So chemical of the week this week is my one of favourite elements – Number 92 uranium. I have some personal experience with uranium as in a previous life I worked on a project for BNFL (British Nuclear Fuels Limited) so right away that tells you we are dealing with a radioactive gem. The 1789 discovery of uranium in pitchblende is credited to Martin Heinrich Klaproth, who named the new element after the planet Uranus. Of interest, uranium is the last naturally occurring element in the periodic table hence every element after uranium is referred to as a transuranic element. During her studies Marie Curie investigated the radiation emitted from uranium salts and discovered that the intensity of the rays was in direct proportion to the amount of uranium in the sample. She also found that pitchblende was much more radioactive than uranium itself, and realised that it must contain a new radioactive element subsequently named polonium.
Uranium has two isotopes: uranium-235 and uranium-238 (great element to introduce when studying isotopes in KS4) and it’s uranium-235 that’s radioactive. This means it’s a fissile material that will decay when bombarded with neutrons splitting and producing a lot of energy and more neutrons. Off course if the reaction isn’t controlled (the nuclear energy harnessed) what you get is a chain reaction causing a nuclear explosion. Uranium was the component of one of the atom bombs used in WWII. The bomb, ‘Little Boy’, was made up of pieces of uranium which when fired together by an explosive made a single piece of the correct size to go critical. There is an excellent article this month in BBC Focus magazine about the explosion in Hiroshima giving an insight into the immense devastation caused.
This always makes me think of uranium as a chemical story of two halves – not only does it have the internally locked power to destroy and annihilate but it also can be harnessed successfully to give us clean energy. To illustrate this, complete combustion (or fission) produces ~8 kWh of heat from 1 kg of coal, ~12 kWh from 1 kg of mineral oil and around 24,000,000 kWh from 1 kg of uranium-235 – that means uranium roughly contains 3 million times the amount of energy as coal. If only everything was straightforward, as although there is a huge energy potential with uranium, it must be mined and processed before it is used as a fuel. There is also the huge safety implications of running a nuclear power plant ( terrorist / natural disaster risk) and then what to do with the waste.
Uranium has a half life of 4.5 billion years so it is not going to decay any time soon. Disposal methods range from transmutation ( changing uranium to another element), dissolving the uranium in concentrated nitric acid to the most basic waste management technique for low level waste – burial. Unfortunately this means nuclear power is always going to be contentious issue. Uranium is an element of both hope and destruction. It has profoundly shaped the past, will hopefully change the future and will exist long after we are gone.
It was with sadness that I read that Oliver Sachs has terminal cancer. He wrote a very candid piece in the New York Times last week entitled ‘My Periodic Table’.
Oliver Sacks is Professor of Neurology in NYC School of Medicine and a noted author. So where does the Periodic Table link in ? Sacks has written a memoir called ‘Uncle Tungsten’ that details his childhood obsession with Chemistry. The joy of Sack’s writing is that he brings chemistry alive and he can see the Periodic Table as a living, breathing thing of beauty. Below are a few quotes from the book:
‘And I often dream of chemistry at night, dreams that conflate the past and the present, the grid of the periodic table transformed to the grid of Manhattan. […] Sometimes, too, I dream of the indecipherable language of tin (a confused memory, perhaps, of its plaintive “cry”). But my favorite dream is of going to the opera (I am Hafnium), sharing a box at the Met with the other heavy transition metals—my old and valued friends—Tantalum, Rhenium, Osmium, Iridium, Platinum, Gold, and Tungsten.’
I love the description of the transition metals as grey haired academics, with maybe Gold the Noble prize winner among them, meeting up for Opera. Sacks talks in his NY Times article about his friends celebrating his birthdays with elements and how he knows he will never see polonium (and how that may be a good thing!). That reminded me of a cake I had made for a fellow chemist recently, I’m sure Professor Sacks would approve !
This clever molecule is our weapon of choice against those airborne terrorists that seem determined to give us sleepless holiday nights plagued with swelling and scratching. Of course it is the dreaded mosquitos and thanks to research by the American army after WWII we have a molecule that offers some defence against their nasty bites. It should also be noted that in some parts of the world mosquitoes and other biting insects spread disease and cause widespread fatalities ( the WHO claim up to 1 million people die each year due to malaria). So it’s thanks to N,N-diethyl-3-methylbenzamide, also called DEET or diethyltoluamide, that we have a fighting chance.
Scientists are still not clear exactly how the molecule works – one school of thought is that the molecule interferes with the insect’s odorant receptors but it is looking most likely that mozzies just don’t like the smell. Products, such as sprays and creams, can contain DEET up to a concentration of 100% with the higher concentrations more effective for a longer periods of time. There is a lot of concern on the web about the safety of using DEET but if the recommended dosage is used and ingestion is avoided there are limited major health worries.
A quick look at DEET shows functional groups met at A2 level. This molecule would be a great starting point for some application questions eg. calculating molecular weight, reaction with bromine, acid/alkaline hydrolysis products …….
On a daytrip to Grasse I finally got to see perfume chemistry at work. We visited the Fragonard perfume house and had a tour of their laboratory and workshop. Fragonard is a family run perfume house founded in 1926 by Eugene Fuchs and the tour shows the development of the perfume making process from basic copper distillation tanks to modern glassware and analytical equipment.
What really stands out is the equipment used is recognisable to any KS3 chemistry student – there is fluted filter paper, distillation apparatus ( both old and new) and a separating funnel.
However, my favourite picture is of the desk used by the ‘nose’. To create a perfume, the perfumer will sit at this desk and go through the process of blending multiple perfume oils in an attempt to capture the desired smell specified in the brief for a new perfume.
Becoming a perfumer/ nose is a challenging process. Until recently, professional schools open to the public for training perfumers did not exist, and now there are only three prestigious institutions all based in France. The candidates must endure a demanding entrance examination and must have taken university-level courses in organic chemistry.
So how long could I blog before I mentioned the chemical composition that is – THERMITE – now that’s got your attention ! Described on wikipedia as a pyrotechnic composition of metal powder fuel and metal oxide but that really does not do it justice. Well what does then ? It has to be the Brainiac clips dedicated to blowing up a French car…
For the older readers look no further than Breaking Bad. One of my favourite scenes is when Walt and Jessie use the thermite reaction to create an explosion in order to open a methylamine store. Now, using filings from an etch-a-sketch as the reactants may just be a chemical step to far !
So how can we squeeze this little cracker into a scheme of work – for me it works best in KS3 introduction to Redox. The thermite reaction (it can have different components) of aluminium and iron oxide is the perfect example of a redox reaction – the iron oxide loses oxygen whilst the aluminium gains it. It does need an ignition and magnesium or potassium permanganate/glycerol can be used. The highly exothermic nature of the reaction and the high activation energy are good AS discussion points.
The thermite reaction was discovered in 1893 by Goldschmidt and its first commercial application was in 1899 when it was used to produce molten iron to weld tram tracks in 1899. But my favourite use has to be within the military where it is used in the emergency destruction of cryptographic equipment when there is a danger it might be captured by enemy troops – there’s one for the next James Bond movie.
I’m a big fan of the Royal Society of Chemistry (RSC) website and I’m hoping that beginning to write this blog will give me the opportunity to keep up to date with what’s happening outside the classroom in the big bad chemical world. There has been a lot of response recently to the RSC research into the public’s opinion to chemistry. I’ve really liked the recent opinion pieces by David Philips and Marc Lorch about this research.
The research has found that public opinion to chemistry was maybe not just as bad as expected but a picture of neutrality was found. The word ‘neutrality’ makes me sad. As teachers we are responsible for positioning chemistry within our pupils lives and an easy place to start is defining what a chemical is. Chemicals are bad, isn’t that right? They pollute, are toxic and of course have you heard of that really bad one known as dihydrogen monoxide? (….water). Marc Lorch mentions the term chemophobia but the actual research actually indicates that 60% of the public actually know that all things are made of chemicals. This got me thinking – Chemistry is not compulsory at GCSE so really as teachers we do not have much time to impress its importance. We need to start selling the periodic table, it’s our world’s Lego box and guess what – everything around us comes from those 118 elements ( let’s debate that number at a later date) and their combinations so if there is so much good and beauty in our world then thank you Chemistry ! What was great in the article was that David said chemists are passionate and we need to embrace a more strategic and contextual approach of public communication – and I think that has to start in the classroom.
I am a fan of Twitter and the New Scientist tweets pop up now and again. Recently I found this one interesting and no it wasn’t because of the Take That lyrics it was that it is about a catalyst. Sometimes I love nothing better than trawling the Internet to find out as much info as possible about something chemically related. Now, I can record what I find in this blog which will be great for teaching as every year I always say at some stage ‘there was this thing I read about … I must find it for next class’ and spend wasted time re trawling !
Anyway back to carbonic anhydrase – this stood out for me as i figured it must be something to do with the carbonic acid- bicarbonate buffering system that is studied at A2 .
These reactions are of great importance maintaining the acid -base balance in different tissues including the stomach and pancreas. This process is extremely important in all living animals. Carbonic anhydrase turns out to be the enzyme that catalyses the hydration of carbon dioxide and the dehydration of bicarbonate. So what actually is it – it’s a single polypeptide chain ( mw ~30,000) complexed to an atom of zinc and boy does this catalyst work – a million reactions per second. How does it work – now this is the interesting bit chemically. I’m going to try and explain in the most basic terms – a water molecule binds around the zinc coenzyme causing polarisation of the O-H bond weakening it. A histidine amino acid accepts a proton leaving a hydroxide ion ( ie water split up into ions) and the active site brings the hydroxide and carbon dioxide close enough to form bicarbonate. How clever is that little enzyme ! Now the good thing is that this biological workhorse has been recognised and there even was the 10th international carbonic anhydrase conference held in Holland this year. Also just read that modified carbonic anhydrase enzymes have been used in CCS, it just gets better ! Now go on I know you want to google CCS !