Chemistry XI Content

General
Organic Chemistry
Nomenclature of Organic Compounds
Introduction to Hydrocarbons
An Introduction to Benzene
Alkyl Halides
Inorganic Chemistry
Physical Chemistry
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Ethyne

CHEMISTRY OF ETHYNE
INTRODUCTION
 Molecular formula = C2H2
Empirical formula = CH
Molecular mass = 26
Empirical mass = 13
Common name = Acetylene
Homologous series = Alkynes
ORBITAL STRUCTURE
OF ETHYNE
   COMPOSITION OF ETHYNE MOLECULE:
Ethyne molecule consists of two C-atoms and two H-atoms (C2H2).
 NATURE OF HYBRIDIZATION:
In ethyne molecule, each carbon atom is Sp-hybridized. Due to Sp-hybridization, each carbon atom generates two Sp-hybrid orbitals. In this way there exists four Sp-orbital in
ethyne. These Sp-orbital    are arranged in linear geometry and 180o apart. Remaining py and pz unhybrid orbitals of each carbon atom lie perpendicular to the plane of Sp-orbitals.
 SIGMA BOND FORMATION:
One Sp-hybrid orbital of each carbon atom overlaps to produce one sigma bond between two
C-atoms.The remaining one Sp-orbital of each C-atom overlaps with one H-atom to produce sigma bond.
 Pi-BOND FORMATION:
Py and Pz orbital of two carbon atoms are un-hybrid and make parallel overlapping to produce pi-bond.
  BOND LENGTH:
The C–H bond is 1.09A and C-C is 1.2A.o.
BOND ANGLE:
HCC bond angle is 180o.

ethyne_orbital

 

ethyne2

METHODS OF PREPARATION
   BY THE HYDROLYSIS OF CALCIUM CARBIDE:
   CaC2 + 2H2O irreversible_arrow C2H2 + Ca(OH)2
 BY TETRA CHLOROETHANE:
 Cl2CH-CHCl2 + 2Zn irreversible_arrow C2H2 + 2ZnCl2
BY 1,2-DIBROMOETHANE:
Br-CH2-CH2-Br + KOH irreversible_arrow C2H2 + 2KBr + 2H2O
CHEMICAL PROPERTIES
   -COMBUSTION REACTION:
2C2H2 + 5O2 irreversible_arrow 4CO2 + 2H2O + heat
   -ADDITION REACTIONS:
   Addition of Hydrogen:
C2H2 irreversible_arrow CH2=CH2 irreversible_arrow C2H6
   Addition of Halogen:
C2H2 +Cl2 irreversible_arrow Cl-CH=CH-Cl irreversible_arrow Cl2CH-CHCl2
   Addition of Hydrogen Halide:
C2H2 + HBr irreversible_arrow CH2=CH-Br + HBr irreversible_arrow CH3-CHBr2
   Addition of HCN:
C2H2 + HCN irreversible_arrow CN-CH=CH-CN
   Addition of Water:
C2H2 + HOH irreversible_arrow CH2=CH-OH irreversible_arrow [rearrangement] irreversible_arrow CH3CHO (Ethanal)
   Oxidation of Ethyne:
   In cold solution
C2H2 + HOH + 3[O] irreversible_arrow 2HCOOH (Formic acid)
   In hot solution,
C2H2 +4[O] irreversible_arrow (COOH)2 (Oxalic acid)
   -SUBSTITUTION REACTIONS: 
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PHYSICAL PROPERTIES
  -Ethyne is a colourless gas with a characteristic smell.
-It has a melting point -81oC.
-It has a boiling point -84oC.
-It is significantly soluble in water. However, readily soluble in organic solvents.
USES OF ETHYNE
  -It is used in welding to produce oxy-acetylene flame of temperature about 3000oC.
-It is used in the synthesis of useful compounds such as ethanol, ethanoic acid, PVC, acetaldehyde.
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