Question

why does ice at 0°c appear colder to the mouth than water at 0°c????

Answer 1

It is due to latent heat of fusion which is about 79 calories (approximately) for conversion of ice into water or vice -versa. Due to this latent heat of fusion when you put ice and water in mouth it took 79 calories more than water at 0 degree celsius in order to became water at 0 degree Celsius . So in first when you put ice mouth then heat absorb by ice is more. So that's why you ice more cold than water at same temp.

Hope this helps.