Acetylene from Calcium carbide

Almost the entire organic chemistry of the GDR was based on acetylene. However, after the fall of the Wall, they really only cared about petrochemistry. Acetylene chemistry was disposed with many others.

Acetylene, or better ethyne, is still a fascinating substance. So today we want to experiment a little with it.

It is made by bringing calcium carbide into contact with water. Instead of water, some also like to use sodium chloride solution, as the gas is less soluble in it.

Regarding the commercial form of calcium carbide, it should be said that it is generally sold with a finely powdered silicate drying agent. Of course, you shouldn’t take that, but rather the stone-like carbide lumps hidden in it ..

Experiment 1: Production of ethyne

In a gas evolution apparatus, water is carefully added to calcium carbide (F) from a dropping funnel. The amount of water is regulated according to gas formation. Do not add too much water at once, as the system can heat up so much that it ignites itself.

We collect the gas in four numbered glass cylinders and close them with flat-ground glass lids.

The equation of the exothermic formation reaction is:

This does not apply to all carbides; aluminum carbide Al4C3 reacts to form methane. This is due to the fact that the crystal lattice of calcium carbide already contains C22- ions from the start, while individual C4 islands can be found in the lattice of aluminum carbide.

By the way, pure acetylene smells a aromatic and sweet. The typical “carbide smell”, on the other hand, comes from phosphines. Phosphines are phosphorous-hydrogen compounds such as PH3. These are also the reason for the possible self-ignition of the gas during its production. (They are known as flames in the swamp gas, which contributed to the legend of the bog spirits.) Phosphines come from the reaction of water with calcium phosphide. The latter, in turn, is produced by reduction from phosphate, which is contained as an impurity in the raw materials for carbide production, lime and coal.

Burning test with acetylene

Under no circumstances should you take the first cylinder, as it can contain oxyhydrogen acetylene!

We light a stick, open the lid of the glass cylinder and ignite it.

This sample does not exactly show that ethine burns with a hot flame. You can show that with acetylene oxyhydrogen. The ethine/oxygen mixture exceeds that of the hydrogen/oxygen by far … Our experiment shows, however, why ethine was also burned specifically for soot extraction, among other things. Because the soot development is amazing.