What Water Will Freeze First? Tap, Salt, Or Sugar?

The tap water will freeze first, then the sugar water, and the salty water will freeze at the end. In fact, when you add a solute to water, it lowers its freezing point. So you have to lower down the temperature to freeze the water. This is called as "freezing point depression". It is "colligative property" of water. The reason why tap water freezes first is that, tap water does not contain minerals/chemicals/solutes in heavy quantity. So there are less solute particles to depress the freezing points, so the freezing point will reach earlier (at little lower than 0 degree Centigrade). But then sugar molecules will depress the water freezing point even further. So if you have added 1 mole of sugar to water, the water will freeze later (at -1.8C). In the case of salt,one molecule contains two ions i.e Na+ and Cl-. So when you add 1 mole of salt in water, two moles of ions (1 mole of Na+ and 1 mole of Cl-) are present in the water. So there are more molecules of solute to depress the freezing point more than the sugar's 1 mole does. So the water will freeze at -13.6C.
I hope you got the whole idea about freezing point depression:)

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