Due in part to it's simplicity and to the
crowd pleasing nature of the flame and woosh
that give the demonstration it's name,
the methanol woosh bottle has exploded in
popularity in chemistry class rooms in
the last ten years or so.
Exhibition Chemistry described this
demonstration back in September 2009.
This month we're going to be looking at a
variation that allows us to see how the
energy from the reaction
can be put to some good use.
So you're
going to need a one or a one and a half litre carbonated
PET drinks bottle, which is going to be our
rocket. Look out for the PET symbol on the bottom
or a number one inside the recycling
logo. You're also going to need about six ml of
ethanol and a metre ruler to
which you can attach a splint
and a section of guttering, which is going to act as a ramp
for us. Now we've attached some cardboard
to the bottom of this, but you can just
prop it up on some books,
about 20 degrees works just fine. We're
working with
ethanol here to avoid any of the
accidents that have recently been coming up
with methanol.
It's a little bit less volatile, it's
not absorbed through the skin
in the way that methanol is, so it's a
much safer alternative.
So before you start you're going to want to put a hole in the bottom of your bottle to act
as the exhaust,
about five millimetres. You can poke that
through with a braddle,
or what works really nicely is to get a
glass rod, hold it in a Bunsen flame
and then just pass it through the bottom
of the plastic while it's still hot.
Next thing you're going to want to do is to
hold your finger over the end of the
bottle and pour in the ethanol.
Lid back on the top.
Give it a good shake so you're coating up
all of the inner surfaces with the
ethanol and we're getting a
good fuel/air mixture
vapourised inside. Once you've given that
a good shake,
lid back off and pour out all of the excess
liquid. So you want to be drawing your
class's attention to the fact that
there is no liquid actually remaining
inside there.
It's only the ethanol vapours that we're
interested in and of course the oxygen.
Now before
performing a demonstration the first
thing you need to do is to dispose of
the
excess ethanol. That can be done down the sink with plenty of water.
Many of the accidents that are happening at
the moment with the methanol woosh bottle
are to do with the fact that a little bit too
much methanol is being used
and also potentially that the
excess methanol is being kept too close
to the demonstration while it's happening
so make sure you dispose of that. The bottle will last for a decent while before you
need to light it.
When ready to go, if you leave the bottle
at the bottom of the ramp,
protect audience and demonstrator with a safety screen and
light with the end of a splint and just let it go
