Online Notes on chapter => 5 (Surface Chemistry) PART 2

These are Online Notes  PART 2  on Chapter => 5 (Surface Chemistry) 
For Practice of  CBSE Board, CBSE NEET, CSIR NET etc.

21. Enzymes: Enzymes are complex nitrogenous organic compounds which
are produced by living plants and animals. They are actually protein
molecules of high molecular mass. They are biochemical catalysts

22. Steps of enzyme catalysis:

(i) Binding of enzyme to substrate to form an activated complex
E   +    S    ==>   ES*

ii) Decomposition of the activated complex to form product
ES*   ==>  E  +  P

23.Characteristics of enzyme catalysis:

i) They are highly efficient. One molecule of an enzyme can transform 106 molecules of reactants per minute.

ii) They are highly specific in nature, e.g., urease catalysis hydrolysis of urea only.

iii) They are active at optimum temperature (298 – 310 K). The rate of enzyme catalysed reaction becomes maximum at a definite temperature called the optimum temperature.

iv) They are highly active at a specific pH called optimum pH.

v) Enzymatic activity can be increased in presence of coenzymes which can be called as promoters.

vi) Activators are generally metal ions Na⁺, Co²⁺ and Cu²⁺ etc. They weakly bind to enzyme and increase its activity.

vii) Influence of inhibitors (poison): Enzymes can also be inhibited or poisoned by the presence of certain substances.

24. Distinction between true solution, colloids and Suspension.

True solution	Colloids	Suspension
It is homogeneous	It appears to be	It is heterogeneous
	homogeneous but is
	actually heterogeneous
The diameter of the	The diameter of the	The diameter of the
particles is less than 1	particles is 1 nm to	particles are larger that
nm	1000 nm	1000 nm
It passes through filter	It passes through	It does not pass through
paper	ordinary filter paper but	filter paper
	not through ultra-filters
Its particles cannot be	Its particles can be seen	Its particles can be seen
seen under a	by a powerful	even with naked eye
microscope	microscope due to
	scattering of light

25. Colloids: A colloid is a heterogeneous system in which one substance is
dispersed as very fine particles in another substance called dispersed
medium.

26. Dispersed phase: The substance which is dispersed as very fine
particles is called dispersed phase.

27. Dispersion medium: The substance present in larger quantity is called
dispersion medium.

28. Classification of colloids on the basis of the physical state of dispersed
phase and dispersion medium:

Dispersed	Dispersion	Name	Examples
phase	medium
Solid	Gas	Aerosol	Smoke, dust
Solid	Liquid	Sol	Paints
Solid	Solid	Solid sol	Coloured gem tones
Liquid	Solid	Gel	Jellies, cheese
Liquid	Liquid	Emulsion	Milk, hair cream
Liquid	Gas	Aerosol	Fog, mist, cloud
Gas	Solid	Solid sol	Pumice stone, foam
			rubber
Gas	Liquid	Foam	Whipped cream,
			froth

29. Classification of colloids on the basis of nature of interaction between
dispersed phase and dispersion medium :

Lyophobic sols	Lyophilic sols
These colloids are liquid hating.	These colloids are liquid loving.
In these colloids the particles of	In these colloids, the particles of
dispersed phase have no affinity	dispersed phase have great
for the dispersion medium.	affinity for the dispersion medium.
They are not stable.	They are stable.
They can be prepared by mixing	They cannot be prepared by
substances directly.	mixing substances directly. They
	are prepared only by special
	methods

They need stabilizing agents for	They do not need stabilizing
their preservation.	agents for their preservation.
They are irreversible sols.	They are reversible sols.

30. Classification of colloids on the basis of types of particles of the
dispersed phase:

a. Multimolecular colloids: The colloids in which the colloidal
particles consist of aggregates of atoms or small molecules. The
diameter of the colloidal particle formed is less than 1 nm.

b. Macromolecular colloids: These are the colloids in which the
dispersed particles are themselves large molecules (usually
polymers). Since these molecules have dimensions comparable
to those of colloids particles, their dispersions are called
macromolecular colloids, e.g., proteins, starch and cellulose
form macromolecular colloids.

c. Associated colloids (Micelles): Those colloids which behave as
normal, strong electrolytes at low concentrations, but show
colloidal properties at higher concentrations due to the
formation of aggregated particles of colloidal dimensions. Such
substances are also referred to as associated colloids.

31. Kraft Temperature (T_k): Micelles are formed only above a certain
temperature called Kraft temperature.

32. Critical Micelle Concentration (CMC): Micelles are formed only above a
particular concentration called critical micelle concentration.

33. Soaps: Soaps are sodium or potassium salts of higher fatty acids e.g., sodium stearate CH₃(CH₂)₁₆COO^-Na⁺

34. Methods of preparation of colloids:

a. Chemical methods: Colloids can be prepared by chemical reactions leading to the formation of molecules. These molecules aggregate leading to formation of sols.

b. Electrical disintegration or Bredig’s Arc method: In this method, electric arc is struck between electrodes of the metal immersed 9 in the dispersion medium. The intense heat produced vaporizes the metal which then condenses to form particles of colloidal size.

c. 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.

35.Purification of colloids:

a. Dialysis: It is a process of removing a dissolved substance from a Colloidal solution by means of diffusion through a suitable membrane.

b. Electro dialysis: The process of dialysis is quite slow. It can be made faster by applying an electric field if the dissolved substance in the impure colloidal solution is only an electrolyte.

c. Ultrafiltration: Ultrafiltration is the process of separating the colloidal particles from the solvent and soluble solutes present in the colloidal solution by specially prepared filters, which are permeable to all substances except the colloidal particles.

d. Ultracentrifugation: In this process, the colloidal solution is taken in a tube which is placed in ultracentrifuge. On rotating the tube at very high speed, the colloidal particles settle down at the bottom of the tube and the impurities remain in solution. The settled particles are mixed with dispersion medium to regenerate the sol.

36. Properties of colloids:

a. Colour: The colour of colloidal solution depends upon the wavelength of light scattered by the colloidal particles which in turn depends upon the nature and size of particles. The colour also depends upon the manner in which light is received by the observer.

b. Brownian movement: Colloidal particles move in zig – zag path. This type of motion is due to colliding molecules of dispersion medium constantly with colloidal particles.

c. Colligative properties: The values of colligative properties (osmotic pressure, lowering in vapour pressure, depression in freezing point and elevation in boiling point) are of small order as compared to values shown by true solutions at the same concentrations.

d. Tyndall effect: The scattering of a beam of light by colloidal particles is called Tyndall effect. The bright cone of light is called the Tyndall cone.

e. Charge on colloidal particles: Colloidal particles always carry an electric charge. The nature of this charge is the same on all the particles in a given colloidal solution and may be either positive or negative. 

Positively charged colloids	Negatively charged colloids
Hydrated metallic oxides such as	Metallic sulphides like As2S3, Sb2S3
Fe2O3.xH2O, Cr2O3.xH2O, Al2O3.xH2O	sols
Basic dye stuff like malachite green,	Acid dye stuff like eosin, methyl
methylene blue sols	orange, Congo red sols
Haemoglobin (blood)	Starch sol, gum, gelatin, clay,
	charcoal, egg albumin, etc.

f. Helmholtz electrical double layer: When the colloidal particles cquire negative or positive charge by selective adsorption of one of the ions, it attracts counter ions from the medium forming a second layer. The combination of these two layers of opposite charges around colloidal particles is called Helmholtz
electrical double layer.

g. Electrokinetic potential or zeta potential: The potential difference between the fixed layer and the diffused layer of opposite charges is called electrokinetic potential or zeta potential.

h. Electrophoresis: The movement of colloidal particles under an applied electric potential is called electrophoresis.

i. Coagulation or precipitation: The process of settling of colloidal particles as precipitate is called coagulation.

Hardy – Schulze rules:

i) Oppositely charged ions are effective for coagulation.

ii) The coagulating power of electrolyte increases with increase in charge on the ions used for coagulation, e.g. Al³⁺ > Ba²⁺ > Na⁺ for negatively charged colloids. [Fe (CN)₆]^4- > PO₄ ^3- > SO₄ ^2- > Cl ^- for positively charged colloids

37.Types of emulsions:

a. Water dispersed in oil: When water is the dispersed phase and oil is
the dispersion medium. E.g. butter

b. Oil dispersed in water: When oil is the dispersed phase and water is
the dispersion medium. E.g. milk

38.Emulsification: The process of stabilizing an emulsion by means of an
emulsifier.

39.Emulsifying agent: The substances which are added to stabilize the
emulsions are called emulsifying agents or emulsifiers. E.g. soaps,
gum

40. Demulsification: The process of breaking an emulsion into its
constituent liquids is called demulsification by freezing, boiling,
centrifugation or some chemical methods.

Click HERE For "Surface Chemistry" Notes "PART 1"