Atmospheric Gas Solubility in Water Explained

The solubility of a gas in a liquid refers to the maximum amount of that gas that can dissolve in a given amount of the liquid at specific temperature and pressure conditions. Standard Temperature and Pressure (STP) conditions are typically defined as a temperature of 273.15 K (0°C) and a pressure of 100 kPa (1 atm). Understanding how atmospheric gases interact with water is crucial in many scientific fields.

Solubility of Common Atmospheric Gases in Water

Let's examine the solubility of the gases mentioned in the options at STP:

• Oxygen ($O_2$): Oxygen is essential for aquatic life, but its solubility in water is relatively low. It is considered sparingly soluble. At standard conditions (0°C and 1 atm), about 70 mg of oxygen can dissolve in 1 liter of water.
• Carbon Dioxide ($CO_2$): Carbon dioxide is significantly more soluble in water than oxygen. It readily dissolves and reacts with water to form carbonic acid ($H_2CO_3$), which affects water's pH. Its solubility is much higher compared to oxygen and nitrogen.
• Nitrogen ($N_2$): Nitrogen constitutes the largest portion of Earth's atmosphere (~78%). However, it is known for its very low solubility in water. While it does dissolve slightly, its insolubility is a key characteristic, especially compared to gases like oxygen or carbon dioxide. At 0°C and 1 atm, approximately 25 mg of nitrogen dissolves in 1 liter of water.
• Chlorine ($Cl_2$): Chlorine gas is soluble in water, although it also reacts to form hydrochloric acid (HCl) and hypochlorous acid (HOCl). Its solubility is higher than that of nitrogen and oxygen.

Comparing Gas Dissolution in Water

Comparing the solubilities:

• Carbon dioxide ($CO_2$) is highly soluble.
• Chlorine ($Cl_2$) is soluble.
• Oxygen ($O_2$) is sparingly soluble.
• Nitrogen ($N_2$) exhibits the lowest solubility among these common atmospheric gases.

Therefore, at standard temperature and pressure conditions, Nitrogen is the atmospheric gas listed that dissolves the least in water, often being considered practically insoluble in many contexts compared to the others.