so there's been a demonstration that's been on my to-do list for some time and
that's the chemiluminescence of singlet oxygen and I've always been kind of put
off from doing it because of not having a chlorine cylinder handy, seeing that
the actual sort of wash bottles that were often used in the traditional way of
showing this demonstration a little bit fancy maybe. I certainly didn't have it
immediately to hand in such a way that I could quickly and easily show it to some
students within school. And then I got thinking about whether or not I could
actually generate some chlorine gas in situ sort of the microscale and Bob Worley,
of course the king of microscale, very kindly pointed me in the direction of
Bruce Matson's microscale gas chemistry where my mind was blown as I realised
that actually getting myself some chlorine that I can use and show in front
of a class was as simple as this.
What I've just done there is in a matter of seconds generated about 60 ml of
chlorine gas that I can now just go and plug straight into a demonstration – no fuss. Let's find out how.
Okay so we're gonna be using an adapted version of a
technique that was published by Bruce Matson in his freely available microscale
gas chemistry book so I'm gonna actually leave the link for that it's
gonna be in the article. Of course the article is always on the Education in
Chemistry website and hopefully the RSC will be kind enough to add a little link
down in the description as well. When you have a look at this book your ideas are
gonna be going crazy. There's so much good chemistry that you can be doing
here with such simple equipment. A lot of people get put off by microscale
chemistry because they think that they have to get like really special fancy
stuff. I mean you can get like these syringe cap heads but just to try and
illustrate how simple this is I'm gonna be working with some wall tack today to
minimise as much as possible any sort of fancy special equipment. What do I have?
I've got a just a regular 60 ml disposable plastic syringe and I just
want to make sure that that's nice and freely moving. I've actually given this
one a little bit of vegetable oil around the outside of the plunger just to make
sure that that's actually moving nice and freely once it gets going so that
any gas that's generated doesn't require too much pressure to get that
plunger moving. What else have I got? The stand here obviously a conical flask
optional but kind of handy especially when I'm talking to video. What is
required is like a vial cap, essentially something that's going to
sit inside your syringe and that's going to contain one of your chemicals and you
can see how this actually fits nicely within the syringe here
and then actually I'm going to sort of add the acid into the vial cap and the
bleach for this reaction is going to be drawn into the syringe from the bottom. And so you need a vial cap
that's actually going to be able to still contain 1 ml of your acid and yet float. Okay, so something like this is
just like the again vial caps that I just found over in biology, didn't need
anything special for this to get going. Likewise you could, you need some kind of
a well to draw up some liquid from so I've got a dropping tile; you could also
use a weighing boat. It doesn't really matter the key thing is that you want to
be able to get the end of your syringe into the liquid and draw up as much
liquid as possible and as little air as possible when you do that. And for our
reaction today generating our chlorine there's more than one technique that you
can use for this, again, sort of links available as ever in the EIC article and
hopefully there'll be some links down below. Here we're going to be using some
5 M HCl and some fresh sodium hypochlorite bleach, really important
that you some decent fresh stuff. Obviously this won't work with peroxide
based bleaches either, so go out and get a fresh bottle if you want this
to work. In the article I mentioned 6 M HCl because that's what Bruce Matson
uses but a 5 M actually is perhaps more likely to be found around
the department and I find that that works pretty well as well. So I'm just
trying to show as much as possible what can be done with what was just sort of
able to be gathered from around the department without people getting sort
of freaked out that microscale chemistry needs some special kit or something like that.
Okay, so what I'm going to do is draw in 1 ml
of acid into my vial file cap head and then I'm going to actually pull into the
base of the syringe my bleach. And I'm going to need 3 ml of bleach and 1 ml of acid.
You want to get as close as possible to
that 3 ml of bleach because, of course, if you sort of go too far
either side you'll end up generating less chlorine.
Now Bruce Matson, incidentally, always has this technique about sort of filling up the syringe
with water and then with your thumb underneath or something like that and
then floating in the reactants on the to, because normally it's a powder and
then sort of letting your finger off and allowing the liquid to sort of run down.
In our case we don't need it, because actually we can load the acid straight
into the vial cap using a dropping pipette. Thanks to Peter Borrows from
CLEAPSS for actually pointing that out to me sometimes you can't see the wood for
the trees so that's what we're going to do today.
So at this point I just want to put a little cap on the end of my syringe.
So with the acid and the bleach in place and the cap on the last thing you need
to do a course in the fume cupboard is to flip over the syringe, give it a
little bit of a shake and potentially assist the plunger in moving backwards.
At this point you'll find that the syringe will basically be full of
chlorine gas and there's going to be some unreacted liquid that you want to
get rid of in there as well. Now to do so I've got a waste beaker with some 1 M
sodium hydroxide in it, but you've got to be careful, of course. There might
be a little bit of positive pressure in here from the chlorine so what I'm going
to do is, leaving the syringe facing upwards, pointing it away from my face,
I'm actually going to draw back a little bit on the plunger just to reduce some of
that pressure as I take the cap off and flip over, dropping out any of the excess
liquids into the waste beaker with a minimal loss of chlorine as I'm doing so.
So we've generated some chlorine in a syringe, what are we going to do with it?
Let's see if we can observe the chemiluminescence of singlet oxygen.
Now to do that, you can see here how I've got a clamp stand with a dummy tube of
chlorine that I've sort of got set up here. On the end of that there is 5-15 cm
of silicon tubing. It doesn't really matter too much. The key
thing is you've got that bend that you can generate to deliver a Pasteur
pipette into the base of a medium-sized test tube. And in the medium-sized test
tube I have some 100 vol peroxide. And just before I get going with the
demonstration I'm gonna add some 6 M sodium hydroxide, 5 ml here,
made by adding 1.2 g of sodium hydroxide to the water. The reason I'm
not going to add it immediately is that the alkaline peroxide can begin to
decompose so I really want to just sort of add that in when I'm ready to go.
So I'll connect up a genuine tube of chlorine gas here, add my sodium
hydroxide, dim the lights and we can see the chemiluminescence of singlet oxygen.
So I've lowered my syringe into the solution now, all I need to do is start squirting.
The key thing is to try and sort of pump in the chlorine in little
bursts, because you'll find that the bubbles that are generated in the
peroxide can cause it to get a bit cloudy and obscure the best of the red glow.
Let's have a look and see how we get on.
So there you have it, singlet oxygen chemiluminescence demonstrated in a
quick and easy reaction there with the help of Bruce Matson's fantastic microscale gas chemistry,
generating some chlorine in situ and you can believe it
won't be the last time we'll be exploring some of Bruce Matson's
beautiful in syringe, in situ gas generation techniques in this column in
the future, but for now give this one a go.