--%>
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 : Problem based on molarity Select the

    Select the right answer of the question. If 18 gm of glucose (C6H12O6) is present in 1000 gm of an aqueous solution of glucose, it is said to be: (a)1 molal (b)1.1 molal (c)0.5 molal (d)0.1 molal

    		•
  • Q : Molar conductance what is the molar

    what is the molar conductance of chloropentaamminecobalt(III) chloride?

    		•
  • Q : Basicity order order of decreasing

    order of decreasing basicity of urea and its substituents

    		•
  • Q : Explain the process of adsorption in

    The process of adsorption can occurs in solutions also. This implies that the solid surfaces can also adsorb solutes from solutions. Some clarifying examples are listed below: (i) When an aqueous solution of ethano

    		•
  • Q : Concentration of urea Help me to go

    Help me to go through this problem. 6.02x 1020 molecules of urea are present in 100 ml of its solution. The concentration of urea solution is: (a) 0.02 M (b) 0.01 M (c) 0.001 M (d) 0.1 M (Avogadro constant, N4= 6.02x 1023mol -1)<

    		•
  • Q : Define Virial Equation The constant of

    The constant of vander Waal's equation can be related to the coefficients of the virial equation.  Vander Waal's equation provides a good overall description of the real gas PVT behaviour. Now let us

    		•
  • Q : Biodegradable polymers what are the

    what are the examples of biodegradable polymers

    		•
  • Q : Liquid Vapour Free Energies The free

    The free energy of a component of a liquid solution is equal to its free energy in the equilibrium vapour.Partial molal free energies let us deal with the free energy of the components of a solution. We use these free energies, or simpler concentration ter

    		•
  • Q : What type of bond does HCl encompass

    What type of bond does HCl encompass? Describe briefly?

    		•
  • Q : What are halogen oxoacids? Fluorine

    Fluorine yields only one oxyacid, hypo

    		•