Question

People add sodium chloride to water while boiling eggs. This is to (a) decrease the boiling point of water (b) increase the boiling point of water (c) prevent breaking of eggs (d) make eggs tasty

Short answer

(b) Increase the boiling point of water.

Step-by-step solution

Understanding the Problem

We need to determine why people add sodium chloride (table salt) to water when boiling eggs. We are given four options to choose from.

Boiling Point Concept

Adding a solute such as salt to a solvent like water will cause the boiling point of the water to increase. This is known as boiling point elevation.

Checking Option (a)

Option (a) suggests that adding salt decreases the boiling point of water. This is incorrect because adding salt actually increases the boiling point.

Checking Option (b)

Option (b) suggests that the purpose is to increase the boiling point of water. Since adding salt does increase the boiling point, this option is technically correct.

Checking Option (c)

Option (c) proposes that adding salt prevents eggs from breaking. While salt water heats up faster, there's no direct correlation with preventing egg breakage.

Checking Option (d)

Option (d) indicates that salt makes the eggs tasty. This isn't the primary reason people add salt during boiling.

Conclusion

The most accurate answer based on scientific principles is option (b): to increase the boiling point of water.

Key concepts

Sodium Chloride Effect

When we add sodium chloride (table salt) to water, it affects the water's boiling point. This is known as the Sodium Chloride Effect in everyday terms. Many people might wonder why salt is added to boiling water, particularly when cooking dishes like eggs. The answer lies in how salt interacts with water molecules. Adding sodium chloride disrupts the hydrogen bonding between water molecules. This makes it harder for water molecules to escape as vapor, thus elevating the boiling point. This effect means more heat is required to bring the water to a boil compared to pure water. When you're cooking, understanding this effect can be useful. For instance, infusing salt into water before boiling can slightly increase the temperature, leading to more thorough cooking in some recipes. Though the change is not drastic enough to be the primary reason in everyday cooking, it does provide a scientific foundation.

Colligative Properties

To understand the sodium chloride effect, we need to delve into the realm of colligative properties. These are properties that depend on the concentration of particles in a solution rather than the type of particles. Boiling point elevation is part of these colligative properties. As soon as a non-volatile solute like sodium chloride is added to a solvent such as water, the boiling point increases.The reason colligative properties are interesting is they are universal for all solvents mixed with non-volatile solutes. Whether you're adding sugar or salt, the boiling point elevation can be predicted based on the formula:\[\Delta T_b = i imes K_b imes m\]Where \( \Delta T_b \) is the boiling point elevation, \( i \) is the van't Hoff factor (for sodium chloride, it is 2 because it dissociates into two ions), \( K_b \) is the ebullioscopic constant of the solvent, and \( m \) is the molality of the solution. This formula shows that the elevation depends only on the number of solute particles.

Solute and Solvent Interactions

Understanding the interactions between solute and solvent is crucial when studying boiling point elevation. Water, as a solvent, has strong hydrogen bonds. When a solute like sodium chloride is added, it disrupts these interactions. Water molecules are surrounded by chloride and sodium ions. This new interaction pattern means more energy is needed for water molecules to transition from liquid to gaseous state, hence the boiling point increases. This disruption of water's structure affects how molecules behave at the surface. The additional kinetic energy required for boiling comes from heat, which changes the cooking dynamics slightly. In practical terms, although this might not hugely impact everyday cooking, knowing this biochemical interplay explains why boiling conditions change subtly.

• Solute particles increase the energy required to change phase.
• Ionic solutes like sodium chloride significantly affect these interactions due to their charge.
• The effects can be quantitatively predicted using colligative property formulas.