Introduction

Relevance of the Theme

Boiling Point Elevation is one of the central pillars of Colloidal Chemistry, a name that refers to the study of properties that vary, depending on the quantity and size of dispersed particles in the medium. Discussing Boiling Point Elevation leads us to a deeper understanding of how solutions operate at a molecular level, affecting the boiling temperature.

This is a subject of fundamental importance in Chemistry, as it is not restricted to a specific topic, but is crucial for understanding the physical-chemical phenomena that occur in numerous processes of our daily lives, such as cooking food and the operation of internal combustion engines.

Contextualization

Boiling Point Elevation fits into the broader context of the study of chemical solutions, which is one of the most significant and extensive areas of Chemistry. This theme is a natural extension of previously studied contents, such as the definition of solutions, Raoult's law, and osmosis, and precedes the discussion of other phenomena of interest, such as cryoscopy (which studies the variation in solidification temperature due to the presence of solute) and osmotic pressure.

The complexity and importance of Boiling Point Elevation lie not only in understanding the formulas but mainly in identifying and interpreting these phenomena in real contexts and solving practical problems. The theme is an essential component for understanding the high school Chemistry curriculum and provides the basis for further studies in Chemistry at the university level.

Theoretical Development

Components

• Boiling Point Elevation: It is the study of the phenomenon that occurs in the increase in the boiling temperature of a pure liquid when a non-volatile solute is dissolved in that liquid. In other words, when a solute is added to a solvent, the resulting substance will have a higher boiling temperature than the pure solvent.

• Molality (m): Molality is a concentration unit that expresses the ratio of moles of solute per kilogram of solvent. Mathematically, it is calculated by dividing the amount of solute in moles by the mass of the solvent in kilograms.

• Molal Boiling Point Elevation Constant (K_b): Each solvent has a characteristic molal boiling point elevation constant, which is the amount by which the boiling temperature of the solvent is raised for each unit of solute molality. The unit of K_b is °C·kg/mol.

• Clapeyron Equation: The Clapeyron formula is an equation that relates the change in vapor pressure with the change in temperature, providing a theoretical basis for understanding boiling point elevation. Mathematically, the equation is expressed as: ΔT_b = K_b * m * i, where ΔT_b is the change in boiling temperature, K_b is the molal boiling point elevation constant, m is the molality, and i is the Van't Hoff factor, which takes into account the dissociation or association of the solute in solution.

Key Terms

• Boiling: Physical process of phase change in which a liquid turns into a gas. It occurs when the vapor pressure of the liquid equals the external atmospheric pressure, and the temperature at the liquid's surface, in other words, throughout its extent, reaches the value known as the boiling point.

• Solution: Homogeneous mixture of two or more substances, in which the substance in lesser quantity, called the solute, is dissolved in the substance in greater quantity, called the solvent.

• Solute: Substance present in lesser quantity in a solution.

• Solvent: Substance present in greater quantity in a solution, responsible for dissolving the solute.

Examples and Cases

• Boiling Point Elevation of Table Salt: A classic example of boiling point elevation is when we add salt - the solute - to water - the solvent - to cook pasta. The addition of salt raises the boiling temperature of water, making the pasta cook faster. This happens because, with salt, water needs to reach a higher temperature to boil.

• Boiling Point Elevation of Ethanol in Gasoline: Another example is the addition of ethanol to gasoline. The presence of ethanol as a solute in gasoline, which is the solvent, increases the boiling temperature of the mixture. This leads to improved energy efficiency and reduced air pollution, as ethanol has a more controlled combustion kinetics than gasoline.

• Boiling at Different Altitudes: An interesting application case of boiling point elevation is the variation in the boiling point of water due to altitude. At higher altitudes, where the atmospheric pressure is lower, water boils at lower temperatures. This happens because the force of the atoms in the vapor does not need to overcome as much resistance from the atmosphere to escape the liquid, therefore, less energy is required, meaning the boiling temperature is lower.

Detailed Summary

Key Points

• Definition of Boiling Point Elevation: It is the phenomenon that studies the increase in boiling temperature when a non-volatile solute is added to a solvent. Because of this, boiling point elevation is one of the colligative properties, which depend on the number of solute particles in solution, not their nature.

• Importance of Molality: Molality is the concentration unit used in the boiling point elevation equation, showing its relevance in calculating the boiling temperature variation. It is the ratio between the amount of solute, in moles, and the amount of solvent, in kilograms.

• Boiling Point Elevation Constant (Kb): This is a specific property of each solvent, indicating the variation in boiling temperature per unit of solute molality. It is used in the boiling point elevation equation to determine the boiling temperature variation.

• Clapeyron Equation: This equation relates the boiling temperature variation (ΔTb) to the solute concentration in molality (m). Additionally, it includes the Van't Hoff factor (i), which takes into account the dissociation or association of the solute in solution.

• Boiling Concept: Boiling Point Elevation is closely related to the concept of boiling, which is the change of physical state from liquid to gas and whose temperature is altered by the presence of a solute.

Conclusions

• Impact of Boiling Point Elevation: Boiling Point Elevation has a significant effect on the physical properties of solutions, especially on the boiling temperature. Understanding this phenomenon is essential for Chemistry, as it allows for a better understanding of the composition and behavior of solutions under different conditions.

• Components of Boiling Point Elevation: To understand and calculate boiling point elevation, it is necessary to consider components such as molality, boiling point elevation constant, and Van't Hoff factor. These components are determined by the characteristics of the solute (number of particles, molar mass) and the solvent (molar mass, physical properties).

• Applications of Boiling Point Elevation: Boiling Point Elevation has several practical applications, such as in the food industry (cooking), chemical industry (separation processes), and in daily life (kitchen and laboratory). Boiling Point Elevation is also important to understand the influence of atmospheric pressure on the boiling temperature (altitude effect).

Exercises

1. Theoretical Problem: Calculate the variation in the boiling temperature of water when 58 g of sucrose (C₁₂H₂₂O₁₁) is added to 500 g of water. Given: Kb of water = 0.512 °C·kg/mol, Van't Hoff factor for sucrose = 1.

2. Everyday Problem: Explain why food takes longer to cook in high-altitude locations.

3. Conceptual Problem: Compare boiling point elevation and freezing point depression. What are the similarities and differences between these colligative properties?