Quantum Chemistry: What is it!

We know Chemistry is the study of how atoms, molecules react in the microscopic level. On the other hand, the word ‘Quantum‘ came from ‘Quanta‘. Actually radiation is considered to be consists of particles, each such particle is called ‘Quanta‘. For light radiation, it is called ‘Photon‘.
Well, we now know what each of the words means separately. But what meaning comes out when we join both of the words? So Quantum Chemistry is that branch of chemistry which deals every physical phenomena assuming the dual nature of matter. Basically it contains pure mathematics like Calculous, Integration, Summation, Product and many other operations. 
It is interesting in the fact that we can prove and mathematically understand every physical phenomena. In some Universities, Quantum Chemistry is taught independently. But in most of the Universities, it is taught as a chapter of physical chemistry.
There is a lot more things in the universe to uncover with the help of ‘Quantum Chemistry‘.
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Amalgam Lamp: A Source of UV Radiation

Amalgam Lamp is an intense source of ultraviolet radiation (185-253.7nm) produced by an electrical discharge on a lamp with the inner side of the lamp is covered by an amalgam of mercury with indium or gallium to control the vapour pressure of mercury. These lamps are 2-3 times more efficient for the same wavelength as the standard low-pressure mercury lamp.

Amalgam Lamp

Picture Credit: Heraeus.com

Standardisation of EDTA Solution: Step by Step Process

Preparation of Standard Zinc Sulphate Solution:
Weight out about 7.18g of Zinc Sulphate heptahydrate, ZnSO4.7H2O into 250ml of volumetric flask. Make up the volume with distilled water. The solution will be about 0.1M

Preparation of EDTA Solution:

 Weigh out about 9.3g of the disodium salt of EDTA and dissolve in a 250ml volumetric flask. The solution will be about 0.1M

Procedure:

Pipette out 25ml of the Zinc Sulphate solution into a 250ml conical flask. Dilute to 100ml with distilled water and add 2ml of NH3/NH4Cl buffer solution (pH~10) and 30-50mg of Eriochrome Black T indicator. Titrate with the EDTA solution. At the end point colour changes from wine red to blue. 

Concept of Internal Energy

The energy contained in a system is called internal energy. It is denoted by U. It is the sum of following forms of energy-
(i) Kinetic energy due to translational, rotational and vibrational motion of the molecules, all of which depend on the temperature,

(ii) Potential energy due to intermolecular forces, which depends on the separation between the molecules and

(iii) Energy of the electrons and nuclei.

In practice, it is not possible to measure the total internal energy of a system in any given state. Only change of its value can be measured.

Let the state of the system is changed from an initial state 1 to final state 2; due to supply of heat Q to the system.

Let W be the work done by the system during the change, then increase in internal energy is
U2-U1 = Q-W

For ideal gas the internal energy is only the kinetic energy of its molecules. It depends on temperature and hence internal energy is the function of temperature only.

For real gas, the internal energy is the sum of kinetic energy and potential energy of the molecules due to their mutual attraction. The force of attraction between the molecules depends on the intermolecular distance and thus is a function of volume and temperature.

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Werner’s Theory of Coordination Compounds: Postulates & Discussion

Alfred Werner put forward his famous Coordination Theory to explain the formation and structure of Coordination Compounds.

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Alfred Werner

The important postulates of Werner’s Coordination Theory are-
(i) In Coordination Compounds the metal atom exhibit two types of valency, viz. Primary Valency, Secondary Valency.

The Primary Valency is ionisable and nondirectional whereas the secondary valency is nonionisable and directional. The primary valency corresponds to oxidation state and the secondary valency corresponds to the coordination number.

(ii) Every metal atom has a fixed number of secondary valency, i.e, it has a fixed coordination number.

(iii) The metal atom tends to satisfy both its primary and its secondary valencies.

Primary valencies are satisfied by negative ions whereas secondary valencies are satisfied by either negative or neutral or positive ligands.

(iv) The secondary valencies are always directed towards fixed position in space and this leads to definite geometry.

E.g., If a metal ion has six secondary valencies, these are arranged in octahedral manner around the central metal ion. If the metal ion has four secondary valency, these are arranged in either tetrahedral or square planar arrangement around the central metal ion. The secondary valencies thus determine the stereo chemistry of the compound.

The Atom Bomb: A Review

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A bomb which works in the principle of a fast nuclear chain reaction is referred to as the atomic bomb. It contains two subcritical masses or fissionable material U-235 or Pu-239.

(Subcritical Mass: If the mass of the fissionable material is less than its critical mass, nuclear fission wouldn’t occur, this system is then said to be subcritical.)

It has a mass of trinitrotoluene in a separate pocket. When TNT is detonated, it drives one mass of U-235 into the other. A supercritical mass of the fissionable material is obtained. As a result of the instantaneous chain reaction, the bomb explodes with the release of tremendous heat energy. The temperature developed in an atomic bomb believed to be 10 million degree centigrade.

Besides, many radio nuclei and heat and deadly gamma ray is released. This play havoc with life and environment. If the bomb explodes near the ground, it raises storm of dust into the air, the radioactive materials adhering to dust is known as fall out. It spreads over wide radius and as a lingering source of radioactive hazard for long periods.

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Colloids: A Brief Note

Colloids are the particles having size between 1nm to 1000nm such as H20, Alcohol, Benzene are assumed to be aggregate of many small molecules which have high molecular mass. They have the ability to scatter light and have low osmotic pressure.

Colloidal systems are divided into two parts
i. Lyophilic Colloids
ii. Lyophobic Colloids

The Lyophobic Colloids are polymeric molecules and Lyophilic Colloids are proteins or starch in water, rubber in benzene.

i. Lyophobic Colloids:
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They are solvent hating colloids. When the dispersed phase has less affinity for dispersion medium, the system is called Lyophobic Colloids.

When dispersion medium is water, they are given the name Hydrophobic. If they are separated, they can not be made by simply adding with dispersion medium.

ii. Lyophilic Colloids:

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When the dispersed phase has the highest affinity for dispersion medium, then it is called Lyophilic Colloids.

When the dispersed phase is separated from dispersion medium, they can be again made by simply remixing with the dispersion medium.

Assumptions of Langmuir Adsorption Isotherm

Irving Langmuir derived an expression for the variation in the extent of an adsorption on a solid with pressure, which is based on the following assumptions:
1. Surface of solid contains a fixed number of adsorption site, only where gaseous molecules can bind (gets adsorbed).
2. Each site can hold only one molecule and the process involves a constant heat of adsorption. This is identical for all adsorption site.
3. The adsorption is mono-layer.
4. The gaseous molecules adsorbed different adsorption site do not interact.
5. The process of adsorption involves a dynamic equilibrium.
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Electro-Organic Synthesis: A Branch of Green Chemistry

What is Electro-Organic Synthesis? 
In electro-organic synthesis, the electrodes act as “courier” of electrons. The anode which is electron deficient abstracts electron from a substrate, i.e., oxidises it and this is called Anodic oxidation, whereas the cathode which has excess of electrons can transfer an electron to the substrate i.e., reduces it and is called Cathodic reduction.
Some Advantages:
(i) Such synthesis has a green perspective as no reagent is necessary for the redox reactions- the electrons are directly exchanged between the substrate and the inert electrodes like Platinum.
(ii) Such synthesis helps in bringing about “umpolung” in the substrate and allows synthesis of compound from single substrate.
(iii) Since in electrosynthesis, the reactive species react on the electrode surface their “effective volume” is very high for which rates of the reactions are also high.
It Also Has Following Disadvantages:
(i) Multiplicities of the product are the main disadvantage.
(ii) Organic compounds are non electrolytes, i.e., non-conducting. This is overcome by adding supporting electrolytes like Li-salts or tetraalkyl ammonium salts which are appreciably soluble in organic solvents.
The reactions are usually carried out in two ways-
(i) By Potentiostatic technique (i.e. constant energy process)
In this technique the reactions become more chemo-selective and multiplicity of the product is decreased.
(ii) By Galvanostatic technique (i.e. constant current process)
This is easy to carry out but chemo-selectivity is less.

Note: Scientists claim, there is a huge potential in this field to get a Nobel Prize. Using no reagents and no chemical wastage is the main reason for this.
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Assumptions of Langmuir- Hinshelwood Mechanism: A Brief Review

Langmuir-Hinshelwood has proposed a mechanism for adsorption of gases on the surface of solid. The surface reaction is assumed to occur in the following steps:
1. Diffusion of the reactants on the surface of the solid adsorbent.
2. Adsorption of the reactants at the surface.
3. Chemical reaction at the surface.
4. Desorption of the products from the surface.
5. Diffusion of the products from the surface of the adsorbent.

Step 1 & 5 are generally very fast and step 2 & 4 are generally faster than 3. Thus step 3 is the rate determining step in the surface reaction, i.e., chemisorption of the reactants on the surface of the solid adsorbent.

Two feature of this type of surface reaction:
1. Chemisorption plays a very important role in such type of adsorption.
2. The reaction rate per unit surface area is proportional to the fraction of total surface covered with adsorbed gas molecule.

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