manganese is actually a much more
interesting metal than you might expect
I should say element perhaps than metal
so first thing I need to do is light the
bunson
so there we
are okay and then what we've got inside
the boiling tube is actually potassium
permanganate it is one of the transition
metals and the row of transition metals
stretches all the way from Scandium over
here to zinc over there what makes
manganese particularly interesting is
that it is in the middle of this
transition group there are 10 transition
metals from Scandium to zinc and
manganese is number five the reason
they're 10 is because each of them has a
certain number of D electrons one for
Scandium 10 for zinc so manganese in the
middle has five and
five if you're a mathematician you will
know is half 10 so it has exactly half
the number of Del electrons that can be
accommodated in the cell all I've gone
and done is just popped a couple of
spatulas of potassium permanganate into
the boiling tube and as you can see from
the color it's a very very dark almost
black uh possibly a dark green so that's
in there but let's begin just having a
look at the metal itself this is a
bottle of manganese is that Neil has
lent us and Brady promised that we
wouldn't break it and don't tell anyone
but I dropped it and a bit has fallen
out at the bottom look you broke it you
broke
it Neil's going to be very angry at
anyway let's look at the
metal so you can see the metal is in
this particular form is come in sheets
but has this rather
bobbly feature on the
surface this is the top of where the
metals and it's been broken up what is
also interesting that I've got a magnet
here and you can see it's not magnetic
at
all and
you can't pick it up now you can ask why
is it interesting if something's not
magnetic lots of things are not magnetic
and the reason that's interesting is if
you look at its salts so this is a salt
of manganese the label is not very good
but it's manganese sulfate MNS so4 the
first thing that you notice is that it
is almost white it's very slightly pink
and this is surprising because
especially in your um first chemistry
lessons they say the characteristic of
the salt of transition metals is that
they're colored and here's manganese
sulfate Almost White remember that
manganese metal is not magnetic let's
take the same magnet into the sulfate
push it down so you can see that the
salt sticks to the
magnet now I think that's
extraordinary normally you don't expect
salts to be magnetic and it's even more
surprising if the metal is not magnetic
but the salt is off the safety Flame
into the hot blue flame get so that it's
at the tip of the flame it's nice and
hot there ah you see that movement there
perfect that movement there oh you can
see it going right the way up the tube
and now it's dropping back down again
and what's happened there in the heat
we've changed the oxidation state of the
manganese to plus six so it's now K2
mn4 you're also getting oxygen which is
why you saw that movement of the powder
as the gas is being liberated it it shot
up the tube and you're getting manganese
dioxide
there and the reason why the salt is
magnetic is because it has five
electrons these five electrons in the
Dell and they're so-called unpaired
they're each in a different volume of
space around the atom so each of them
has a strong magnetic effect and with
all five of them it's really really
magnetic and the fact that it the
material has no color is also associated
with these five electrons if you drop a
solution of Manganese sulfate which is
also colorless into sodium hydroxide
solution you get a precipitate of
hydroxide and because there is air
dissolved in the sodium hydroxide the
oxygen removes one of the electrons from
the manganese so it now is so-called
manganese 3 which has only four
electrons and it's nice brown color so
you suddenly get this color
change this was one of the first
experiments I did in my second year at
University in a practical class they
didn't tell us what was happening we had
to explain it and so now we need to make
sure all of it is being converted to
plus six oxidation state so I'm going to
make sure it stays in that flame for
just that bit longer the really famous
compound of Manganese is potassium
permanganate which is a purple color
potassium permanganate is K M4 in fact
in the M4 minus the permanganate ion
manganese has no de electrons at all
they've all gone to the oxygen and this
very bright color is because the light
makes one of the electrons jump back to
the manganese
so you get this very intense color which
is very bright even a small amount of
the material causes a lot of color and
if you drop just a few tiny crystals of
permanganate into water you can see this
beautiful purple color spreading out I
persuaded Sam to repeat one of the
earliest experiments I did myself after
reading about it in a book heating
potassium permanganate
and so apart from that movement of the
powder up and down the tube it doesn't
look like anything else is really
happening I did this when I was 14 or 15
Sam is using a nice boiling tube I used
a metal spoon and a gas stove we're
going to put it into this uh scented
funnel that's set a top of the conle
flask and then I'm going to add some
concentrated alkaline to it and when you
heat the perangan it up there is a sort
of small puff of gas but nothing very
exciting but then you make so-called
potassium manganate K2
M4 which is bright green if you put it
in alkal
solution so
Sam if she's done what I suggested has
poured the solid out into a filter
and then poured over it some strong
alkal and you should see this really
nice dark green color solution coming
through and you can see there normally
if you put potassium manganate in
solution I.E just in water it' go a nice
purple color but here because you've got
K2
mn04 um it's actually giving you a
lovely green color but it's not a very
stable compound and if you add acid to
the solution it decomposes very
quickly and so you get permanganate back
again plus a precipitate which you may
or may not be able to see of Manganese
dioxide which is a brown solid now when
I did this experiment as a school boy in
the
kitchen I didn't know all of this
chemistry and my sister's clothes were
on the draining Board of the sink they
were being washed
and I'm ashamed to say and I didn't
notice that some of the permanganate or
manganate got onto my sister's
clothes and brown spots appeared all
over it and I was not very popular with
my parents what were you punished I
can't remember I think I was forgiven in
the interest of science
13,482 do you recognize that I feel like
I should you should that is the biggest
Brady number that appears in the first 1
million decimal places of Pi