# Reduction of copper oxide by hydrogen in the lab

Why does the hydrogen which is passing continuously through the tube have to be burnt when it is passing out from the tube? Why can it not be allowed to just escape simply?

Burning the hydrogen gas at the exit stream of the copper oxide reduction tube is simply one way to assure that it does not accumulate to explosive levels in the lab. Although hydrogen gas is not toxic, it is flammable in air at concentrations as low as $\pu{4\%}$. As the combustion product of hydrogen and oxygen is mainly water vapor, this technique makes for a simple, safe means for disposing of the excess hydrogen from the copper oxide reduction process.