What causes the ‘pop’ in soda pop?

Soda pop is a mixture of flavoured syrup, water and other ingredients. Carbon dioxide is also added under pressure. The mixture, still under pressure, is sealed in containers. Part of the carbon dioxide is trapped in the empty space at the top of the container. The rest of the gas dissolves in the liquid. Opening the container releases the pressure and the gas escapes. This makes the ‘pop’ sound.