Solubility of Gas in Liquid: Definition and Applications

Solubility of Gas in Liquid: When two or more two embryos develop from a single fertilized egg, then this phenomenon is known as Polyembryony. In the case of humans, it results in forming two identical twins. This phenomenon is found both in plants and animals. The best example of Polyembryony in the animal kingdom is the nine-banded armadillo. It is a medium-sized mammal found in certain parts of America and this wild species gives birth to identical quadruplets.

The production of two or more two embryos from a single seed or fertilized egg is termed as Polyembryony. In plants, this phenomenon is caused either due to the fertilization of one or more than one embryonic sac or due to the origination of embryos outside of the embryonic sac. This natural phenomenon was first discovered in the year 1719 by  Antonie van Leeuwenhoek in Citrus plant seeds.

Solubility of Gas in Liquid

Almost all gases are soluble in water, though to different extents. The existence of aquatic life in lakes, rivers, seas, etc., is due to the dissolution of oxygen gas in the water. Some gases are also soluble in solvents like ethyl alcohol, benzene, etc.

The solubility of any gas in a particular liquid is the volume of the gas in \({\rm{cc}}\) (converted to \({\rm{STP}}\)) that can dissolve in unit volume \(\left( {{\rm{1}}\,{\rm{cc}}} \right)\) of the liquid to form the saturated solution at the temperature of the experiment and under a pressure of \(1\) atmosphere.

This method of expressing the concentration is called the absorption coefficient of the gas and is usually represented by \({\rm{\alpha }}{\rm{.}}\)

Solubility of a gas in a liquid at a particular temperature is also expressed in terms of molarity (mole of the gas dissolved per litre of the solvent to form the saturated solution, i.e. in terms of \({\rm{mol}}{\mkern 1mu} {{\rm{L}}^{ – 1}}\)) or in terms of mole fraction \(\left( {{{\rm{X}}_{\rm{A}}}} \right)\) of the gas.

Factors Affecting Solubility of Gas in a Liquid

The important factors on which the solubility of a gas in a liquid depends are briefly explained below:

Nature of the Gas and the Solvent

Hydrogen, oxygen, nitrogen, and other gases dissolve just slightly in water, but carbon dioxide, hydrochloric acid, ammonia, and other gases are extremely soluble. Because of their reactivity with the solvent, the latter gases have a higher solubility.

Again oxygen, nitrogen, and carbon dioxide are much more soluble in ethyl alcohol than in water whereas, \({{\rm{H}}_{\rm{2}}}{\rm{S,}}\) and \({\rm{N}}{{\rm{H}}_{\rm{3}}}\) are more soluble in water than ethyl alcohol at the same temperature, and pressure. The greatest solubility of the gas in a solvent is again due to the chemical similarity between the gas and the solvent.

Effect of Temperature

The solubility of gases in liquids decreases with an increase in temperature. It is expected that some gas is usually expelled out of the solution on heating the gas solution. The same result also follows alternately as under:

The dissolution of a gas in a liquid is an exothermic process, i.e. it is accompanied by the evolution of heat. Thus,

\({\rm{Gas + solvent}} \leftrightarrow {\rm{solution + heat}}\)

Applying Le Chatelier’s principle, the increasing temperature would shift the equilibrium in the backward direction, i.e. and the solubility would decrease.

Though oxygen gas is more soluble than nitrogen gas at any temperature, the solubility of both the gases decreases with an increase in temperature, as represented in the figure.

Further, it may be pointed out that though generally the solubility of a gas in a liquid decrease with the increase of temperature, there are some exceptions. For example, the solubility of some sparingly soluble gases, such as hydrogen and inert gases, increases slightly with an increase in temperature, especially in the non-aqueous solvent such as hydrocarbons, alcohols and acetone.

Effect of Pressure

It is the most important factor influencing the solubility of a gas in a liquid at a particular temperature. A little thought reveals that as we compress the gas over the liquid (i.e., we increase the pressure), the solubility will increase. This may be explained as follows:

For the solution of a gas in a liquid, consider a system as shown in figure (a):

The lower part is the solution, and the upper part is gaseous at a pressure \({\rm{p,}}\) and temperature \({\rm{T}}{\rm{.}}\) Suppose a system is in dynamic equilibrium, i.e. rate of gaseous particles entering and leaving the solution as the same, which means that rate of dissolution \({\rm{ = }}\) rate of evaporation. Now, increase the pressure over the system, as shown in figure (b). The gas gets compressed to a smaller volume.

Hence, the number of gaseous particles per unit volume increases. As a result, the number of gaseous particles striking the solution’s surface and entering into it also increases until a new equilibrium is re-established. Thus, the solubility of gas in liquid increases with increasing the pressure above the solution.

A quantitative relation between pressure and solubility of a gas in a solvent was given by Henry \((1803).\) This relationship is known as Henry’s law.

Henry’s Law 

Henry’s law can be expressed as follows:

At constant temperature, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas. Thus, dolubility \({\rm{\alpha }}\) partial pressure of the gas.

Dalton, a contemporary of Henry, also found independently that the solubility of a gas in a liquid solution is a function of the partial pressure of the gas. If the solubility of a gas in a solvent is expressed in terms of the mole fraction of the gas in the solution, Henry’s law can also be expressed as follows:

The mole fraction of a gas in its solution in a solvent is directly proportional to the partial pressure of the gas over the solution.

Henry’s Law Equation

The most commonly used form of Henry’s law is as follows:

The partial pressure of the gas in the vapour phase is directly proportional to the mole fraction of the gas in the solution.

If \({\rm{x}}\) is the mole fraction of a gas in the solution and \({\rm{p}}\) is its partial pressure in the vapour phase, we have, according to Henry’s law,

\({\rm{P}}\,{\rm{ = }}\,{{\rm{K}}_{\rm{H}}}.{\rm{X}}\)

Where, \({{\rm{K}}_{\rm{H}}}\) is a constant known as Henry’s law constant. \({{\rm{K}}_{\rm{H}}}\) is a function of the nature of the gas because different gases possess different values of \({{\rm{K}}_{\rm{H}}}{\rm{.}}\) 

From the above equation, it is clear that given pressure, the solubility of a gas is inversely proportional to the wall value of \({{\rm{K}}_{\rm{H}}}{\rm{.}}\) At a given pressure, the higher the value of \({{\rm{K}}_{\rm{H}}}{\rm{,}}\) lower is the solubility of the gas. \({{\rm{K}}_{\rm{H}}}\) values for some common gases has given below.

From the above data, it is clear that the solubility of oxygen in water decreases with a temperature rise. This is why aquatic species are more comfortable in cold water than in warm waters.

Applications of Henry’s Law

Some of the important applications of Henry’s law are as follows.

1. Since the solubility of a gas in water increases with pressure, soft drink bottles are sealed under high pressure to accommodate more carbon dioxide in the soft drink.
2. If deep-sea divers (scuba divers) use air for respiration, they develop a medical condition known as bends which involve the blocking of capillaries. It is because air is mainly a mixture of oxygen and nitrogen. According to Henry’s law, the solubility of gases increases with an increase in pressure. When the diver breathes air under high pressure in the water, nitrogen dissolves in his blood. When the diver comes towards the surface, the pressure gradually decreases. It releases dissolved gases and leads to the formation of bubbles in the blood. It is quite painful and dangerous to live. To avoid bends and toxic effects of dissolved nitrogen in the blood, the tanks used by scuba divers are filled with air diluted with helium \(\left( {11.7\% \,{\rm{He}} + 56.2\% \,{{\rm{N}}_2} + 32.1\% \,{{\rm{O}}_2}} \right).\)
3. The pressure of oxygen in the air decreases in going up the mountains. At very high altitudes, the partial pressure of oxygen in the air is much less than that at the ground level. Therefore, people living at higher altitudes or climbers have low oxygen concentrations in the blood and tissues. It leads to weakness and loss of clarity of thinking. These symptoms create a condition known as anoxia.
4. Henry’s law explains the supply of inhaled oxygen to tissues. When air is inhaled, it combines with the haemoglobin of the blood in the lungs to form oxyhaemoglobin because, in the lungs, the partial pressure of oxygen is high. The partial pressure of oxygen is low in tissues. Hence, oxygen is released from oxyhaemoglobin and is utilised by the cells.

Limitations of Henry’s Law

Following are the limitations of Henry’s law.

1. Henry’s law applies to ideal gases only. However, the law can be applied to real gases at low pressure when the real gases approach the behaviour of ideal gases.
2.  This law does not apply to those gases which undergo a chemical change in the solution. For example, the law cannot be applied to ammonia which reacts with water to form \({\rm{N}}{{\rm{H}}_{\rm{4}}}{\rm{OH}}{\rm{.}}\)
3. The law cannot be applied to those gases which dissociate into ions in solution. For example, it cannot be applied to hydrogen chloride gas which dissociates into \({{\rm{H}}^ + }\) and \({\rm{C}}{{\rm{l}}^{\rm{ – }}}\) in solution.

Summary

Many gases dissolve in water. Oxygen dissolves only to a small extent in water. It is the dissolved oxygen that sustains all aquatic life. The solubility of gases increases with the increase of pressure. In this article, we have learned about the importance of solubility of gases in liquids, factors affecting the solubility of gases in liquids, Henry’s law, applications, and limitations of Henry’s law.

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FAQs on Solubility of Gas in Liquid

Let’s look at some of the commonly asked questions about the solubility of gases in liquids:

Q.1: What factors affect the solubility of a gas in a liquid?
A: The factors that affect the solubility of a gas in a liquid are the nature of the gas and solvent, temperature, and pressure.

Q.2: What is the effect of temperature on the solubility of a gas in liquid?
A: The solubility of a gas decreases with an increase in temperature. It is expected that some gas is usually expelled out of the solution on heating the gas solution. The same result also follows alternately as under:
The dissolution of a gas in a liquid is an exothermic process, i.e. it is accompanied by the evolution of heat. Thus,
\({\rm{Gas + solvent}} \leftrightarrow {\rm{solution + heat}}\)

Q.3: Can you dissolve gas into liquid?
A: Yes, a gas dissolves in liquids to form solutions. Henry’s law states that: “At constant temperature, the amount of gas that dissolves in a volume of liquid is proportional to the partial pressure of the gas in equilibrium with the liquid.”

Q.4: What type of solution is formed when gas is dissolved in liquid?
A: Homogeneous solution is formed when a gas is dissolved in liquid -for example, a mixture of carbon dioxide in water.

Q.5: What is an example of a gas-liquid solution?
A: Solutions having solute in a gaseous state and solvent in a liquid state are called gas-liquid solutions. Coca-Cola, a beverage, is an example of a gas-liquid solution, as it has carbon dioxide dissolved in water.

Q.6: What are the five examples of a solution?
A: The five examples of solutions are \(1.\) Sugar and milk, \(2.\) Ink in water \(3.\) Oxygen in water \(4.\) Salt in water \(5.\) Lemon juice in water.

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