Colligative Properties
The difference in boiling and freezing points arises from colligative properties. These are properties of solutions that depend solely on the number of solute particles present, not their identity. The main colligative properties are:
* Boiling Point Elevation: The boiling point of a solution is higher than that of the pure solvent.
* Freezing Point Depression: The freezing point of a solution is lower than that of the pure solvent.
Dissociation and Particle Concentration
* NaCl: When NaCl dissolves in water, it dissociates into two ions: Na+ and Cl-. This means that a 0.10 molal solution of NaCl actually contains 0.20 moles of particles (0.10 moles Na+ + 0.10 moles Cl-).
* C6H12O6: Glucose (C6H12O6) does not dissociate in water. It remains as a single molecule. So, a 0.10 molal solution of glucose contains 0.10 moles of particles.
The Impact on Colligative Properties
Since NaCl provides twice the number of particles in solution compared to glucose at the same molality, it will have a greater effect on the colligative properties:
* Higher Boiling Point: The greater number of particles in the NaCl solution disrupts the vapor pressure of the solvent (water), making it harder for water molecules to escape into the gas phase. Therefore, a higher temperature is required to reach the boiling point.
* Lower Freezing Point: The increased concentration of particles in the NaCl solution interferes with the formation of the solvent's crystalline structure, making it harder for the solution to freeze. This results in a lower freezing point.
In Summary
The difference in boiling and freezing points between a 0.10 molal NaCl solution and a 0.10 molal glucose solution is due to the fact that NaCl dissociates into ions, leading to a higher concentration of particles in the solution. This higher particle concentration has a stronger impact on the colligative properties, resulting in a higher boiling point and lower freezing point for the NaCl solution.
