in surface area of adsorbent. Gases like
H ,N ,CO,NH ,SO
2 2 3 2 are adsorbed on the surface of finely divided transition metals such as Ni, Co, Pt and Pd.(2) Nature of adsorbate (gas)
Easily liquefiable gases are generally adsorbed to great extent.
SO ,NH ,HCl,CO
2 3 2 are easily liquefied. Hence they are easily adsorbed.(3) Pressure of the adsorbate (gas)
In case of physisorption the gas forms monolayer at low pressure and multilayer at high pressure. Increase in pressure leads to increase in extent of adsorption.
(4) Temperature
Physisorption takes place at low temperature while chemisorption takes place at high temperature.
7.
What is colloidal solution? Give example.A. Colloidal solution contains two phases dispersed phase and dispersion medium. The continuous medium of the colloidal solution in which disperse phase particles are dispersed is dispersion medium.
Colloidal solution is a binary system in which the particle size of the dispersed phase (solute) is of the order
1mm - m1
. It is heterogeneous binary system. (1 millimicon =10
-9m)Colloidal solutions are classified into lyophilic solutions and lyophobic solutions. Lyophilic solution - Ex: Starch solution
Lyophobic solution – Ex: Gold solution
8.
Give any four differences between true solution and colloidal solutions.A. Property True solution Colloidal solution
(1) Particle size
<1mm
1mm - m1
(2) External appearance Very clear Generally clear or opaque.
(3) Nature of system Homogeneous Heterogeneous
9.
What are lyophilic colloids and lyophobic colloids?A. The colloidal solution in which the dispersed phase has great affinity with the dispersion medium is called lyophilic collidal solution.
The colloidal solution in which dispersed phase has not much affinity with the dispersion medium is called lyophobic colloid.
10.
What is emulsion? Give two examples.A. Colloidal solution in which both the dispersed phase and dispersion medium are liquids is called emulsion. Ex: Milk – fat in water emulsion; cold cream – water in fat
Both milk and cold cream are liquid in liquid type of colloid. Liquid fat is dispersed in water. Dispersed Phase: Liquid fat
Dispersion medium: Water Gold solution:
It is an aqua solution or hydro solution. It is colloidal suspension of gold particles in water. Dispersed phase: Gold particles (solid)
Dispersion medium: Water (liquid)
11.
How are emulsions classified? Give examples.A. Emulsions are classified into two classes. They are (1) Oil in water (2) water in oil (1) Oil in water (o/w) type solutions:-
In this type of emulsion the dispersed phase is oil (immiscible liquid) and the dispersion medium is water. Ex: Milk, Vanishing cream
(2) Water in oil (w/o) type emulsion:- In this type of emulsion the dispersed phase is water and the dispersion medium is oil (immiscible liquid)
Ex: Stiff greases: Water in lubrication oils ; Cold liver oil: Water in cod liver oil
12.
Explain the cleaning action of soap.A. Clothes which are to be washed contain greeze or fat adhered to cloth called dirt.
In cleaning process dirt forms an emulsion with water which is used for cleaning. This emulsion is not stable, it is stabilized by converting the dirt into micelle by the soap. Soap dissolves in water and gives
Na
+ and stearate ions containing hydrophobic end (alkyl group end). This is the tail part of anion. The stearate ion also contain hydrophilic end(
COO
-)
. This is called head part of anion. The tail part dissolves the dirt and forms micelle and this micelle is removed by water in the cleaning process.13.
What is catalyst? Give two examples.A. A catalyst is the substance that increase the rate of a chemical reaction to which it is added without itself being consumed in the reaction.
Ni 2 Catalyst 4 2
CO 3H+
¾¾¾¾®CH
+H O
Cu 2 CatalystCO H+
¾¾¾¾®HCHO
14.
How is catalysis classified? Give examples.A. Catalysis is classified into two types based on the physical state (phase) of the catalyst and the reactant. They are homogeneous and heterogeneous catalyst.
Homogeneous catalysis: In both the reactants and catalyst are present in same phase then it is called homogeneous catalysis.
Ex:
2SO
2 g( )+O
2 g( )¾¾¾¾
NO( )g®2SO
3 g( )
( )
g 2 g( )
NO( )g 2 g( )
2CO
+O
¾¾¾¾®2CO
Heterogeneous catalysis: If the reactant and catalyst are present in different phases it is called heterogeneous catalysis.
( )
( )
Pt( )s( )
2 g 2 g 3 g
2SO
+O
‡ˆˆˆˆˆˆˆˆ†2SO
15.
What is autocatalysis? Give two examples.A. In a reaction if one of the intermediate product formed itself functions as catalyst it is called autocatalysis. Ex: (1)
2KMnO
4+5H C O
2 2 4+3H SO
2 4®2MnSO
4+K SO
2 4+8H O 10CO
2+
24
MnSO
formed acts as autocatalyst. (2)2AsH
3®2As 3H+
2As formed functions as autocatalyst.
16.
What is tyndall effect? Explain.A. It is an optical property. When light enters a colloidal solution, it is scattered by the large sized colloidal particles. When light passes through a solution we will be able to see the path of the light as luminous beam. This is called tyndal effect. This luminescent path can be viewed through a microscope placed at right angles to the direction of the path of the light. The bright come of light is tyndall cone. Tyndall effect is observed when
(1) The diameter of dispersed particles is not much smaller than the wavelength of light used and (2) The refractive indices of the dispersed phase and dispersion medium differ greatly in magnitude.
17.
What is coagulation? Write about Hardy-Schulze law.A. The phenomenon of colloidal substance loosing charge and coming down as a precipitate on addition of an electrolyte is called coagulation or flocculation.
The effectiveness of an ion or electrolyte in causing coagulation is dependent on the sign of the charge and magnitude of charge. This fact is explained by Hardy and Schulze. Hence the law or rule is known as Hardy- Schulze rule.
Hardy Schulze Law
The ion with charge opposite to the charge of the colloid particle is effective in coagulating the colloid. Greater the charge of the ion greater is the coagulating ability of the ion.
Positive colloids are coagulated by negative ions or anions of the salt added.
2 3
4 4
Cl
-<SO
-<PO
-Negative colloide are coagulated by positive ions or cations of the salt added.
2 3
K
+<Ba
+<Al
+18.
What is Brownian movement?A. Robert Brown observed that pollen grains when suspended in a liquid and absorbed under microscope show random motion of pollen grains. This type of motion is known as Brownian movement. All colloidal particles in colloidal solution exhibit this type of motion. The motion becomes less vigorous as the size of the particle increases and also with the viscocity of the dispersion medium but increases with rise in temperature.