Gas Solubility in Water: Which Gas is Most Soluble in Water?

Solubility of Gases in Water

The solubility of gases in water is of great importance for environmental science, biology, and engineering. The ability of a gas to dissolve in water can play a key role in the strength of molecular interactions, solvation, chemical behavior of a substance, and transport of this substance in a solvent. 

The term 'solubility' in reference to gases in water is simply the concentration of a gas that is physically dissolved in a liter of water.

It is important to note that once a gas has dissolved in water, the solute system will favor mixing and contain some solute in the gaseous form. In this light, it appears that the solubility of gases in water must decrease as solute is being created; however, this is unable to occur in an exact way because gases are uniquely different from solids and liquids: both of the latter forms of matter are incompressible at a fixed volume, and so there are molecular obstacles to intermingle and form solutions. 

Alternatively, gases are highly compressible, which greatly minimizes such intermolecular obstacles. The solubility of a gas in water is dependent on the temperature of that water, the pressure of the gas considered, and the selection of a pair of compounds to be in contact. 

In addition, the strength of the forces that a gas in solution experiences in comparison to when it is in the gaseous stage is in a ratio of approximately twenty to one. This strength is characteristic of acid-base interactions. The study of the solubility of a gas in water transpired in 1803; however, the pursuit of knowledge in this particular field was made famous before this date in 1774. A collection of data on gas solubility in water has since been documented, including inputs from highly comprehensive data tables.

1. Factors Affecting Gas Solubility in Water

The solubility of gases in water is influenced by different variables. Among these, temperature plays a major role due to its direct impact on the kinetic energy of particles. As a rule of thumb, the solubility of a gas in water decreases with increasing temperature. 

Pressure is another factor that could affect the solubility of a gas. Generally, the higher the pressure, the greater the solubility of a gas in a liquid. The relationship between solubility and pressure is often described as S = k × P, where S is the solubility constant, P is the partial pressure of the gas, and k is a constant. Thus, each gas has its own constant depending mostly on its solubility in the liquid in question.

As a further note, the solubility of a gas in water is also influenced by the similarity of the gas with the solvent. Thus, polar gases are likely to dissolve in polar solvents, and nonpolar gases are likely to dissolve in nonpolar solvents according to the 'like dissolves like' rule. 

Other factors, such as partial pressures of other gases, the nature of solutes, and atmospheric conditions such as altitude, could also play a minor role in the solubility of a gas in water. Given the importance of alignment in properties between gas and water in relation to the level of solubility, several other factors interact to further complicate the solubility of a gas in water. 

Salts from solids and other ions originating within the water can also inhibit or facilitate the solubility of a gas.

2. Properties of Gases Highly Soluble in Water

Most gases in the atmosphere are mixtures of several molecules such as nitrogen, oxygen, carbon dioxide, and small concentrations of other gases and constituents. The solubility of any of these gases in water is directly proportional to its partial pressure in the atmosphere. 

The water solubility of gases is related to temperature and the physical properties of the gases that dissolve. We will look at some properties that can be useful in predicting the solubility of gases. Included are properties whose values may be estimated by calculating the dependence of solubilities, the heat of the solution, the limiting slope, and both the high and low-temperature behavior of the solubility. 

Consistency in available data allows for the approximation of the temperature coefficient of the heat of the solution of gases in water. The plot of the dependence of solubility on temperature can be usefully divided into three parts, beginning if the heat of the solution is a slowly varying function of temperature. 

Several simple examples qualitatively illustrate these properties, such as the limitation from above of the solubility of nitrous oxide in water and the shape of the solubility curve.

3. Applications and Significance of Gas Solubility in Water

Gas solubility in liquids facilitates the various processes essential for life and industry on Earth. In natural bodies of water, the availability of dissolved gases significantly impacts the health of ecosystems, as does the treatment of waste. 

In physiology and medicine, one must understand how different concentrations of different gases can be maintained in the blood. Carbonated beverages contain dissolved carbon dioxide at pressures higher than atmospheric pressures; soda in cans does not taste flat despite its high concentration of carbon dioxide because the can is pressurized. 

Coke in cans that are accidentally punctured will release pressure, lose dissolved carbon dioxide, and taste flat. It is important to consider the chemistry of solubility for these many different applications.

Gases required by the body and used by industry dissolve readily in water. The air is a mixture of gases, most of which are present. When you breathe in air, the oxygen first dissolves in the moist film lining of your alveoli before it crosses into your bloodstream. 

The concentration of gases in the liquid portion of the blood is much lower than that in the gaseous phase in the red blood cells. Aquatic animals can only survive in water with sufficient oxygen content. If aquatic animal water supplies have been tampered with, excessive carbon dioxide will kill the fish. 

These species of fish are mouth breathers; that is, they absorb oxygen from the air and not from the gills present in the water. To avoid suffocating, fish need to have an environmental gill surface area at least equal to their body surface area. 

Along with heat and sweat, the human body releases about 350 mL of carbon dioxide per day; if this waste were not removed, we would die. Water purification of municipal wastewater and pharmaceutical manufacturers addresses water removal.

Gas Solubility:

Boundless Learning: https://courses.lumenlearning.com/boundless-chemistry/chapter/solubility/

Carbon Dioxide: https://www.epa.gov/climate-indicators/climate-change-indicators-ocean-acidity