Boil Water Below Normal Boiling Temperature

Intro: Boil Water Below Normal Boiling Temperature

As a fun science demonstration, we're going to boil water at about 128F or 53C, significantly below the 212F or 100C that is normally needed, in a syringe.  The water will simply come from a household hot water tap.  The trick is that the boiling temperature of a liquid goes down as the air pressure goes down--water boils when its vapor pressure exceeds the air pressure.

This is a good demonstration to show to kids at home or at a school.

What you need:

• Plastic syringe  (I used a 12mL monoject.  One can buy them cheap in large or small quantities on amazon or ebay.)
• Hot tap water, at around 125F
• Cup for the water
• Optional: Thermometer

STEP 1: Pour Water Into Cup

Run hot water from the tap, waiting for it to reach full temperature.  Then fill up a cup with the hot water.

Stick a thermometer into it if you like.  But don't take too long, or the water will cool off too much.

STEP 2: Put Water in Syringe

Gently fill the syringe a little less than 20% full (I put 2mL of water in a 12mL syringe).  If you want, you can put a little more in, and then eject bubbles by holding the syringe pointing up and pushing the piston up.

STEP 3: Boil the Water!

Press one finger very tightly over the tip of the syringe.  Hold the syringe horizontally, and pull back the plunger to the full length of the syringe, gently so it doesn't pop out (it'll take some force).  If all goes well, the water should boil for a few seconds along the length of the syringe.  You may also notice the syringe steaming up.  

Then gently release the syringe.  You should notice that everything returns to more or less how it was before the experiment (maybe with a little bit more air, if some leaked in).

It should also boil if you hold the syringe vertically.  But then you or your audience might worry that the bubbling is not boiling, but it's just air leaking in and around the piston.

If it doesn't boil, try using less water.  Or hotter water.  Or alcohol (e.g., heated by putting a small cup of alcohol in a larger cup of hot water).

Comments

[Computothought]

Would be interesting to do that with a large pvc equivalent of the small syringe. Might actually be useful for camping or picnics.

[arpruss]

You mean, for disinfecting water? I am not sure low-temperature boiling will disinfect. Or is there some other purpose to boiling?

[Computothought]

You could have a can of soup or whatever suspended in the tube. when the water boils, the food in the can gets cooked (patent pending).

[The Ideanator]

Not going to work.

The water is boiling due to the low pressure, taking that a step further, it would require a higher temperature to boil water in a higher pressure.

[mountainman123]

Maybe, those bubbles are just from air leaking around the plunger's seal. That is my bet!
What would be interesting to do is, record the same viedo with a thermal imaging camera!

[arpruss]

This hypothesis can be tested: just use a lower temperature. There shouldn't be a big difference as to how much water at 30C and at 50C leaks. And from what I remember, with lower temperature water nothing much happened.

Also, if you look at the step 3 photo, the bubbles are all through the water, not just near the plunger. Bubbles from the plunger would be going straight up, not to the left.

And when you look at it, it's obviously boiling. :-)

[arpruss]

The water is boiling at 50C. That's not enough to cook the soup.

[Computothought]

Sure you are right, but most soups in a can are already cooked and just need some heat.

[arpruss]

But you're not actually generating any heat in this way. In fact, the boiling takes heat out of the water. So you might as well put it in the water without any low pressure tricks. Not that I wouldn't mind a use being found for this!