Why Does Boiled Water Freeze Faster?

Why does boiled water freeze quicker than tap water?Because you have boiled off some chemical impurities ?What of the urbam myth that BOILING water freezes quicker than cold ?
- notley (age 101)
UK

The only "impurities" removed in the water left behind after some of it boils away are dissolved gases, mainly nitrogen and oxygen. Like other dissolved molecules these do lower the freezing point. So removing them does raise the freezing point and can speed up the freezing. Under some circumstances (e.g. surroundings just barely cold enough to freeze pure water) that could lead to the initially boiling water freezing before some water that started colder. So it may not be a pure urban myth, even if the explanations sometimes given are nonsense.

Mike W.

p.s. see https://van.physics.illinois.edu/qa/listing.php?id=1665

(published on 05/07/2016)