--%>
Assignment Help - homework help

Explain polyhalogen compounds with examples.

Carbon compounds containing more than one halogen atom are called polyhalogen compounds. Most of these compounds are valuable in industry and agriculture. Some important polyhalogen compounds are described as follows:

    
Dichloromethane or methylene chloride, CH3Cl2

Dichloromethane is prepared industrially by direct chlorination of methane. The mixture of CH3Cl, CH2Cl2, CHCl2 and CCl4 so obtained is separated by fractional distillation.

Properties

Dichloromethane is a sweet smelling volatile liquid and its boiling point is 313 K.

Dichloromethane harms the human central nervous system. Exposure to lower levels of dichloromethane in air can lead to slightly impaired hearing and vision. Higher levels of dichloromethane in air can cause dizziness, nauses and numbness in the fingers and toes. Direct skin contact with methylene chloride causes strong burning and mild redness to the skin. Direct contact with eyes can burn cornea.

Uses
    
Because of its low boiling point and low inflammability it is used as extraction solvent in pharmaceutical and food industries. It is also used as solvent for carrying out many organic reactions in research laboratories.
    
It is used as a metal finishing and cleaning solvent.
    
It is also used as a propellent in aerosols.
    
Trichloromethane (Chloroform), CHCl3 

Preparation
    
From methane: chloroform is manufactured by chlorination of methane in the presence of light or catalysts.
1278_polyhalogen compounds.png                                     


The mixture of CH3Cl, CH2Cl2, CHCl3 and CCl4 can be separated by fractional distillation.
    
From chloral hydrate, pure chloroform can be obtained by distilling chloral or chloral hydrate with concentrated aqueous solution or KOH solution.
                    
NaOH + CCl3CHO  1950_electrode potential.png  HCOONa + CHCl2
             
NaOH + CCl3CH(OH)2  1950_electrode potential.png  HCOOna + CHCl3 + H2O
    
Laboratory method: in this method chloroform is obtained from ethanol or acetone by reaction with a paste of bleaching powder and water.

In this reaction, bleaching powder serves as a source of chlorine which first oxidizes ethanol acetaldehyte, which is then further chlorinated to chloral. Chloral reacts with Ca(OH)2, given by CaOCl2, to give chloroform and calcium formate.

   Related Questions in Chemistry

  • Q : Molarity of acid solution If 20ml of

    If 20ml of 0.4N, NaoH solution completely neutralises 40ml of a dibasic acid. The molarity of the acid solution is: (a) 0.1M (b) 0.2M  (c) 0.3M (d) 0.4M Choose the right answer fron above.

    		•
  • Q : Problem on Clausius equation of state

    If a gas can be described by the Clausius equation of state: P (V-b) = RT Where b is a constant, then:  (a) Obtain an expression for the residual vo

    		•
  • Q : What is cannizaro reaction? Explain

    Aldehydes which do not have  -hydrogen atom, such as formaldehyte and benzaldehyte, when heated with concentrated (50%)alkali solutio

    		•
  • Q : Mole fraction of Carbon dioxide Choose

    Choose the right answer from following. If we take 44g of CO2 and 14g of N2 what will be mole fraction of CO2 in the mixture: (a) 1/5 (b) 1/3 (c) 2/3 (d) 1/4

    		•
  • Q : Dissolving Group IV Carbonate Explain

    Explain how dissolving the Group IV carbonate precipitate with 6M CH3COOH, followed by the addition of extra acetic acid.

    		•
  • Q : Solution density of water is 1g/mL.The

    density of water is 1g/mL.The concentration of water in mol/litre is

    		•
  • Q : Molecular Properties Symmetry Molecular

    Molecular orbitals and molecular motions belong to certain symmetry species of the point group of the molecule.Examples of the special ways in which vectors or functions can be affected by symmetry operations are illustrated here. All wave functions soluti

    		•
  • Q : Explain the polymers and its types.

    Polymers are the chief products of modern chemical industry which form the backbone of present society. Daily life without the discovery and varied applications of polymers would not have been easier and colourful. The materials made of polymers find multifarious uses and applications in all walk

    		•
  • Q : Why acetic has less conductivity than

    Illustrate the reason, why acetic has less conductivity than Hcl?

    		•
  • Q : What is Flash Photolysis Reactions.

    An example illustrates the type of mechanism that can be written to explain the development of flash photolysis reactions. Often, as the reactions in the ozone layer of the earth's atmosphere, we are interested in the kinetic behavior of species that are not a

    		•