MCQ Detailed View

In cold countries, during winter, roads often become covered with ice, creating dangerous and slippery surfaces for vehicles and pedestrians. To solve this problem, a common method is to spread salt on icy roads. The reason salt is used lies in a scientific principle known as freezing point depression, which is a concept from chemistry.

Water normally freezes at 0°C (32°F). When salt, usually in the form of sodium chloride (NaCl), is added to ice, it dissolves into the thin layer of liquid water that is always present on the surface of ice. This creates a saltwater solution. A saltwater solution has a lower freezing point than pure water, meaning it needs a colder temperature to remain frozen. As a result, the ice begins to melt even though the temperature may still be below 0°C.

Salt is the most commonly used substance because it is inexpensive, readily available, and highly effective in lowering the freezing point of water. Other substances like sand may be used to increase friction on icy roads, but sand does not melt ice. Chemicals like calcium chloride or magnesium chloride can also be used, as they work at even lower temperatures than regular salt, but they are more expensive.

Chlorine and carbon dioxide are not suitable for melting road ice. Water, when added, simply freezes again under low temperatures, making the road more slippery. Salt remains the best choice because of its ability to disrupt the natural freezing process of water, preventing ice from forming and helping already formed ice to melt.

This simple chemical reaction saves lives by improving road safety during harsh winters, demonstrating a practical, everyday application of chemistry in real life.