Sparkling water, a beverage enjoyed worldwide, is a simple example of a chemical solution. The effervescence that gives the drink its fizz is the result of combining two substances to create a uniform mixture. Understanding the composition of this everyday drink provides insight into how different states of matter interact at a molecular level.
Understanding Solutes and Solvents
A solution is a homogeneous mixture where one substance is completely dispersed into another. Solutions are defined by two primary components: the solvent and the solute. The solvent is the substance that does the dissolving and is almost always the component present in the greatest quantity. The solute is the substance being dissolved by the solvent and is typically the minor component. Solutes can exist in any physical state—solid, liquid, or gas—before they are dissolved.
Identifying the Components of Sparkling Water
In sparkling water, the solvent is the water, as it makes up the vast majority of the beverage’s volume. Carbon dioxide (CO2), the substance being dissolved to create the bubbles, functions as the solute. Although CO2 is a gas, it is the minor component incorporated into the liquid water, fitting the definition of a solute.
The process of dissolving gaseous CO2 into the liquid water is called carbonation, which results in a mild chemical reaction. A small portion of the dissolved CO2 reacts with water molecules (H2O) to form carbonic acid (H2CO3). This weak acid provides the slightly sharp or “tangy” flavor associated with carbonated drinks.
The Physics of Dissolving Gas in Liquid
To create sparkling water, carbon dioxide gas is injected into the water under high pressure. This high pressure is the primary mechanism used to force gas molecules into the liquid, increasing the amount of CO2 the water can hold. The solubility of a gas is directly related to the pressure above the liquid; higher pressure results in more gas dissolving.
Temperature also plays a significant role in maintaining the dissolved gas. Unlike solids, the solubility of gases in a liquid decreases as the temperature increases. Chilling the water allows it to hold a greater concentration of the CO2 solute because cold temperatures help keep the gas molecules “trapped” by lowering their kinetic energy.
When a sealed bottle is opened, the high pressure holding the gas is instantly released to atmospheric pressure. This sudden drop causes the water to become supersaturated, meaning it holds more dissolved gas than is stable under the new conditions. Consequently, the excess carbon dioxide rapidly escapes from the solution and forms the visible bubbles that rise to the surface. These bubbles form most easily at nucleation sites, which are tiny imperfections or particles on the inside of the glass or bottle.