I did a double-take when I first read the experiment guide for one of my recent organic chemistry labs. “We get to blow something up?” I thought there had to be a mistake, there’s no way they would trust some college students with an explosive material. But there was no mistake, the objective of the experiment was to produce silver acetylide (Ag2C2) which is a greyish solid. Silver acetylide is shock and heat sensitive, which means it will detonate with an increase in temperature or any type of shock. When it is dry, the solid will explode given the slightest shock. This lab experience was both exciting and nerve-racking.
The explosive nature of the compound is derived from acetylene, whose structure is two carbons bonded with a triple bond. Acetylene is a clear gas that is odorless, poisonous, and flammable. We had no vessel to hold the gas after producing it, so it immediately had to be used to synthesize a solid, Ag2C2. To produce acetylene, distilled water was added to calcium carbide (CaC2). Calcium carbide is a greyish/white solid that looks like small pebbles. Due to its dangerous properties, the acetylene was directly transferred to another solution after it was produced. Silver acetylide (Ag2C2) forms with the reaction of acetylene and silver nitrate (AgNO3). The acetylene was funneled from the initial reaction into the bottom of a graduated cylinder which held silver nitrate. This allowed the acetylene (a gas) to bubble through the silver nitrate liquid solution and solid silver acetylide formed.
After all of the water and calcium carbide reacted and bubbles ceased eluting through the silver nitrate, the solid had to be filtered off. We used vacuum filtration to isolate the solid silver acetylide, but made sure to keep the solid slightly hydrated. As I indicated earlier, if the silver acetylide became too dry, it would detonate with movement (shock). The silver acetylide was placed in a foil holder and was then placed on a heat source. We stepped back and closed the hood to allow the solid to explode. The intended explosion was one pop, but mine ended having an initial pop and then a series of tiny pops, like a machine gun, several minutes later. We then had to be very careful cleaning up. There was the occasional “snap” on our table where tiny pieces of the solid ended up. To negate the substance’s tendency to explode, the solid could be put in water. Therefore, we cleaned the lab table with very wet paper towels and soaked all equipment in water and then cleaned everything very thoroughly. Overall, the lab was very exciting and I learned a lot about the physical properties of acetylene. Interestingly, acetylene will produce an explosive solid when reacted with other metals, not just silver.
One interesting fact about the explosion of the solid is that only solid products are formed when it detonates. In nearly all explosions, gas is released at detonation, but solid carbon and solid silver are the only products when silver acetylide explodes. Apart from the excitement of the explosive lab, I learned about safety and always being careful in a lab setting. It is very important to be aware of ones surroundings and focus when chemicals are present. If you mix the wrong chemicals, it can produce something poisonous or explosive, like in our lab. This lab was effective at demonstrating how to treat chemicals in a lab and handle them with care. Not to mention, we got to blow something up.