We did a little kichten experiment today where we put ice cubes in glasses of water. We had one glass with normal tap water and 5 glasses which increasing concentrations of salt water. My hypothesis was that the ice in the salt water would melt faster because the salt lowers the melting point of water.
What I observed however was that the ice in the water without any salt melted much faster then in the salty water. Can anyone explain why this happened? How is this experiment different from salt that is spayed on roads during the winter to melt snow and ice?
Edit: some more details
The glasses were all the same size and all had the same amount of water (around 150ml). All glasses were filled from the same can with tap water to make sure they had the same starting temperature. The first glass had no salt, the second one table spoon of salt, then two table spoons etc. After mixing the salt by stirring slowly we added one ice cube of 20 grams to each glass and left the glasses in the kitchen at room temperature.
After about 40 min the ice in the glass without water had melted completely while all the others were all still about half the original size.
Best Answer
There’s a great answer to this here: https://mirjamglessmer.com/2013/09/04/ice-cubes-melting-in-fresh-water-and-salt-water-post-24/. In summary, when the ice is placed into salt water, the cold melted water from the ice is less dense than the salt water so it stays at the top with the ice, preventing warm salty water from further melting the ice cube. When ice is placed into freshwater, the melted water from the ice sinks (since it is more dense than the warm freshwater), and more warm freshwater can surround the ice, further melting the ice.