Problem 2 - Advanced Problems in Physical Chemistry for Competitive Examinations

Question

Which of the following statement is correct regarding the solubility of gas in water? (a) Solubility increases with the increase in temperature. (b) A more polar gas will be less soluble. (c) Solubility increases with the increase in pressure. (d) Solubility is always endothermic process.

Step-by-Step Solution

Answer

The correct statement regarding the solubility of gas in water is (c) Solubility increases with the increase in pressure.

Step 1: Understanding Solubility Principles

Recognize that the solubility of gases in liquids is governed by principles of pressure and temperature. According to Henry's Law, the solubility of a gas in a liquid is directly proportional to the pressure of that gas above the liquid; this addresses how pressure affects solubility. Regarding temperature, typically for gases, increased temperature results in decreased solubility.

Step 2: Examine Statement (a)

Statement (a) suggests that solubility of gas in water increases with temperature. This is typically untrue for gases since increasing temperature usually causes the gas molecules to become more energetic and escape from the solution.

Step 3: Examine Statement (b)

Statement (b) posits that a more polar gas will be less soluble. However, in reality, the polarity of a gas increases its solubility in water, since water is also polar and 'like dissolves like'.

Step 4: Examine Statement (c)

Statement (c) claims that solubility increases with the increase in pressure. This is correct according to Henry's Law; higher pressure above a liquid increases the gas's solubility in that liquid.

Step 5: Examine Statement (d)

Statement (d) declares that solubility is always an endothermic process. This is not true; solubility can be exothermic or endothermic depending on the nature of the solute and solvent involved.

Key Concepts

Henry's Law

In the fascinating world of chemistry, Henry's Law offers insight into how gases dissolve in liquids. Imagine a bottle of soda; when it is sealed, the pressure of carbon dioxide gas over the liquid keeps those bubbles in the soda. When you open the bottle, the pressure is released, and the gas escapes, leading to a fizzy overflow. This is an everyday example of Henry's Law in action.

Formally, Henry's Law states that the amount of dissolved gas in a liquid is proportional to the pressure of that gas above the liquid. Mathematically, the relationship can be described by the equation: \( C = kP \), where \( C \) is the concentration of the dissolved gas, \( k \) is Henry's Law constant, and \( P \) is the partial pressure of the gas. Each gas has a unique \( k \) for a given liquid, which can change with temperature. So, when the pressure is increased, more gas dissolves until a new equilibrium is reached.

Pressure Effect on Gas Solubility

Pressure plays a pivotal role when discussing gas solubility in water. Adding on to our understanding from Henry's Law, it's noteworthy that for a given temperature, an increase in pressure over the surface of the liquid will typically result in more gas dissolving in the liquid—this is why carbonated beverages are bottled under high pressure.

It's essential to realize that this effect is specific to gases; solids and liquids aren't significantly affected by pressure changes because their particles are already very close together. In an educational context, this concept is crucial in fields like oceanography, where deep-sea conditions exhibit high pressures affecting the solubility of gases in seawater.

Temperature Effect on Gas Solubility

When we turn our attention to temperature effects on gas solubility, we witness an inverse relationship compared to solids. As the temperature increases, gases tend to become less soluble in water. This phenomenon occurs because increased temperature gives gas molecules more kinetic energy, allowing them to escape the liquid more readily.

Think of a warm soda bottle—it loses its fizz quicker than a cold one because the gas escapes faster. This concept is widespread in environmental sciences, too, where the temperature of bodies of water affects the dissolved oxygen levels, influencing aquatic life sustainability.

Polarity and Solubility in Chemistry

Delving into the relationship between polarity and solubility reveals the 'like dissolves like' principle. This means that polar substances tend to dissolve well in polar solvents like water, which is itself polar. Conversely, nonpolar gases are not very soluble in water because their molecules do not form hydrogen bonds with water molecules.

The lesson here is that the solubility of a gas in water increases with its polarity. In layman's terms, more polar gases are like guests who thrive at social events—they mix well. Meanwhile, nonpolar gases are the loners at the party, not mingling much with the water molecules. This principle is fundamental to understanding solutions in chemistry and designing processes such as water purification systems.