Question

Explain why pressure substantially affects the solubility of \(\mathrm{O}_{2}\) in water but has little effect on the solubility of \(\mathrm{NaCl}\) in water.

Short answer

In summary, pressure substantially affects the solubility of \(O_2\) in water because it's a gas, and according to Henry's Law, gas solubility is directly proportional to the applied pressure. On the other hand, the solubility of ionic compounds like \(NaCl\) is mainly influenced by temperature and solvent nature rather than pressure, as described by Le Chatelier's Principle. Therefore, pressure has little effect on the solubility of \(NaCl\) in water.

Step-by-step solution

Understanding solubility

Solubility is the maximum amount of a solute that can dissolve in a solvent at a given temperature and pressure. In this case, the solutes are oxygen and sodium chloride, while the solvent is water.

Effect of pressure on gas solubility

According to Henry's Law, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid. When the pressure increases, more gas molecules are forced into the liquid, increasing its solubility. This is why the solubility of oxygen, a gas, in water is significantly affected by pressure. For example, when pressurizing a can of soda, the increased pressure forces more carbon dioxide gas to dissolve in the liquid, which gives the soda its characteristic fizz when opened, and the pressure is released.

Effect of pressure on solubility of ionic compounds

When it comes to ionic compounds, such as sodium chloride (NaCl), Le Chatelier's Principle provides insight into the effect of pressure on solubility. Le Chatelier's Principle states that if a stress or change is applied to a system in equilibrium, the system will adjust to counteract the applied stress or change. However, NaCl is an ionic compound, and the dissolution process involves breaking and forming ionic bonds. The solubility of ionic compounds is mainly affected by temperature and the nature of the solvent, while the pressure has minimal influence on solubility.

Dissolution of NaCl in water

When NaCl dissolves in water, the ionic bonds between its Na⁺ and Cl⁻ ions are broken, and new hydration shell bonds are formed between the ions and the water molecules. This process is relatively undisturbed by changing pressures because the reaction is not significantly pressure-dependent.

Comparing the effect of pressure on O₂ and NaCl solubility

Based on our understanding of solubility, the effect of pressure on solubility is significantly more pronounced in the case of gases like oxygen, as described by Henry's Law, than it is for ionic compounds like sodium chloride, as described by Le Chatelier's Principle. In conclusion, pressure substantially affects the solubility of O₂ in water due to its direct proportionality with gas solubility, as described by Henry's Law. In contrast, pressure has little effect on the solubility of NaCl in water, as ionic solubility is mainly influenced by temperature and solvent nature rather than pressure.

Key concepts

Henry's Law

Henry's Law is a fundamental principle that describes how gases dissolve in liquids. According to this law, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above that liquid. This means that if you increase the pressure over the liquid, more gas molecules are "pushed" into the liquid, increasing the gas's solubility.
For example, when you open a bottle of soda, you can hear a hiss. That's the sound of gas escaping as the pressure over the liquid is released. Before opening, the pressurized carbon dioxide gas is dissolved abundantly, making the soda fizzy. Henry's Law is an excellent explanation for why oxygen dissolves more in water when pressure increases.

Le Chatelier's Principle

Le Chatelier's Principle provides insight into how systems adjust to changes in conditions like pressure, temperature, and concentration to maintain equilibrium. For solutes like ionic compounds, this principle helps us understand why solubility changes occur under various conditions.
However, when it comes to the solubility of ionic compounds such as sodium chloride (NaCl), this principle shows that pressure changes do not significantly alter solubility. The reason is that the process of dissolving ionic compounds does not involve gas volume changes, so pressure has little effect. Instead, temperature plays a more crucial role.

Gas Solubility

The concept of gas solubility is mainly governed by Henry's Law. As pressure increases, the solubility of a gas like oxygen in water significantly rises. This property is vital in various real-life applications, ranging from carbonated beverages to the physiological processes in divers.
However, once normalized or the pressure is decreased, the gas can quickly come out of the solution, which is why bubbles form when you pour a soda or open a highly pressurized container. Thus, understanding gas solubility is crucial for predicting and manipulating how gases behave in different environments.

Ionic Compounds

Ionic compounds, such as sodium chloride, behave differently when it comes to solubility in water compared to gases. The solubility of these compounds primarily depends on temperature and the solvent's nature rather than pressure.
When NaCl dissolves, its ions separate and become surrounded by water molecules, forming a solution. The energy involved in dissolving and forming new bonds doesn't change significantly with pressure, making the solubility fairly consistent regardless of external pressure changes.

• The stability of ionic bonds requires significant energy to be overcome.
• Dissolution involves hydration and separation of ions, not influenced much by pressure.

Solvent Effects on Solubility

The type of solvent can significantly affect solubility. Water, a polar solvent, is excellent at dissolving ionic and polar compounds due to its ability to create hydrogen bonds.
For gases, the solvent's characteristics have less to do with its capacity to dissolve them compared to pressure and temperature. But for substances like NaCl, the polarity and capacity of hydrogen bonding in water play a significant role.
In summary, while pressure dramatically influences gas solubility in water, as shown in Henry's Law, the solubility of ionic compounds depends more on temperature and the nature of the solvent, as demonstrated by how NaCl dissolves in water.