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: What happens when salt dissolves in snow water.
Salt (NaCl or $CaCl_2$) dissolves in the thin film of water on snow and dissociates into ions, increasing the total number of dissolved particles.
Step 2: Colligative property involved.
Adding a non-volatile solute to a solvent lowers the freezing point. This colligative property is called depression of freezing point: $\Delta T_f = i \cdot K_f \cdot m$.
Step 3: How this melts snow.
The freezing point of the salt solution falls well below $0^\circ C$. Since the ambient temperature in hilly areas may be above this new lower freezing point, the snow-ice mixture melts.
Step 4: Conclusion.
Salt causes depression of freezing point of water, melting snow even at sub-zero temperatures. Colligative property involved: Depression of Freezing Point.