Question

Sprinkling of salt helps in clearing the snow-covered roads in hills. The phenomenon involved in the process is:
A: lowering in vapour pressure of snow
B: depression in freezing point of snow
C: increase in freezing point of snow
D: melting of ice due to increase in temperature by putting salt

Answer 1

Hint : Salt gets easily dissolved in water. You must recall that the more solute or salt added to water, more is the rise in boiling point. The process depends upon the number of particles that are formed in solution. Elevation in boiling point of a solvent is inversely proportional to its freezing point.

Complete Step By Step Answer:
When salt is added to water, this indicates that dissolved foreign particles have been introduced into the water. Freezing point of the water keeps on lowering as more and more particles are appended till the point when salt stops getting dissolved. This is the reason that salt is employed for melting the ice and snow and also keeps them from re-freezing. Actually, the principle on which salt works is lowering of the melting or freezing point of the water. This effect is known as depression in freezing point. A compound which yields more ions into a solution of water lowers the freezing point of water more. For example, calcium chloride ($CaC{l_2}$) yields three ions (i.e. one calcium and two chloride ions) when dissolved in water and thus, lowers the freezing point of water more in comparison to sodium chloride ($NaCl$) which yields two ions (i.e. one sodium and one chloride ion).
Depression in freezing point is directly proportional to the molality of the added solute. The formula used is:
$\Delta {T_f} = i \times {K_f} \times m$
Where, $\Delta {K_f} =$ depression in freezing point
$i =$ Van’t Hoff factor
${K_f} =$ cryoscopic constant
$m =$molality
As a result sprinkling of salt helps in clearing the snow-covered roads in hills. The phenomenon involved in the process is depression in the freezing point of snow.
Thus, the correct answer is Option B.

Note :
Freezing point depression is considered to be a colligative property of water. Colligative property depends upon the number of particles present in a substance. All liquid solvents having dissolved particles demonstrate the colligative property. Other colligative properties are elevation in boiling point, lowering of vapor pressure and osmotic pressure.