Introduction:

Henry's law states that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid. However, carbon dioxide (CO2) exhibits a significant deviation from Henry's law when dissolved in water. This deviation can be explained by several factors.

Key Factors Affecting CO2 Solubility:

1. Ionic Interactions:
When CO2 dissolves in water, it reacts with water molecules to form carbonic acid (H2CO3), which can further dissociate into bicarbonate ions (HCO3-) and hydrogen ions (H+). These ionic interactions contribute to the deviation from Henry's law.

2. pH and Ionization:
The ionization of carbonic acid and the subsequent formation of bicarbonate ions depend on the pH of the water. At higher pH values, bicarbonate ions dominate, while at lower pH values, the concentration of carbonic acid increases. This pH dependence affects the solubility of CO2 in water and deviates from the linear relationship predicted by Henry's law.

3. Complexation and Hydrogen Bonding:
CO2 can form complexes with various compounds present in water, such as metal ions, organic molecules, and proteins. These complexation processes can influence the solubility of CO2 and cause deviations from Henry's law.

4. Temperature Dependence:
The solubility of CO2 in water is also influenced by temperature. As temperature increases, the solubility of CO2 decreases. This temperature dependence is not accounted for in Henry's law and contributes to the deviation.

5. Pressure Dependence:
Unlike other gases that follow Henry's law, the solubility of CO2 in water is not solely dependent on pressure. CO2 can undergo chemical reactions and ionization, as mentioned earlier, which affect its solubility and result in a deviation from Henry's law.

Conclusion:

In conclusion, the deviation of CO2 from Henry's law in water can be attributed to several factors, including ionic interactions, pH and ionization, complexation and hydrogen bonding, temperature dependence, and pressure dependence. These factors play a crucial role in determining the solubility of CO2 in water and explain why it significantly deviates from the linear relationship predicted by Henry's law.