--%>
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 : Questuion associated with colligative

    Provide solution of this question. Which of the following is a colligative property: (a) Surface tension (b) Viscosity (c) Osmotic pressure (d) Optical rotation

    		•
  • Q : Normality of solution containing

    Can someone please help me in getting through this problem. Determine the normality of a solution having 4.9 gm H3PO4 dissolved in 500 ml water: (a) 0.3  (b) 1.0  (c) 3.0   (d) 0.1

    		•
  • Q : Calculating molarity of a solution

    Select the right answer of the question .The molarity of a 0.2 N N2Co3 solution will be: (a) 0.05 M (b) 0.2 M (c) 0.1 M (d)0.4 M

    		•
  • Q : Explain the process of coagulation of

    Presence of small concentrations of appropriate electrolyte is necessary to stabilize the colloidal solutions. However, if the electrolytes are present in higher concentration, then the ions of the electrolyte neutralize the charge on the colloidal particles may unite

    		•
  • Q : What is Spectroscopy? This is a very

    This is a very important aspect of Physical Chemistry in which knowledge of the size, shape, rigidity and electronic structure of molecules deduced from the experimental methods treated here goes hand in hand with the theoretical approaches of chemical reactions. Spec

    		•
  • Q : Molarity of solution Help me to go

    Help me to go through this problem. When 7.1gm Na2SO4 (molecular mass 142) dissolves in 100ml H2O , the molarity of the solution is: (a) 2.0 M (b) 1.0 M (c) 0.5 M (d) 0.05 M

    		•
  • Q : Problem on partial pressure i) Show

    i) Show that the equilibrium constant Kp for the reaction CaCo3(s) ↔ CaO(s) +CO2(g)is about unity (i.e. = 1.0) at 895 °C.ii) If two grams of calcium carbonate are pl

    		•
  • Q : Explain the mechanism of Enzyme

    A mechanism for enzyme-catalyzed reactions that leads to the typical rate equation for these reactions can be described.A variety of rate equations are required to portray the rates of enzymes catalyzed reagents and physical conditions that are encountered

    		•
  • Q : Organic and inorganic substances living

    living beings are made up of organic and inorganic substances.according to their complexity of their molecules how can ach of these substances be classified?

    		•
  • Q : Alkaline medium The amount of KMnO 4

    The amount of KMnO4 required to prepare 100 ml of 0.1N solution in alkaline medium is: (a) 1.58 gm (b) 3.16 gm (c) 0.52 gm (d) 0.31 gmAnswer: (a) In alkaline medium KMnO4 act as ox

    		•