today we're going to show you acid rain
this used to be a huge environmental
problem we're going to demonstrate it to
you in the lab and we're going to do it
with a piece of kit which I inherited
from my late friend David Jones
we got the kit but not the instructions
but Neal worked out how to use it the
problem of acid rain is that in the
1960s 1970s people were burning fuel
particularly cold that contained a lot
of sulfur they were burning it in their
homes in power stations and even at one
time in trains in railway locomotives
and when those sulfur containing coal
burns it generates so2 which is a gas
and sometimes so3 which is a solid but
it's generated as fine particles in the
air and then when it rains these gas so2
and so3 dissolve in the water to give
either self euros or sulfuric acid acid
rain has caused huge environmental
problems particularly killing forests
because trees like pine trees and so on
normally do not grow on very acid soil
and we're talking about really quite
acidic rain on the east coast of the
United States some of the acid rain had
an acidity a pH between that of lemon
juice and battery acid so the experiment
consists of a large container in which
you can burn sulfur
to generate the so2 to so3 it then has a
vessel on top in which you can put water
in and the water is sprayed out of some
glass arms so you get rain going into
the gas the problem is of course you
can't see whether the water has become
acidic if you just use plain water so
you have to put in indicator
he added a tiny bit of potassium
hydroxide which made it nice blue color
and if he gives acidic to to turn gray
run number one Neal was unduly modest
put in just a little bit of sulfur
wasn't enough
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it rained but no acid so next time
Neil let himself go and put in a large
amount of sulfur
he burnt well in fact it caused fog
inside the container that's rather
interesting because when people burnt
coal with sulfur in it we used to get
terrible smaug's people couldn't see
their feet when they were bicycling
because the smoke was so thick
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the experiment then worked really nicely
you could see the water going down
forming raindrops and as the drops fell
they went from blue to red
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Brady was quite courageous he put his
camera in the water
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[Applause]
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you can see the raindrops coming down
and eventually it was drown but don't
worry
was okay
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we really like the demonstration and I
think the important thing to know about
acid rain is that it was a huge
environmental problem but it is one
which chemists and engineers have
succeeded in more or less solving
domestic fires these are heating in
houses now uses coal which has had the
sulphur removed and in large power
stations they take the flue gas that
comes out of the boilers and de sulfur
eyes it usually by reacting it with lime
the so2 reacts with the lime to make
calcium sulfate which is innocuous it
can just be put to landfill nowadays
most power stations certainly here in
the UK use natural gas methane rather
than coal so the amount of limestone
that is being used for desulphurization
is going down for a substantially but if
you went out for a stroll in that
romantic-looking mist hanging over the
trees around the lake the chances are
that you would be breathing in a dilute
form of sulfuric acid acid rain was not
a big issue here in the UK because most
of the so2 was injected quite high in
the atmosphere and blown over to
mainland Europe where there's much more
forest than in the UK tall chimneys
throw sulfur Laden exhaust high into the
air and it had really quite significant
effects and the forests in Germany and
northern Europe it comes from both
Eastern and Western Europe but due to
the prevailing winds maybe around 50
percent comes from Great Britain when I
first came to Nottingham on some days
you could taste the so2 in the air
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the removal of the so2
has had one quite strange effect that
Nottingham was famous for growing roses
and it turned out that the so2 in the
air was very good at killing the some of
the mildew and other pests that can grow
on roses so when the air was cleaned up
the roses started getting all of these
pests and now the rose growing industry
around Nottingham has more or less
disappeared would you like to learn more
about rain drops how about the shape of
raindrops our sister channel all about
physics sixty symbols has you covered on
that one also thank you to everyone who
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