Cold Facts About Saltwater
When water freezes, individual molecules arrange themselves into a crystal lattice formation. The presence of sodium and chloride ions interferes with this process, which means the temperature needs to be lower for saltwater to freeze. The homemade ice cream concept also applies to salt dumped onto roads during winter months -- salt chunks hinder ice formation on the road surface.
Pure Water Vs. Seawater
Pure water freezes at zero degrees Celsius (32 degrees Fahrenheit). Ocean water generally freezes around negative 2 degrees Celsius (28.4 degrees Fahrenheit). At the extreme end of freezing point depression, water in the Dead Sea is so salty that it freezes at negative 21.1 degrees Celsius (negative 6 degrees Fahrenheit).