What is the white powder strewn onto the streets when snow falls?
Q. What is the white powder strewn onto the streets when snow falls?
- A. That white powder is salt.
- However, this salt is not the type of salt used for cooking.
If so, why are the streets strewn with salt when snow falls?
This is to prevent snow from turning into ice.
Snow accumulates on the streets and during the day, the sun's rays melt these snow and they turn into water. At night, the temperature drops to 0°C, which is the freezing point, and the water turns into ice. The next morning, the streets are slippery with the ice covering them.
Preventive snow from turning into ice helps to prevent pedestrians from slipping and hurting themselves. Water containing salt only turns to ice at a temperature lower than that needed for water to turn into ice. This is why when it snows, salt is strewn onto the streets to prevent the snow from turning into ice during the night.
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What is the meaning of "freezing point"?
The freezing point is the temperature at which water changes from liquid (water) to solid (ice).
Dissolving something (e.g., salt or sugar) in the water lowers the freezing point below 0°C. This phenomenon is called "cryoscopy."