Does anyone here know the freezing point of pure H2O? (Hint) It's not 0 degrees Celsius or 32 degrees Fahrenheit..
At one atmospheric pressure, those are considered to be the melting points. So I'm guessing that you want an answer a hair below those numbers?
they are the melting and freezing points, its a plateau really, both ice and water exist at 0 degrees C. That is both the melting and freezing point of pure H2O so i'm not too sure where you're coming from OP
Pure H20 freezes at -40 degrees C. Which is conveniently exactly the same temperature as -40 degrees F. The reason that the water we encounter freezes at 0 degrees is because the impurities in it act as a catalyst in ice nucleation.
dont solutes lower the freezing point of water, such as salting roads to make it stay water rather than ice?
Nope. Sure water freezes at -40, but it'll freeze way before that too. And lol @ impurities acting as a catalyst.
Sure, but if it's perfectly still it can freeze at as low as -40 degrees. And lol am I wrong? the reason the ice nucleates at 0 degrees is because of impurities in the water. Even if you distill the water, it's still not pure H20. You'd have to go through several distillations or a simple chemical equation to get pure water.
I'd need to see some literature on that, please What impurities are you discussing, that need to be pulled from pure water? I already knew it was incorrect (you had me second guessing myself there for a second though), but out of curiosity I just googled 'pure water freezes -40' and came up with ZERO results. I think you're somewhat confused. Of course water can freeze at -40.. because pure water freezes at all the temperatures between there, and 0 c The less pure, depending on the level of impurity and what that impurity is, the lower the temp you normally need in order to achieve ice. Salt water for instance, or water made impure by salt, doesn't freeze until it reaches much lower temps, the more pure the water, the higher the temp it will solidify at up until a certain point, and at an average atmospheric pressure. This is why we throw salt on iced roads and pathways, in the winter. Freezing point of salt water « The Official MartinZ Blog Q & A: Freezing Saltwater | Department of Physics | University of Illinois at Urbana-Champaign Freezing-point depression - Wikipedia, the free encyclopedia " Freezing-point depression describes the phenomenon in which the freezing point of a liquid (a solvent) is depressed when another compound is added, meaning that a solution has a lower freezing point than a pure solvent. This happens whenever a solute is added to a pure solvent, such as water. The phenomenon may be observed in sea water, which due to its salt content remains liquid at temperatures below 0C (32F), the freezing point of pure water." In other words: impure water requires lower temps to freeze, while pure water still becomes ice at roughly 0c/32f at an average atmospheric pressure.
As the ice began to freeze water, the fraction of water in the solution becomes lower, and further down to freezing! However, this does not continue. At some point become saturated salt solution.
As others have stated, this is very wrong. I'm not sure where you got your information, but if it's your high school chemistry teacher, he/she should be fired. The original definitions of 0C and 100C were the freezing and boiling points of PURE water, respectively. Now days, the formal definition is slightly different (more robust one might say), but for most intents and purposes the original definition is still valid. And impurities don't "catalyze" ice nucleation. They prevent it, as others have said.
The freezing point or melting point of water is the temperature at which water changes phase from a liquid to a solid or vice versa. The freezing point describes the liquid to solid transition while the melting point is the temperature at which water goes from a solid (ice) to liquid water. In theory, the two temperatures would be the same, but liquids can be supercooled beyond their freezing points so that they don't solidify until well below freezing point. Ordinarily the freezing point of water is 0 C or 32 F. The temperature may be lower if supercooling occurs or if there are impurities present in the water which could cause freezing point depression to occur.
Freezing supercooled water puzzles scientists What is unfreezable water? Is it the same as bound water or water of hydration? Nucleation - Wikipedia, the free encyclopedia "Pure water freezes at −42C rather than at its freezing temperature of 0C if no crystal nuclei, such as dust particles, are present to form an ice nucleus" "Consequently, pure water can be cooled well below zero (sometimes to -40C) before ice forms" " It has been known for centuries that pure water, in the absence of any nucleating surface, can remain in a supercooled liquid state down to temperatures as low as -40C." I'll admit my first post was pretty ignorant in that I was stating that all pure water, everywhere, freezes at exactly -40 degrees and no other temperature. What I meant was that it's possible for pure water to be cooled down to about -40 degrees before it freezes, in the absence of any crystal nuclei to form an ice nucleus.
That's a little bit different; taking a rare circumstance, altering the environment, in order to reduce the liquid point of water, and where we already mentioned freezing depression (the ability to reduce the termperature of liquid water, without inducing freezing) and how it can be caused... it's not quite the same as what you were saying earlier, that all pure water freezes at -40, and that if it freezes earlier or warmer, it's not pure. But it's good you realize that now Apples and oranges, it is interesting, but less interesting than we were hoping for where you can accomplish the same outcome with a little salt Under normal circumstances, or those we run into on a day to day basis, pure water is still going to freeze at 0 c and 32 f