The weak electrolyte \(\mathrm{NH}_{3}(g)\) does not obey Henry's law. Why? \(\mathrm{O}_{2}(g)\) obeys Henry's law in water but not in blood (an aqueous solution). Why?

Henry's law states that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas on the surface of the liquid, under constant temperature. Mathematically, it can be expressed as: \[C = k_H \times P\] Where: - \(C\) is the concentration of the dissolved gas in the liquid - \(k_H\) is Henry's law constant (depends on the specific gas being dissolved and the temperature) - \(P\) is the partial pressure of the gas above the liquid It is important to note that Henry's law only applies to dilute solutions and to gases that do not undergo any chemical reaction with the solvent.

Ammonia (NH3) does not obey Henry's law because it forms a weak electrolyte when it dissolves in water. When ammonia dissolves in water, it can react with water molecules to form ammonium ions (\(\mathrm{NH}_{4}^+\)) and hydroxide ions (\(\mathrm{OH}^-\)), as shown in the following reaction: \[\mathrm{NH}_{3}(aq) + \mathrm{H}_{2}\mathrm{O}(l) \rightleftharpoons \mathrm{NH}_{4}^+(aq) + \mathrm{OH}^-(aq)\] This reaction is reversible, and the equilibrium shifts depending on the concentration of ammonia and other ions in the solution. Because ammonia undergoes a chemical reaction with water, it does not follow Henry's law.

In water, oxygen (O2) follows Henry's law because it is only physically dissolved and does not undergo any chemical reaction with water molecules. Thus, the solubility of oxygen in water is directly proportional to the partial pressure of oxygen above the water. However, in blood (which is an aqueous solution), the behavior of oxygen is different. In blood, the majority of oxygen is transported by binding to a protein called hemoglobin within red blood cells. This binding process is not described by Henry's law and is influenced by factors like pH, temperature, and the partial pressure of carbon dioxide. A relatively small amount of oxygen remains physically dissolved in blood plasma, following Henry's law. In conclusion, ammonia (NH3) does not obey Henry's law because it undergoes a chemical reaction with water, while oxygen (O2) obeys Henry's law in water due to physical dissolution but does not follow it in blood due to its binding to hemoglobin.