Synthesis of silver acetylide

First, set up a gas generator to produce acetylene gas. Learn how to build one here.

Now lead some gas from the apparatus into a perfectly clean test tube that contains 10 ml of ammoniacal silver nitrate solution (w(AgNO3) = 1%). At first a white precipitate forms, which soon turns gray. We can also see the formation of a silver mirror on the glass wall.

The solid is filtered off. We make sure that not too much substance gets into a filter bag. We also rinse the substance, so that it collects in the middle of the filter bag. Do not tear the filter apart. Fold it into a nice little packet. Attach warning label: Careful, explosive, silver acetylide.

Important: After filtering, residues in the glass are treated with half-concentrated hydrochloric acid. This destroys residues of the silver acetylide.

What happened?

Acetylene is an acid, just a very weak one. This can already be seen in the formation reaction of ethine from calcium carbide and water! This reaction is based on the fact, that calcium carbide is the salt of a weak acid (ethine). At the same time, ethine is very volatile (gas) and water a stronger acid. This means, the water molecule reacts with the calcium carbide to form ethine. This protolysis reaction then also leads to the alkaline reaction of the solution.