Distilled Water

[tranceport]

They said that because there was no contaminets in the water it would not boil. Explaing the exploding water out of a microwave when you put your tea bag or spoon or whatever in the water.

The distilled water would be superheated above 212F and would boil violently when a contaminet was inserted.


Why does this occur?


How hot can you get distilled water?




Please forgive any spelling errors.

 

[Calin]

Water has a "triple point" at atmospheric pressure at 0C, or something like 32F. At that point, water can exists simultaneously as solid (ice), liquid (water) and gas (vapors). But back to topic, 100C (or 212F) is the limit when water will transform in vapors (you can call it steam).
Now water boils at 212F, but it will start to boil at (or around) impurities. But uinless those are dissolved into water, those does not affect the boiling point.

So, my answer is no - the only way to "superheat" water is to pressurize it.

Calin

 

[sao123]

Ok, i read this awhile ago, so if im slightly wrong correct the minute details, though the general theory implied is correct.

I believe what you are looking for is surface tension. Heating water in a microwave is fundamentally different than boiling water on a stove.

Heating water on a stove, the heat is transferrer by touch from the pan to the water. The point here is that the water boils first at the surface of the pan, because it has something to seed the steam bubbles on.

Heating the water in the microwave heats the water from the inside out. There is nothing for the steam bubbles to seed on (because in distilled the impurities are removed). Surface tensions stops the bubbles from forming on the open air surface. Therefore bubbles do not form anywhere and the water can get only a few degrees warmer than 212, like maybe 214. then at the point where you pick up the cup, it disturbs the surfact tension, and and boom.... it explodes, due to the instantanious rapid mass boiling.

 

[DrPizza]

Another factor is the smoothness and other characteristics of the vessel it's being boiled in... hence, in chemistry labs, they "seed" boiling with small ceramic chips.

 

[Calin]

The water won't heat much over the boiling point (if any) - the water vaporize even at temperatures close to freezing point, regardless of suface tensions. Also, "water" go directly from solid form to gas form at sub-freezing temperatures.
Anyway, while a very small quantity of water might be just going from liquid to steam, it should be noted that the volumetric increase is something like 600x. So, even a 0.1% of water instantly becaming steam could produce the effect of "explosion"

Calin

 

[Cogman]

I had something like this happen to me. I put some water in a smooth glass to make hot chocolate. After It had cooked for like 3 minuets I took it out and just as soon as I put the Mix in it to boiled very violently.

 

[gururu]

its right that bubbles must form on a rough surface such as on the bottom of a pan. If you dropped a toothpick in a cup of water, then microwaved it, it would boil. water won't form bubbles on very smooth surfaces such as might be found in a cup or bowl. In a lab, sometimes boiling stones are used (small carbonate rocks) to induce boiling. Just because boiling is not visible however does not mean that phase transition is not occurring. However, most of the time the water we use in microwaves isn't pure and will have a boiling point above 100 C.

 

[Cawchy87]

I saw this episode too, didn't really understand it though.

 

[tranceport]

Please keep in mind that distilled water and regular tap water are different..

I tested this with distilled water just like on mythbusters. Distilled water and tap water in the microwave. After about 3 minutes the tap water was at a rolling boil.
The distilled water was not doing anything. I dropped a chicken broth cube in the distilled water. Water immediatly splashed and boiled. Although I do not have a thermometer that goes up to 212F I do belive the distilled water comming out of the microwave after 3 minutes was at or above 212F becuase the tap water which went in at the same time was boiling. Both of these "Waters" felt the same tempt when I put them in.. "Room temp"

 

[harrkev]

How to do this at home:

1) Get a VERY clean VERY smooth container (such as a high-quality coffee cup).

2) Heat the water in a microwave to boiling.

3) Let it cool to room temperature in the microwave (or covered to keep dust from getting in).

4) After cooling, re-heat in the microwave. Heat the same amount of time as step 2. Maybe add in an extra minute for giggles.

5) Drop something granulated in. Sugar or instant coffee should work well.

6) RUN! This stuff will bubble over FAST, and it will be HOT!

I have done this by accident a couple of times, and it works. The key is to heat it first and then let it cool.

 

[CTho9305]

Originally posted by: harrkev
How to do this at home:

1) Get a VERY clean VERY smooth container (such as a high-quality coffee cup).

2) Heat the water in a microwave to boiling.

3) Let it cool to room temperature in the microwave (or covered to keep dust from getting in).

4) After cooling, re-heat in the microwave. Heat the same amount of time as step 2. Maybe add in an extra minute for giggles.

5) Drop something granulated in. Sugar or instant coffee should work well.

6) RUN! This stuff will bubble over FAST, and it will be HOT!

I have done this by accident a couple of times, and it works. The key is to heat it first and then let it cool.

You really shouldn't - there's a pretty good chance it will boil explosively.

Water freezes/boils better when it has a "nucleation point" - something to start a bubble or ice crystal on. When you have a smooth container with clean water, there aren't any nucleation points avaliable for the crystal to start forming (for freezing) or bubbles (for boiling). When you add something else (sugar, dirt) and water is colder than 0 or hotter than boiling it will rapidly freeze or boil.

The reason microwaving water is dangerous is that if there's any dirt/dust on the side of the container, when you pick it up and the water touches the dirt, it can boil suddenly and seriously burn you.

edit: link

 

[Shalmanese]

The safest way to test this at home is to stick a toothpick into the water.

 

[TuxDave]

That's so cool. I need to email my parents about this since I know they microwave water when they just want a small cup of whatever instead of boiling a whole pot.

 

[BadThad]

Originally posted by: DrPizza
Another factor is the smoothness and other characteristics of the vessel it's being boiled in... hence, in chemistry labs, they "seed" boiling with small ceramic chips.

We use PTFE chips these days, more chemically inert.

 

[Peter]

It boils later the 2nd time because the 1st time has driven out all the tiny oxygen "seed" bubbles that were in the container from when you filled it from the tap, and all the steam bubbles have collapsed back into liquid water. So the 2nd time around, there are no seed bubbles in the water, and you'll be able to superheat it.

 

Note to all members who are going to try this:
Do not do so without some sort of protection. Flash boils can be explosive and will create 3rd degree burns. Wear protective gloves if anything. Some sort of face covering would help too.

 

[gyromind]

So would this experiment work equally well with the freezing of water? Say I took that same mug of distilled water and put it in the freezer below 0, could I put a toothpick in that, and watch it freeze before my eyes?

 

[Shalmanese]

There is such a thing as supercooled water. In certain rare occasions, you can stick a bottle of lemonade or beer in the freezer and, when you pop the top, the liquid will instantly foam out as a frozen slush.

 

[gyromind]

That seems more to do with carbonation though.

 

[EULA]

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