Monthly Archives: July 2016

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. 

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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.