Understanding the Boiling Point of an NaCl Solution: Why It’s 100°C and Not 1465°C

The common conception is that the boiling point of a sodium chloride (NaCl) solution is 100 degrees Celsius, the same as pure water. However, this is often misleading, especially when considering the context of how boiling points are defined for different substances. Understanding the true boiling point of NaCl solutions, and the conditions under which the boiling and melting points of pure NaCl differ, can provide valuable insights for both educational and practical purposes.

Boiling Point of Water

It is a well-known fact that the boiling point of pure water (H2O) is 100 degrees Celsius at one standard atmosphere (1 atm) of pressure. This is a critical point in many chemical and biological processes, and it forms the basis for the boiling point elevation phenomenon observed in solutions containing solutes.

Effect of Solutes on Boiling Point

When sodium chloride (NaCl) is added to water, it dissociates into sodium (Na ) and chloride (Cl-) ions. This process increases the number of particles in the solution, which leads to a higher boiling point compared to pure water. This phenomenon, known as boiling point elevation, is a colligative property of solutions and can be explained by the Raoult's Law and the Van't Hoff factor.

The boiling point elevation can be calculated using the formula:

ΔTb i · Kb · m

ΔTb change in boiling point i Van't Hoff factor for NaCl i 2 because it dissociates into two ions (Na and Cl-) Kb ebullioscopic constant of the solvent (water in this case) m molality of the solution

For typical concentrations of NaCl in water, the boiling point is slightly elevated above 100 degrees Celsius, but it will not reach extreme temperatures like 1465 degrees Celsius. This is important to understand for accurate experimental design and safety measures in laboratory settings.

Melting Point vs. Boiling Point

The figure of 1465 degrees Celsius refers to the melting point of solid sodium chloride (NaCl), not a solution. To change from solid to liquid state, NaCl itself must be heated to this high temperature, approximately 801 degrees Celsius. In contrast, when dissolved in water, the properties of the solution differ significantly, and the boiling point is relevant only when water remains in the solution. Once the water evaporates, the remaining solid NaCl can be heated further to its boiling point, around 1413 degrees Celsius, which is close to the 1465 degrees Celsius mentioned.

In summary, the boiling point of an NaCl solution is around 100 degrees Celsius due to the properties of water and the effects of solutes, while 1465 degrees Celsius is the melting point of solid NaCl. Understanding these distinctions is crucial for accurate scientific calculations and observations.