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Kettle Bubbles

 
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Every time I boil a kettle for tea/coffee for my fellow slaves where I work something has been perplexing me.

The bubbles when it boils appear to come from the bottom of the kettle or the water itself.

1) Whats in the bubbles?
2) Does this mean the boiled water is depleted of whatever element/s that make up the bubbles.?
3) Why doesn't the volume of water go down much more than just the amount due to the steam (lots of bubbles= lots of volume?).

Thanks to anyone who is bored enough to reply.
 
Rancher
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When water boils it gets converted from liquid form to its gas form (ie steam). It take energy to do this. When a water particles get enough energy, it is ready to become a gas, but a single gas particle in the middle of liquid doesn't last long - it bounces into liquid-water and gives up some of its energy until it loses the energy it needs to be a gas.

But, if enough of these energetic water molicules gather close enough, they can force the water back and form a tiny bubble. An important factor is the distribution of energy - at some time there will be some particles with little energy, some with lots, and the majority in the middle. As the total energy raises by being heated, you increase the proportion with enough energy to form a gas, increasing the probability that bubbles will survive.

On a side note, the rushing sound you hear in a kettle before you see and singns of boiling are actually the first tiny bubbles tarting to form, but collapsing before they show.

Water enpands as it it heated, and bubbles push the other liquid away, so in the initial stages of boiling you get a rise in the water level, but this drops as the water evaporates.

One extra point is neuclation centers (sp?). This is a fancy term for saying that there are areas that high energy particals can use to help them form bubbles. One easy way to see this is areas in chapagne where bi=ubbles always form. There may be a tiny impurity or imperfection in the glass or liquid aiding the formation of bubbles. An experiment I don't suggest you perform involves placing two cups of water in a microwave - one woth tap water and the second with distilled water. Run the microwave till the tap water boils. At this stage the distilled water has enough energy to boil, but the lack of neucleation pooints allows it to reach a 'superheated' state without boiling. Here's the dangerous don't try this at home part - if you use a long utensil to drop in an impurity, the liquid with start to boil violently. Sugar cubes are a good medium. If you are too close you'll get badly burnt.

Anything else to say about boiling water?
 
Graham VMead
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Marvellous!

Great explanation David and a possibly life threatening experiment thrown in as well.

So the bubbles that make it out of the top then become the steam, i.e they are bubbles of steam!

I'm off to the Kitchen/Lab to find another mystery.
 
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At about 40 Celcius you'll start to see small bubbles rising through the water.
This is the result of some dissolved gasses gassing out (hot water can hold less dissolved gasses than can cold water).
This is mainly nitrogen.

Then when it boils you'll get larger bubbles of water vapour.
 
David O'Meara
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Possibly not life threatening, but certainly able to do great harm.

If you've seen the show 'Mythbusters' they do this as one of their microwave experiments in their first season. I'd heard of it but never seen it done before.

The experiment I want to see is the opposite. You can apparently 'superfreeze' water to below zero celcius without it turning to ice, then drop in a grain of sand and it turns (instantly?) to ice. That sounds kinda fun and not so dangerous - unless maybe you decide to start the process by sticking your hand in there.
 
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