Melting Ice in water and the final Temperature

[wakejosh]

I have heard that when ice mixes completely with water then the Ice will be completely melted and the temperature of the water willl actually be below 0 C, is this true?

 

[Hootenanny]

I have heard that when ice mixes completely with water then the Ice will be completely melted and the temperature of the water willl actually be below 0 C, is this true?

Yes, it is possible to have water at a temperature less than 0^oC if it has some solute (e.g. salt) dissolved in it, this is known as freezing point depression. In general, the more solute(salt) you add to a solvent(water), the lower the freezing (and hence boiling) point becomes.

 

[berkeman]

But also in the absence of a solute, Icewater should be at 0C while the ice is melting, I believe, since it is at the phase transition temperature. Is that right Hootenanny?

 

[wakejosh]

well, he didnt say anything about ice, one of my freinds says he doesn't think the TA is right, and I don't know how much I trust him either. His observation was in regards to this question:

a 32 oz cup with 8 ounces of ice (250g about .25 liter volume) at zero degrees C is added to 750 g of water at 25 C.

he says that when they have mixed the Ice will be melted and the water can actually be below 0 C, he said nothing about Salt, nor does the problem.

From what you have said it sounds like when they are mixed the Ice will not be compltely melted and the temperature will be about 0 C. you guys think this is more accurate? I do.

 

[Hootenanny]

But also in the absence of a solute, Icewater should be at 0C while the ice is melting, I believe, since it is at the phase transition temperature. Is that right Hootenanny?

This is indeed true, thermal energy is transferred from the water (and other surroundings) to increase the internal energy of the ice. As an aside, I have seen examples where the temperature of pure water (distilled) has been reduced to around -5^oC before any ice has formed, however, once ice is formed the temperature increases again back up to 0^oC.

 

[Hootenanny]

he says that when they have mixed the Ice will be melted and the water can actually be below 0 C, he said nothing about Salt, nor does the problem.

Is the water from a tap or distilled? What are you measuring the temperature with?

 

[wakejosh]

Is the water from a tap or distilled? What are you measuring the temperature with?

none of that was specified in the question.