Re: pinhole rising water level science

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From: pauld@exploratorium.edu
Date: Sat Jan 17 2004 - 08:17:20 PST 

Message-ID: <1780.209.239.173.234.1074356240.squirrel@www.exo.net>
Date: Sat, 17 Jan 2004 08:17:20 -0800 (PST)
Subject: Re: pinhole rising water level science
From: pauld@exploratorium.edu

Hi Treena

Have the student put a candle into an inverted jar with water partly
filling the jar. Light the candle with a magnifying glass and sunlight.

Observe what happens to the water.

The theory is that the air heats up pushing the water out, then cools when
the candle goes out drawing the air back in.

When the candle burns it uses up oxygen and produces CO2 and H@O. Both of
these gasses are much more soluble in water than gasses in air. So they
dissolve in the water leaving the gas state, lowering the presure in the
gas in the glass. The water is then pushed up into the jar.

Try the experiment using cooking oil instead of water and see what
happens. Water produced by the burning candle is not soluble in oil.

You can also replace the candle with wet steel wool. (Usually inside an
inverted test tube.
The steel wool removes the oxygen through rusting over several hours. The
water level rises without much temperature change. Because the oxygen gas
is removed to become part of a solid.

Paul Doherty

> I have a student who wishes to prove that when burning matches suspended
> on water in a closed glass (glass set on top as they burn), the rising
> watre level is due to the consumption of oxygen -- my understanding is
> that another gas is produced, effectively replacing any consumed O2, and
> that the rise in the water comes from a temperature difference -- First,
> is this understanding correct? Second, how do I channel this students
> energy? It's not enough to say, it is such and such gas replacing the O2
> ... can anyone think of a way to demonstrate that it is indeed due to
> gases occupying less space when cooled
>
>
> Treena Joiful
>
>
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