Question

A gaseous alkyne is burned completely in oxygen. The volume of the water vapour that forms equals the volume of the alkyne burned (the volumes are measured at the same temperature and pressure). Name the alkyne and write a balanced equation for its combustion.

Short answer

Acetylene ${\text{C}}_{\text{2}}{\text{H}}_{\text{2}}$is an alkyne that when burned in oxygen. The balanced equation for this combustion is role="math" localid="1668147550977" ${\text{C}}_{\text{2}}{\text{H}}_{\text{2}}\text{+}\frac{\text{5}}{\text{2}}{\text{O}}_{\text{2}}\to {\text{2CO}}_{\text{2}}{\text{+H}}_{\text{2}}\text{O}$.

Step-by-step solution

Water vapour.

Acetylene${\text{C}}_{\text{2}}{\text{H}}_{\text{2}}$ is an alkyne that forms carbon dioxide and water vapour when burned in oxygen. The volume of water vapour is equal to its initial volume.

The equation for this reaction is

${\text{C}}_{\text{2}}{\text{H}}_{\text{2}}\text{+}\frac{\text{5}}{\text{2}}{\text{O}}_{\text{2}}\to {\text{2CO}}_{\text{2}}{\text{+H}}_{\text{2}}\text{O}$.

Balanced equation

One mole of acetylene yields one mole of water.

The balanced reaction can also be written as :

${\text{2C}}_{\text{2}}{\text{H}}_{\text{2}}{\text{+5O}}_{\text{2}}\to {\text{4CO}}_{\text{2}}{\text{+2H}}_{\text{2}}\text{O}$.

Therefore, the alkyne is acetylene.