Why are all P-Cl bond lengths equal in PCl3 but different in PCl5?

Phosphorus atom of PCl3, is sp3 hybridised. so orbital involved in hybridization are s and p only and PCl3 has a trigonal pyramid structure.

However in case of PCl5, the hybridisation is sp3d. (sp3d, the hybridisation can represent as also sp2+pd) and it acquired TBP ( trigonal pyramidal structure).
We know that in TBP, there is two type of bond present I.e. axial (longitudinal) and equatorial bond. Bond length of axial bond is longer (coordinate bond ) while equatorial bond is shorter due to covalent nature ( formed by overlapping of atomic orbitals).

Are all bonds of If7 equivalent ?. If Not then explain ?

In IF7 seven fluorine atoms are coordinate with iodine centre, whose coordination geometry is pentagonal bipyramidal.  And hybridization is Sp3d3 but at room temperature, this structure is conformationally mobile,

 

What is "EMULSIONS"

Emulsions are colloids in which both dispersed phase and dispersion medium are liquids. 

Emulsion can be broadly classified into two types.

(i) Oil in water emulsions: In this type of emulsions, oil acts as (organic solvent) dispersed phase and water acts as dispersion medium. Some examples of this type of emulsions are milk, vanishing cream, etc. In milk, liquid fat is dispersed in water.

(ii) Water in oil emulsions: In this type of emulsions, water acts as dispersed phase and oil (organic solvent) acts as dispersion medium. Cold cream, butter etc, are examples of oil emulsions.

Identification of Emulsion 

The following tests may be employed to distinguish between the two types of emulsions:

(i) Dye test: Some oil soluble dye is added to the emulsion. If the background becomes coloured, the emulsion is water – in – oil type and if the coloured droplets are seen, the emulsion is oil – in – water type.

(ii) Dilution test: If the emulsion can be diluted with water, this indicates that water is the dispersion medium and the emulsion is of oil – in – water type. In case the added water forms a separate layer, the emulsion is water – in – oil type.

Preparation of Emulsion:

The process of making an emulsion is known as emulsification. Emulsion may be obtained by vigorously mixing both the liquids. The dispersed drops at once come together and form separate layers. To stabilize an emulsion, the addition of a small quantity of a third substance known as emulsifying agent or emulsifier is essential. Soaps and detergents are most frequently used as 

emulsifiers.

The other common stabilizing agents are proteins, gum and agar-agar.

What is application of colloids ?

Colloids including emulsions find a number of uses in our daily life and industry. Some of the uses are given below:

(i) Rubber plating: Latex is a colloidal solution of negatively charged rubber particles. Rubber plated articles are prepared by depositing negative charged particles over the article to be rubber plated by making that article an anode in a rubber plating bath.

(ii) Medicines: Medicines in colloidal form are easily absorbed by the body tissues and hence are more effective.

(iii) Sewage disposal: Colloidal particles of dirt, mud etc. carry electric charge. Hence when sewage water is passed through the plates kept at a high potential, the colloidal particles are 

coagulated due to electrophoresis and the suspended matter gets removed.

(iv) Purification of water: The precipitation of colloidal impurities present in water can be done by adding certain electrolytes like alum etc. The negatively charged colloidal particles of 

impurities get neutralized by the Al3+ ions and settle down and pure water can be decanted off.

(v) Formation of delta: River water contains charged colloidal particles of clay, sand and many other materials. Sea water is a very big store – house of a variety of electrolytes dissolved in it. As soon as river water comes in contact with sea water, the electrolytes present in sea water coagulate the suspended colloidal particles which ultimately settle down at the point of contact and thus the level of the river bed rises. As a result, water adopts a different course and delta is formed in due course of time.

(vi) Smoke screen: In warfare, smoke screens are used which are colloidal dispersion of certain 

substance in the air.

What is "peptization" ?

Peptization may be defined as 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 purpose is called peptizing agent. This method is applied, generally, to convert a freshly prepared precipitate into a colloidal sol. 

For example, when freshly precipitated Fe(OH)3 is shaken with aqueous solution of FeCl3(peptizing agent) it adsorbs Fe+3 ions and thereby breaks up into small – sized particles.