Synthesis database: Calcium oxide

Calcium oxide can be simply synthesized by using calcium hydroxide. Calcium oxide can also be easily found and bought in form of quicklime, but the problem is that quicklime is mostly packed in bags through which, after longer periods of time, moisture can get in and slowly convert the oxide to the hydroxide (slaked lime).

This reaction is reversible ( CaO + H₂O <-> Ca(OH)₂ ), and this experiment is based on the mentioned reaction. One needs to prepare a thin metal plate, calcium hydroxide, and a heat source capable of generating temperatures above 500 °C. It is best to use some type of gas burner.

On the metal plate, one should spread the calcium hydroxide in a thin layer, taking care that it is not spread over a too large surface. After that, the burner is ignited. Mostly, it is enough to heat the Ca(OH)₂ from 45 to 60 minutes, but depending on the quantity, it can sometimes take a bit longer.

During the reaction, nothing spectacular happens, since water is slowly released from the mixture of CaO and Ca(OH)₂, in which the amount of the oxide slowly increases, while the amount of hydroxide slowly decreases. After the reaction is finished, the gas burner can be turned off, and the obtained calcium oxide is transferred to a container that can be tightly closed in order to avoid contact with moisture.

The success of the reaction can simply be determined with the help of stoichiometry - the mass after the reaction must be lower than the mass before the reaction, since the molar mass of calcium oxide is lower than the molar mass of calcium hydroxide. Additionally, one can add a small amount of the obtained calcium oxide to a small amount of water. This reaction produces the compound we started with - calcium hydroxide, thereby heating the solution. The increase in temperature can be measured with a thermometer, or even felt by touching the container in which the reaction is carried out.