Melting ice cubes

Question

Two identical ice cubes are placed in two large containers, one containing tap water and the other containing a strong saline solution. Both liquids are of equal volume and at the same room temperature. In which container will the ice cube melt faster? What will be the main reason for the different dissolution times?

Answer 1

The ice in the saline solution will melt faster.

Salt (NaCl) is an ionic compound, so when it dissolves into water, Na+ and Cl- ions will be in the solution. Since water is a polar chemical, the salt ions will make a weak bond with the water molecules - preventing them from bonding with other water molecules, halting the formation of more ice.

On the surface of ice, there is a sort of equilibrium happening, with the top of the ice melting and refreezing constantly, even when it looks completely solid. With the salt in solution now, the rate of freezing is much less than the rate of melting, causing the ice cube to melt faster.