Question

How does sprinkling of salt help in clearing snow-covered roads in hilly areas? Name the colligative property involved.

Hint:

$CaCl_2$ ($i=3$) is more effective than NaCl ($i=2$) for deicing roads.

Answer 1

Step 1: Concept
Salt is an electrolyte and dissolves in the thin film of water on the snow surface, forming a solution.

Step 2: Analysis
When salt (NaCl or $CaCl_2$) is added, it dissociates into ions, significantly increasing the number of dissolved particles. This lowers the freezing point of the solution well below 0$^\circ$C (depression of freezing point). As a result, the snow/ice melts even in sub-zero temperatures because the solution's freezing point is now lower than the ambient temperature.

Step 3: Conclusion
The colligative property responsible is depression of freezing point ($\Delta T_f = i \cdot K_f \cdot m$).

Final Answer: Salt lowers the freezing point of water (depression of freezing point), melting snow at sub-zero temperatures. Colligative property:

Depression of Freezing Point.