ADSORPTION INDICATORS

 ADSORPTION INDICATORS:

Titration is a method of determining the concentration of an unknown solute using a known concentration solution. In which a titrant is usually applied from a burette to a known compound volume until the reaction is complete, the endpoint is detected using an indicator.

Ex: Acid-base titration, redox titration, precipitation titration, and complexometric titration.

 What is precipitation titration? 

Precipitation titration is a type of titration in which the titration reaction formed a precipitate. The titrant reacts with the compound to produce an insoluble substance (precipitate). The basic principle of precipitation titrations is that the amount of precipitating reagent or precipitant added is equivalent to the substance being precipitated. 

Amount of added precipitating agent = the amount of a compound that is precipitated 

What is Fajan’s method in chemistry?  

The Fajans method is an analytical technique that uses adsorption to detect halide content. It is commonly used to quantitatively analysis of halide ions or thiocyanate ions.  This method uses a dichlorofluorescein indicator. 

Cl– ions titration using AgN03 in the presence of an adsorption indicator, in which, AgN03 is filled in a burette, and Cl– ion solution with indicator is added in a conical flask. The titration reaction would be

Ag+ + Cl− ⇌ AgCl(s)

Colloidal particles are formed by silver chloride. Because of the adsorption of excess Cl- to the surface of the precipitant particles before the equivalence point, the surface of the precipitant particles will be negatively charged.

The dye dichlorofluorescein can be used as an indicator to determine chloride in Fajan's titration, by which the endpoint is detected by the green suspension turning pink. The dye dichlorofluorescein can be used as an indicator to determine chloride in Fajan's titration, by which the endpoint is detected by the green suspension turning pink.

The mechanism of indicators action:

 The best–known adsorption indicator is fluorescein, which is used to indicate the equivalence point in the titration of Cl- with Ag+ . Fluorescein is a weak acid, which partially dissociates in water to form fluoresceinate anion.

The fluoresceinate anion has a yellow–green colour in solution.  When Cl is titrated with Ag+ in the presence of fluorescein, the negatively charged fluoresceinate anions are initially repelled by the negatively charged AgCl colloidal particles, with their primary adsorption layer of Cl ions.  Thus the fluorescein remains in a yellow–green colour prior to the equivalence point.  At the equivalence point, the colloidal AgCl particles undergo an abrupt change from a negative charge to a positive charge by virtue of Ag+ ions adsorbed in the primary adsorption layer.  The fluoresceinate ions are strongly adsorbed in the counter–ion layer of the AgCl colloids, giving these particles a red colour and providing an end point colour change from yellow–green to red or pink. 

SYMMETRY

The term symmetry is derived from the Greek word “symmetria” which means “measured together”. An object is said to be symmetric if one part (e.g. one side) of it is the same as all of the other parts.

Symmetry is a  geometrical property of the world in which we live. In nature many type of flowers and plants, insects, certain fruits vegetables and various microscopic organism exhibit  symmetry.

Symmetry concepts are extremely useful in Chemistry. On the basis of symmetry we can predict infrared spectra, predict the optical activity and interpret electronic spectra and study of molecular properties. Symmetry helps us understand molecular structure, some chemical properties, and physical properties.

Symmetry Operations and Symmetry Elements

A symmetry operation is an operation on a body such that, after the operation has been carried out, the result is indistinguishable from the original body. ie, A symmetry operation is the action that produces an object identical to the initial object.

Elements of symmetry offer a simple device to decide whether a molecule is chiral or achiral, i.e., whether it is superimposable on its mirror image or not.

 Hi Student Friends,

Here is another post that discuss about co-Fajan-s-Rulevalency in ionic compound

Fajan's Rule by Jim Livingston on Scribd

Fajan’s rule

Fajans’ rule predicts whether a chemical bond will be covalent or ionic. A few ionic bonds have partial covalent characteristics which were first discussed by Kazimierz Fajans in 1923. 

Postulates of Fajans’ Rule

The rule can be stated on the basis of three factors, which are:

1. Size of the ion: Smaller the size of cation, the larger the size of the anion, greater is the covalent character of the ionic bond.
2. The charge of Cation: Greater the charge of cation, greater is the covalent character of the ionic bond.
3. Electronic configuration: For cations with same charge and size, the one, with (n-1)dn nso which is found in transition elements have greater covalent character than the cation with ns2 np6 electronic configuration, which is commonly found in alkali or alkaline earth metals.

Explanation of Fajans’ Rule

Here is the explanation of Fajans’ rules:
Rule 1: It is about the polarising power of the cation. When the cation is smaller, the charge density of the ion will be high and the polarizing power of the ion will be high this makes the compound to be more covalent.

Rule 2: The second rule is about the polarizability of the anion. Since in the large aions the electron is loosely bonded, it can easily be polarized by an anion. It can easily be polarized by a cation thereby making the compound more and more covalent.  

Rule 3: If we want to find the more covalent compound among HgCl2 and Calcium Chloride we cannot use size as a factor to conclude. This is because both Hg2+ and Ca2+ are of almost equal size. To explain this, we employ the third rule. The electronic configuration of Hg2+ is 6s0 5d10. This configuration is called pseudo-octet because d-orbital is fully filled, but the element does not have 8 electrons or an octet. We know that d orbitals are not good at shielding, so we can say that the anion (Cl–) would be more polarised because the d orbital is poor at shielding making HgCl2 more covalent than CaCl2 because Ca2+ ion has a noble gas configuration.

IS THERE ANY RELATION BETWEEN CURTIUS REARRANGEMENT AND HEART FAILURE ??

Spectroscopy II

IR Spectroscopy

Infrared Spectroscopy by Jim Livingston on Scribd

Spectroscopy

Spectroscopy - I

Dear friends

Welcome back.

After a long back I am posting here. This post is about spectroscopy.

Spectroscopy I by Jim Livingston on Scribd

DETERGENTS

Dear Friends, 

This post is exclusively for detergents and its types. Though this post does not discuss in detail about detergents it will help you to understand about how it differs from soap. 

Detergents by Jim Livingston on Scribd