CHEMISTRY OF ETHYNE
| Molecular formula = C2H2
Empirical formula = CH
Molecular mass = 26
Empirical mass = 13
Common name = Acetylene
Homologous series = Alkynes
| 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.
Py and Pz orbital of two carbon atoms are un-hybrid and make parallel overlapping to produce pi-bond.
The C–H bond is 1.09A and C-C is 1.2A.o.
HCC bond angle is 180o.
METHODS OF PREPARATION
| BY THE HYDROLYSIS OF CALCIUM CARBIDE:
CaC2 + 2H2O C2H2 + Ca(OH)2
BY TETRA CHLOROETHANE:
Cl2CH-CHCl2 + 2Zn C2H2 + 2ZnCl2
Br-CH2-CH2-Br + KOH C2H2 + 2KBr + 2H2O
| COMBUSTION REACTION:
2C2H2 + 5O2 4CO2 + 2H2O + heat
Addition of Hydrogen:
C2H2 CH2=CH2 C2H6
Addition of Halogen:
C2H2 +Cl2 Cl-CH=CH-Cl Cl2CH-CHCl2
Addition of Hydrogen Halide:
C2H2 + HBr CH2=CH-Br + HBr CH3-CHBr2
Addition of HCN:
C2H2 + HCN CN-CH=CH-CN
Addition of Water:
C2H2 + HOH CH2=CH-OH [rearrangement] CH3CHO (Ethanal)
Oxidation of Ethyne:
In cold solution
C2H2 + HOH + 3[O] 2HCOOH (Formic acid)
In hot solution,
C2H2 +4[O] (COOH)2 (Oxalic acid)
CONSULT YOUR TEXT BOOK
| 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.