What causes acetylene to explode

26.037 g / mol
 
not specified
1.1772 g / l (gas, 0 ° C, 1013 hPa)
(Acetylene to air = 0.91)
−81.5 ° C
−84.7 ° C
Conc. At 20 ° C 1.185 g / l
2.5 to 100% by volume (air)
+305 ° C



Colorless gas


Special notes for the school
Gas cylinders containing acetylene are not recommended for chemistry classes in schools. To demonstrate the properties, the gas can be produced from calcium carbide. Due to its high explosion limit, acetylene forms explosive mixtures with air relatively easily. Work is always carried out with good ventilation. During demonstrations of flammability, the gas is immediately flared. It is essential to wear protective goggles.
properties
Effect on the human body

Acetylene is not toxic in low concentrations. Toxic effects are only to be expected from 20 percent by volume in the breath, from 35% it has a narcotic effect.

Chemical-physical properties

Pure acetylene is odorless. It is sold in bottles with a red-brown shoulder. Acetylene is only sparingly soluble in water, but it dissolves well in acetone, ethanol, benzene and chloroform.



Acetylene is sold in bottles with a red-brown shoulder.
(Photo courtesy of Gebrüder Gloor AG)

The gas, which is technically obtained from calcium carbide, has an unpleasant smell because it is contaminated with hydrogen sulfide, ammonia, hydrogen phosphide and organic sulfur and phosphorus compounds. It burns in the air with a strongly sooting and glowing flame that can reach temperatures of up to 1900 ° C.



Carbide reacts with water.

Movie available on DVD

With pure oxygen, the flame can even heat up to over 3000 ° C. Acetylene-air mixtures are highly explosive. Pure acetylene can detonate under pressure. It must not come into contact with copper or silver pipes, as highly explosive and very touch-sensitive copper or silver acetylide is formed. The formation of acetylides also takes place when acetylene is introduced into aqueous solutions of silver or copper (I) salts. This reaction also serves to detect acetylene. Due to the presence of a triple bond and the unsaturated character of acetylene, it shows a large number of addition reactions.

1st example 
Halogens can be added, whereby haloalkanes are formed in two steps:

1st step: ethyne + chlorine Dichloroethene
2nd step: dichloroethene + chlorine Tetrachloroethane

Tetrachloroethane is poisonous, so calcium hydroxide splits off hydrogen chloride and trichloroethene is obtained, which is used as a solvent for fats, oils, resins and paints.

2nd example  
With the help of a catalyst such as mercury (II) sulfate in sulfuric acid, it is possible to attach water to the ethyne molecule. In an intermediate step, unstable vinyl alcohol is produced, which further reacts to form ethanal:

1st step: C2H2 + H2O H2C = CH-OH (vinyl alcohol)
2nd step: H2C = CH-OH H3C-COH (ethanal)

A large number of organic compounds can be synthesized from ethyne by addition reactions. These include, for example, acrylic acid, acrylonitrile, vinyl chloride or vinyl ether.
Manufacturing
use
Acetylene is used as a fuel gas in welding. Acetylene is sold in yellow gas cylinders. These are filled with a porous mass such as pumice stone or kieselguhr and contain acetone, which prevents explosive self-decomposition under high pressure. Along with ethylene, acetylene is one of the most important starting materials for the production of organic compounds. In the past, it was occasionally used as an anesthetic in medicine.



In oxy-fuel welding, a fuel gas is mixed with oxygen in a welding torch in such a way that
that a flame is created that melts the iron but does not oxidize it.

Movie available on DVD


Further information and media
Hydrocarbons as a group of substances in organic chemistry
Oxy-fuel welding