Freezing Point of Water

i have done solidification experiment of water in my lab (national institute of technology rourkeka)inside a copper block and the copper block was cover by liquid nitrogen. we found that water solidify between 5 to 0 degree.i have done more than 100 experiment but every time i found that water solidify in the range of 5 to 0 degree centigrade. now i am confuse how water could solidify at 5 t0 0...............?please clear
- laxman chauhan (age 26)
india

This is indeed a puzzle. If the water is in a sealed chamber with some gas, cooling will cause the pressure to drop, which does raise the freezing point a bit. The highest it can go is the triple point, at 0.01°C, which is hardly a noticeable amount above 0.00°C. 

My guess is that somehow your thermometer is not reading correctly. If the cooling is rapid, there can be big difference in the  temperature between different regions. Perhaps there's a way to cool much more slowly. You might let cold nitrogen gas flow all over the copper block and see if you get a different result.

Another possibility is just that the thermometer is mis-calibrated. Have you tried putting it in an ice-water bath to make sure it reads 0°C?

Mike W.

(published on 03/09/2015)