Yes, adding salt to ice lowers the temperature of the ice-water mixture. It doesn't make the ice itself colder, but it significantly reduces the temperature of the surrounding water.
How Salt Lowers the Temperature
The process involves a phenomenon called freezing point depression. Salt dissolves in the thin layer of water naturally present on the surface of ice. This saltwater solution has a lower freezing point than pure water. Because the temperature of the ice and water mixture is already at 0°C (32°F), the presence of salt forces the ice to melt to try to reach equilibrium with the lower freezing point of the saltwater. This melting process absorbs heat from the surroundings, including the remaining ice, thus lowering the overall temperature.
- Sources: Multiple sources confirm this. For example, ThoughtCo states that adding salt to ice water can lower the temperature "from freezing or 0 °C to as low as -21 °C". ScienceNotes explains that melting is an endothermic process, meaning it absorbs heat and thus lowers the temperature.
Practical Applications
This temperature reduction is utilized in various applications:
- Ice Cream Making: Salt is often added to ice baths used in ice cream making to reach temperatures below 0°C, facilitating faster freezing.
- De-icing Roads: Salt is spread on icy roads and sidewalks to lower the freezing point of water, causing the ice to melt.
It's important to note that while the overall temperature decreases, the salt doesn't directly cool the ice. The cooling effect is indirect, resulting from the energy absorbed during the melting of ice in the presence of salt.
Misconceptions
Some sources incorrectly state that salt makes ice colder. While the resulting mixture is colder than pure ice water, the ice itself doesn't change temperature, rather its melting point is lowered by the salt, causing ice to melt and further reduce the temperature.
