Nigel's Close Encounters of the Elemental Kind

My good friend Susanne Hantos (MRACI) in Sydney drew my attention to the Royal Australian Chemistry Institute’s activities in celebration of the International Year of the Periodic Table. The RACI invites contributions relating to personal experiences with the elements https://www.raci.org.au/events-awards/stories-from-the-periodic-table. I am not associated with the RACI but I have had some nearly out-of-body experiences with certain members of the Periodic Table, and so I thought I might start a mini-series of posts about some of my Close Encounters of the Elemental Kind.

No. 1. The Trouble With Bromine.

At university I became very active with the student chemical society. At various times I was treasurer, secretary or chairman. Our chemical society was very much socially orientated and we employed a number of publicity stunts to promote our social events such as beer and skittle evenings, film nights and even Friday evening lectures by visiting chemistry glitterati.

Many of our publicity stunts took place in the Students’ Union building on campus. We had developed a kind of formulaic way of attracting attention. The standard display was a very large flask of water into which dry ice cubes were dropped. This of course generated the familiar bubbles and smoke effect. https://youtu.be/r2eU4vq-cd8

After a number of these same publicity stunts over several months I decided that the students, who we wanted to tempt to our social events, were fatigued with the dry-ice-in-water demos, and I resolved to try something more exciting.

Eureka! Oscillating Reaction! Chemical Clock! If you set things up correctly the Belusov-Zhabotinski (BZ) reaction https://youtu.be/g3JbDybzYqk will change colour: red-white-blue sequentially and repeat every 10 or 20 seconds or so over quite a long time.

Just The Thing for a new Chemical Society Publicity Stunt!

(A bit of chemistry coming up: (keep this for later on) the essential ingredients for BZ are sulfuric acid, malonic acid, sodium bromide, sodium bromate, redox (ferroin) indicator, and in our case - the special ingredient - an inert suspension of calcium carbonate).

To attract punters to our next social event we set up a BZ reaction - Big Time - outside the refectory in the Student’s Union just before lunch. We wanted to grab them as they went into lunch and as they came out.

“Big Time” meant a 50 litre flat-bottomed flask, full of the BZ reaction mixture which was very big and very heavy. At first all went well. The students were fascinated by the colour changes and it drew them to our demo, like flies to the honey pot, whereupon we separated them from their money to finance the next pub night.

The BZ reaction continues for quite a long time, but not for ever. By the time the refectory began to close and the last dregs of students were leaving, our BZ had slowed to a stagnant grey sludge.

But there were still gullible undergraduates around. With money! And we needed to extricate one from the other, to pay for the up-coming beer session. 

We needed to attract their attention. But how?

The BZ demo had dwindled into something that looked like waste water from a washing machine

We didn’t have the time to spare for the effort to set up a new BZ (it’s quite complicated).

What to do?

Inspiration came soon enough!

I decided to revert to the tried and trusted, but boring solid carbon dioxide.

I shot back to the chemistry department and filled an insulated bucket with dry ice.

I was back at the Students’ Union within a few minutes, most of the undergrads had finished lunch, but swarms of them, who wanted to skip afternoon lectures, had migrated to the coffee bar, which was by now, filled to capacity.

A captive audience! I rubbed my hands with glee. We were going to make a killing!

(And we (I) nearly did. Literally!)

Excitedly, I shovelled a good few dry ice pellets into the now-spent BZ mixture.

And this is where things started to go wrong. (There’s some more chemistry coming up now so pay attention).

BZ is a non-equilibrium oxidation-reduction reaction which alternates between an oxidised state and a reduced state.

So far so good.

The BZ blue colour is from the ferroin in a reduced state, the white colour is due to the calcium carbonate suspension special ingredient, and the red colour is from bromine in solution.

 The BZ eventually runs out of steam, and the equilibrium grey sludge is the result.

However, re energising the BZ mixture by shovelling dry ice into it, doesn’t re-set the chemical clock, Oh no!

What happens is the dry ice, stirs up the mixture and changes the pH - makes it more acid.

This has the drastic effect of liberating free bromine.

Lots of it!

In a confined space!

Bromine fumes are red and choking and dangerous, especially to chemical society members and lazy undergrads skiving off afternoon lectures in the student union coffee bar!

The atmosphere very quickly became unbreatheable and everyone in the vicinity started to cough, held their throats and fled the coffee bar with eyes watering.

Someone set off the fire alarms and the building evacuated. Distant sirens announced the imminent arrival of the emergency services and officialdom. There was going to be trouble.!

I wanted to get out before things got any worse. In the melée I had the presence of mind to try to remove as much evidence as possible. One of the miscreants made a rapid escape with the dry ice bucket and got away.

Meanwhile another culprit and I were left with the 50 litre flask which was still spewing choking red fumes.

“Quick! The gents!” I coughed to my only remaining perpetrator, intending to take the liquid evidence to the toilets and pour it away.

Not so easy! 50 litres of aqueous solution in a glass flask weighs more much more than 50 kg.

Nevertheless we did manage to manhandle the vessel - with its noxious content, sloshing about, and belching toxic fumes - as far as the men’s toilets without succumbing.

There my plan was to upend the flask and pour the contents into a urinal. Once empty we would do a runner with the flask, and we would be away, without a trace Apart from the poisonous vapours and scene of devastation left behind of course.

But it was not to be.

I had not reckoned with the special ingredient. The calcium carbonate was the source of the sludgy consistency, and at first it refused to leave the safety of its vitreous home.

After some vigorous shaking, the gunge was persuaded out of the flask where upon it proceeded to block up the urinal, and the liquid portion of the mixture overflowed on to the marble floor.

Remember that the liquid component contained sulfuric, malonic, and also carbonic acids, which reacted spectacularly with the tiles, fizzing and hissing as the marble disappeared.

And the only available neutralising basic substance was close at errr....hand.

We did a runner with the nearly empty glassware – a 50 litre flask is not something you can hide in your pocket -but we made our escape spluttering and choking without being apprehended by the campus security guards.

After a suitable period I believe the Students’ Union became habitable again, and a few days later I read a small headline in the students’ campus rag about an “Incident involving chemicals” in the undergraduate coffee bar.

No further action was taken and I retained my lofty position as an officer of the university chemical society

Later publicity stunts were based on liquid nitrogen demos (which involved different but less severe hazards. Depending on your point of view).

But that’s another story.