From drinking a bottle of champagne for a celebration to open a soda while watching a good movie, everyone is familiar with fizz but… why do we hear a hissing sound when we open a soda?
As we all know, all carbonated beverages contain dissolved carbon dioxide (CO2) in the drink.
Carbon dioxide (CO2) is a nonpolar molecule formed of one carbon atom and two oxygen atoms, meaning that has low solubility in water
The solubility of any gas is directly proportional to the pressure applied on it. The carbonation process of soda involves pushing in CO2 through great pressure inside the water, reducing its volume, and pushing it into a small confined space.
To keep the soda carbonated, the pressure inside a soda is much higher than the pressure outside the soda bottle. Carbon dioxide prefers to be a gas, but inside a soda bottle where the pressure is high, it’s forced to be a liquid.
When the soda or a bottle of sparkling water is opened, there is suddenly a great pressure differential that needs to be equalised. As a result, the solubility of the carbon dioxide decreases, and the dissolved gas escapes as bubbles. This is the reason why we hear a hissing sound when we open a carbonated bottle.
Bubbles are pockets of carbon dioxide gas!
Once the the soda is opened, all of the gas will eventually escape from the liquid and the soda will go flat. Therefore, it is better to open the cap slowly to allow the gas to gradually expand and escape from the bottle, producing fizz.
What happens if you shake a soda?
When a soda or sparkling water is shaken, the extra gas at the top of the bottle is mixed with the liquid forming hundreds of microscopic bubbles. When the cap is taken off, the gas bubbles rapidly expand altogether while still in the liquid. As a consequence, the gas tries to escape the solution, pushing the liquid along with it and causing a non desirable spill.
What happens when you open a can of soda on the ocean floor?
The astronaut Chris Hadfiled did some experiments to test how life would be if we lived on the ocean floor.
This experiment included opening a can of soda when surrounded by 2 and a half atmospheres inside a submarine in the ocean floor. In addition, Chris vigorously shook the can before opening.
Surprisingly, when Chris opened the can of soda nothing happened. No bubbles, no messy spill. The pressure at the bottom of the sea is so high that no pressure is being released when the can is opened. The pressure inside the can is not as high as the pressure in the submarine.
Therefore, the solubility of the carbon dioxide is the same when the can is opened or when the can is closed.
Why do we use carbon dioxide and not gases as nitrogen in fizzy drinks?
There are two main reasons:
- While carbon dioxide is relatively soluble in water, other gases, such as nitrogen are more difficult to dissolve.
- When carbon dioxide dissolves, it reacts with water molecules to produce carbonic acid which is very important for the flavour and taste sensation.
However, beverages served “on nitro” are nothing new as nitro bubbles are finer than carbon dioxide bubbles and tend to reduce the perception of bitterness in beverages. Actually, Pepsi recently announced the launch of a nitrogen-infused version of its trademark soda called “Nitro Pepsi.”