Why does shaken soda explode

Soda water, also called carbonated water, is plain water in which carbon dioxide is dissolved. The process of dissolving carbon dioxide in water is called carbonation. This process results in the formation of carbonic acid. In addition to carbon dioxide, a small amount of sodium chloride, sodium citrate, sodium carbonate, potassium citrate, potassium carbonate, potassium sulfate and disodium phosphate are also added. These additives impart a distinct taste to the soda water and make it more delectable. Carbonated water is extensively used as a diluent for alcoholic drinks, like whisky and brandy.

Often, when soda water can is vigorously shaken, and opened, it explodes. However, explosion doesn’t occur when the can is opened as such, that is, without shaking. During the carbonation process, water and carbon dioxide form a solution. The mixture is poured in the container and sealed. Before sealing the can, carbon dioxide gas is filled in the empty space at the top of the can. When the can is normally opened, the hissing sound is heard. This sound denotes that carbon dioxide gas collected at the top of the container is escaping. Once, the collected carbon dioxide gas is released, the dissolved gas begins to escape which results in the familiar effervescence.
When the soda water can is rigorously shaken, that liquid-gas solubility equilibrium is disturbed. Furthermore, because of shaking, small bubbles are created in the liquid that collect at the headspace of the container. These bubbles act as nucleation sites on which carbon dioxide start collecting. Thus, when shaken, carbon dioxide moves from the soluble state to gaseous state, and starts accumulating at the headspace of the container. Under such conditions, if the soda water can is opened, explosion is bound to occur because all the carbon dioxide gas will try to escape from the small opening, and in a bid to do so, it will also carry away the ingredients of the can.
On the contrary, if the can is not opened immediately after shaking it energetically, the gas-liquid solubility equilibrium is again regained and no explosion occurs.

The best way to prevent explosion is to open the can very slowly so that the change in the pressure is not drastic and sudden. Another trick is to gently tap the sides, top and bottom of the can for a few seconds. This will bring the bubbles to the top of the ingredients and prevent them from escaping quickly. It has been observed that soda water can with wider openings are less likely to explode because they provide more space for carbon dioxide to escape.