Page 24 - Curriculum Visions Dynamic Book

Properties of salt
Salt, sodium chloride, is use widely for cooking, preserving and also for preventing roads from icing up. This is because it has a number of unusual properties, as described on this page.
How salt changes the way food cooks
A 10°C rise in temperature doubles the rate of chemical reaction. Salt raises the boiling point of water by several degrees and so the chemical reactions that occur when food is cooked happen at
a higher temperature, and therefore faster. The higher cooking temperature
also tenderises the food more effectively than when cooked at a lower temperature.
Salt also affects the taste of the food because we have taste buds that can detect salt. However, this is a separate effect.
Ice preventer
 Salty water boils at a much higher temperature than pure water as shown by this simple demonstration with salt, water, a beaker and a thermometer.
The temperature at which water turns from a liquid to a solid is 0°C. Any impurity in the water will, however, lower the freezing point. Salt is used because it is a convenient and cheap material that will dissolve in water and add the necessary impurities. The more salt that dissolves in water, the lower its temperature can fall without freezing. Rivers, for example, contain less salt than the sea and so freeze at a higher temperature.
Icebergs can co-exist with sea water in cold environments.
The iceberg is made of pure rainwater which freezes at a higher temperature than the salty sea water. In fact, because the seas near Antarctica have very little rainfall, the sea water is particularly salty and so freezes well below 0°C.
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