If you compare the composition of water before and after it is boiled, it will be different. To make coffee you should start with cold water rather than hot or previously boiled water since they will have different tastes. So the difference in freezing temperatures could be because the composition of boiled water is different than the original sample.
A test for this would be to have two water samples. Boil one and let it cool back to room temperature. Then freeze it along with the unboiled sample and see if one freezes first.
Yes, that makes some sense. However, the claim is warm, unboiled water also freezes faster than cool water. (35 degrees C! vs. 5). Also, Cecil failed to duplicate the effect even when he use boiled water that had cooled:
One problem with this statement is that the average temperature of water has little effect on the cooling rate. So you can have two samples, both with average temp of say 15 C. But one of them has surface temp of 30 C and will cool faster than the other one with surface temp of only 20 C.
You should read the original paper, it is linked on the wiki page.
I think that is nonsense. For the water to freeze it must all drop to 0C. Now if you’re talking about an open container made of material that has some insulating properties, the top may freeze first, changing the pattern of freezing, but unless there is a loss of water due to evaporation, that won’t help. And I suspect (but don’t know), that having the surface freeze first in any circumstance will slow down the freezing process.
No, water has maximum density at about 4C, which then sinks to the bottom. It is perfectly possible for ice to form on the surface of water that has average temperature 0-4 C.