|
Sci Tech
During winter, in the U.S. people add salt to melt the unwanted snow (on the roads). But in India, to make ice-cream we were advised to add salt to the ice cubes amongst which the ice-cream is kept. Can anyone explain the role of salt in these situations?
Sushila Swaminathan, Madurai
ANSWER: We can use salt to melt ice on sidewalks and roadways. The phenomenon is related to a property of solutions. On contact with ice, same of the salt dissolves. The salt solution produced has a lower freezing point than the pure ice and exists as a liquid at a lower temperature than pure water. So, even on a cold day, the ice on a sidewalk will melt if it is brought into contact with salt.
To freeze the salt solution a very low temperature than the temperature required to freeze ordinary water is needed. The ice-cream containers are usually surrounded by the ice cubes which are made out of salt water. This is because these ice cubes help to retain the frozen state of ice-cream inside for a long time. They do this by their gradual melting by way of absorbing any external heat. This helps to maintain the low temperature required for the ice-cream kept inside.
In the ice plant the brine tank which surrounds the cans which hold the ice is filled with salt water. The refrigerating coil is immersed only in the brine tank. The wet ammonium vapour, when it passes through the coils vaporizes completely. The heat required for vaporization being withdrawn from the surrounding brine. Since the salt has the ability of lowering the freezing point, the brine water will not solidify easily. This enables the water present in the cans which are suspended in the brine, to get cool quickly and freeze into ice while the brine water retains its liquidity.
S. Palaniappan, Pudukkottai, T.N.
Send this article to Friends by
E-Mail
Sci Tech
|
