement of molecules, ions or atoms.

The process of formation of solid crystals from a homogeneous solution is called crystallization. It is a physical change. Crystallization is the solidification of atoms or molecules into a highly structured form called a crystal. It can also refer to the solid-liquid separation and purification technique in which mass transfer occurs from a liquid solution to a pure solid crystalline phase.

Phenolphthalein [3,3-Bis (4- hydroxyphenyl)- 2 benzofuran- 1-one] is often used as an indicator in acid-base titrations. It turns colourless in acidic solutions and pink in basic solutions. Phenolphthalein is slightly soluble in water and usually dissolved in alcohols for use in experiments. It is a weak acid which can loose $H^{+}$ ions in solution.