Chemical of the Week 10 – Hydrogen Sulfide

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This week’s molecule came about because of an interesting conversation at a BBQ (thanks Gareth !). Hydrogen sulfide has been in the news recently as it can act as a superconductor at approximately 200K (-70 oC). Superconductors conduct electricity with zero resistance and also expel magnetic fields (Meissner effect) below a critical temperature. The ultimate goal would be to have a superconductor operating at room temperature resulting in huge efficiency savings when generating electricity. It seems that under high pressure (about 100 million times atmospheric pressure, created by pushing two diamond bits together) the H2S solidifies and is converted into H3S. The presence of hydrogen atoms in the compound is beneficial as hydrogen oscillates at the highest frequency of any atom. The researchers are now turning to other hydrogen rich molecules to try and increase the operating temperature even more.

Hydrogen sulfide is a colourless gas at room temperature but definitely not odourless. It’s the smell we love to hate, the smell of the stink bomb, rotten eggs. Sulfur and sulfur oxides don’t have a specific smell but reduce sulfur and all that changes. Organic molecules containing sulfur are renowned for being smelly. There is a great poster by compound interest showing all the smelly sulfur containing body odours.

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Hydrogen sulfide has to be handled with care as exposure to high concentrations of the gas can be fatal and it has been reported in some clusters of suicides. The town of Rotorua in New Zealand is famed for its geothermal hot springs and the associated rotten egg smell. As its population has had a low level exposure to hydrogen sulfide the World Health Organisation has issued a study on long term health effects of exposure.

Hydrogen sulfide is an important chemical on the AS syllabus, as we meet the group VI hydrides when discussing hydrogen bonding, we look at the shape of the hydrogen sulfide molecule (an analogue to the water molecule) and it’s also an example of the various oxidation states we can find sulfur in. It may not be as interesting as water but I think it gives it a run for its money !

p.s who grew up with hydrogen sulphide ?

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Pencil Cases at the Ready !

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As the holidays draw to a close there is the usual anticipation about the return to school – in the back of my mind there is always the amount of homeworks that I will have to set (never mind mark), the assessments, parents evenings, oh new course to teach and the list goes on. But this year I feel slightly different, and that’s due to the journey I’ve started both with the blog and Twitter. The blog has helped me archive all my chemistry facts and thoughts and it’s also made me work. (I did spend a whole afternoon recapping on D/L nomenclature for the L-ascorbic acid post!).

But the real discovery has been Twitter – by actively following chemistry and education accounts, I have started to feel really connected. In particular I have loved @compoundchem (finally able to read the fantastic compound interest posters) and @teachertoolkit, (loved the ripple effect). What has also really impressed me is Twitter has allowed me to follow what’s going on closer to home and in particular #niedcamp. It was the first teacher led professional development day -yes these teachers actually took a day out of their holidays to organise it .  I attended an excellent presentation from Dr Stephanie Nelson about the amazing resources the RSC have been developing (and I also got to meet @liviasmith21 aka science muppet – another passionate chemistry teacher). I’m hoping to trial some of the resources Stephanie showed us throughout the year and I will report back on the blog.

A big thank-you to the organisers of niedcamp for an inspiring start to the academic year. I love the following quote by William Butler Yeats – ‘Education is not the filling of a pail, but the lighting of a fire’ and I think it applies to teachers just as much as students !

Ps Check out this video clip I watched recently, if ever there was confirmation that chemistry is the subject to teach …..

Chemical of the Week 9 – Toluene Diisocyanate

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The news reports last week of the major chemical explosions in Tianjin, a major port in China, were very worrying. Current reports put the death toll at over 100 with massive devastation of the port area. It is thought the first explosion had a power equivalent to three tonnes of TNT detonating, whilst the second was the equivalent of 21 tonnes, the power was so great some thought it was a nuclear explosion. One of the chemicals being stored at the facility where the explosions occurred was toluene diisocyanate (IUPAC name is 2,4-diisocyanato-1-methyl-benzene). It is primarily used as a chemical intermediate in the production of polyurethane products, of which 11.7 million tonnes are produced annually. The global market for toluene diisocyanate was $ 6195.6 million in 2014. The worry is that toluene diisocyanate is extremely toxic from both acute and chronic exposures. Acute exposure to high levels of the chemical results in severe irritation of the skin and eyes and affects the respiratory, gastrointestinal, and central nervous systems. This explosion highlights the safety issues that surround the transport and storage of chemicals involved in major processes.

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Polyurethane is an interesting polymer as it can be tailored to be either flexible or rigid and is found in everything from car seats and mattresses to insulation foam. It is a condensation polymer made using the following difunctional monomers :- a diol and a diisocyanate. They react to produce a urethane linkage and any functionality found between the functional groups can dictate what type of properties the polyurethane has (for example hydroxyl groups can lead to cross linking of the chains which increases the rigidity of the polymer).

https://pubs.acs.org/cen/whatstuff/84/8402foam.html

Condensation polymers are on the A2 syllabus and I know that pupils do find the application questions based on these challenging (as soon as I saw this reaction all I could think was, ‘there’s a neat little application question’). Not only is the production of the polymer interesting but the production of toluene diisocyanate is very relevant as well. The starting material is methylbenzene which is nitrated, reduced (two reactions that are met at detail at A2) and then reacted with phosgene.

This blast has shone a light onto the importance of safety within the Chinese chemical industry. Questions have been asked as to why more than one dangerous chemical was been stored at the same site and the hope is that lessons will be learned from this tragic event to prevent it ever happening again. So as we lie on our memory foam mattress tonight it’s important to remember that the great benefits we gain from the chemical industry must be aligned with a responsible and safe approach to chemical production where safety comes before profit.

How Do You Like Your Periodic Table ?

One thing about being a chemistry teacher is that you get to look at the periodic table every day (well unless you have the misfortune to have to move about and end up teaching in a biology or physics lab…) . Sometimes I wonder is this why I’m so passionate about the periodic table.  Most chemists have a copy tucked away somewhere, usually at the front or back of a reference book, but for a chemistry teacher it’s the beating heart of our classroom. As I say probably at least once a day it’s the Lego of the world, our own set of building blocks. My classroom copy is from 1987 and believe me that doesn’t annoy me at all, in fact I love the fact that some of the transuranics have yet to be named. They appear as symbols Unq (104) Unp (105) and Unh (106). IUPAC, the organisation in charge of naming, used these as temporary names until suitable names were found (found this site that explains the naming http://www.periodni.com/naming_of_new_elements.html ).  Therein lies just some of the many dramas hidden behind the symbols. I love the fact that after the Cold War the Americans and Russians divided out the naming those elements between themselves – can you work out who got what!

So I thought I would leave you with a few different periodic tables to ponder over, first up is one that appeared on Twitter recently by @JamieBGall showing the different countries of discovery for each element.

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Next up, here’s one I made earlier – quite literally! During the week before Christmas 2013 I embarked on an ambitious project with my pupils to make a Hama bead periodic table. It was my own Field of Dreams moment – if you build it they will come!  A quick trip to Ikea,  a handful of enthusiastic pupils,  a dedicated technician and 33,000 beads later I don’t think we did too badly.

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And finally – ever wondered what to buy your chemistry teacher for Christmas ? Well this is it – it’s a real periodic table (well coffee table) with samples of many of the elements. Definitely my first purchase when I win the lottery.

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Over to you now, has anyone spotted any other periodic tables they want to share !

Chemical of the Week 8 – L-Ascorbic Acid

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Most parents have spent an appreciable amount of time trying to get their little angels to eat some fruit or veg. At the back of their minds, lingering behind the five a day, is the dread that their child could be the first in their nursery to have scurvy! Oh the shame! An extreme lack of vitamin C for long periods of time can cause scurvy. Symptoms of scurvy include skin that bruises easily, bleeding gums, joint pain and poor wound healing and if untreated can be fatal. Enter the molecule (R)-3,4-dihydroxy-5-((S)-1,2-dihydroxyethyl)furan-2(5H)-one – enough of this chemical and their little protégées will be well on the road to health and success!

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IUPAC, the organisation that names chemicals, definitely had their work cut out with that name, have you guessed what it is yet? It is vitamin C – which incidentally is more frequently referred to as L-ascorbic acid by scientists. L-Ascorbic acid is actually derived from Latin to mean ‘no scurvy’ and don’t ignore the L. The D/L prefix (although outdated) infers that this molecule has chirality. The D molecule is not found in nature and does not have any significant physiological activity. The beady eyed reader may have noticed that ascorbic acid actually has two chiral centres which results in two sets of enantiomers in total. If you look back to the IUPAC name the letters R and S indicate the arrangement of the prioritised atoms/groups around each chiral centre (R right and S left). Vitamin C (L-ascorbic acid) is very important because it is used in the production of collagen which is essential for binding cells together. Chemically, ascorbic acid has two ionisable hydroxyl groups and at physiological pH it exists as the ascorbate mono-anion. This ion can undergo two one electron oxidations making it a very good reducing agent and also an effective antioxidant.

Over a hundred thousand tons of L-ascorbic acid are produced annually worldwide, and the market price is less than a penny a gram. Vitamin C was first isolated in 1928 and by 1936 a process devised by the chemist Tadeus Reichstein, using D-glucose as a starting material, resulted in industrial production. The recommended dose for vitamin C is approximately 50mg a day, and you can reach that target by a healthy diet or supplement it with tablets. If you eat a camu camu or kakadu plum you will hit your target no problem, with more common fruits such as oranges and lemons having on average about 50mg per 100g (red peppers and blackcurrants are your best bet if you are looking for your vitamin C hit in the fruit and veg isle in Tesco’s!). Vitamin C can’t be stored in the body so daily ingestion is required and don’t worry about an overdose because vitamin C is water soluble. Interestingly it’s not just humans who don’t produce vitamin C, looks like we have more in common with guinea pigs than you would think! We both don’t have L-gulonolactone oxidase (GLO), the enzyme required for the last step in ascorbate synthesis, making our dietary intake vital (and therefore a vitamin).

Famous Chemists – Linus Pauling

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I mentioned Linus Pauling in my first post so I think it’s only fair that I give him the honour of a full post – being the only person to have both an unshared Nobel Prize for Chemistry (1954) and one for Peace (1962). Pauling is most famous for his work on the nature of the chemical bond where he used quantum physics to explain molecular architecture. His 1939 book ‘The Nature of the Chemical Bond’ remains the most-frequently cited book in the scientific literature of the twentieth century.  But what I love most about Pauling is the breadth of his studies – he was involved in the development of synthetic blood, identifying sickle cell anaemia as a molecular disease, developing an oxygen detector that could be used in submarines and of course in later life there was his interest in the uses for Vitamin C.

How did Pauling become such a noted peace activist ? This is very topical with the 70th anniversary of the dropping of the atomic bombs on Hiroshima and Nagasaki just last week. Pauling had declined to work with Robert Oppenheimer on the Manhattan project and the use of the atomic bomb near the end of the war was the catalyst for Pauling’s dedication to peace activism. From the late forties on, Pauling was a member of Einstein’s Emergency Committee of Atomic Scientists. During the McCarthy era, he encountered accusations of being pro-Soviet or Communist, allegations which he categorically denied. In 1958 he presented to the UN the celebrated petition signed by 9,235 scientists from many countries in the world protesting further nuclear testing and in the same year published his book No More War!. When the Soviet Union announced a resumption of nuclear testing in August, 1961, Pauling redoubled his efforts to convince the Russian, American, and British leaders of the necessity of a test ban treaty. His position is summarised in a communication published in Harper’s Magazine in 1963- ‘ I have said that my ethical principles have caused me to reach the conclusion that the evil of war should be abolished; but my conclusion that war must be abolished if the human race is to survive is based not on ethical principles but on my thorough and careful analysis, in relation to international affairs, of the facts about the changes that have taken place in the world during recent years, especially with respect to the nature of war.’
From the late sixties Pauling began a crusade to encourage the use of vitamin C for everything from living longer, curing the common cold and cancer. In 1970, Pauling published ‘Vitamin C and the Common Cold’ urging a daily dose of 3,000 milligrams of vitamin C every day (about 50 times the recommended daily dose). Unfortunately Pauling’s zeal for vitamin C’s efficacy did not stand up to scientific scrutiny and this has somewhat tainted his legacy. I’ve added a link to a site that discusses the most recent research in this field.

https://www.sciencebasedmedicine.org/high-dose-vitamin-c-and-cancer-has-linus-pauling-been-vindicated/

However, Linus Pauling had a lot to teach us as he showed us both the moral fibre of science and the depth and breadth of the scientific mind. Interestingly Einstein made the following comment about Pauling ‘Ah, that man is a real genius!’  If you want to find out more about him there is a great website at his alma mater Oregon State University.

http://scarc.library.oregonstate.edu/digitalresources/pauling/

Chemical of the Week 7 – Graphene

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It harder than diamond, a better electrical conductor than copper and stronger than steel – it can only be the Nobel winning material Graphene. I thought this current material ties in well with the last post on chemical structures.  The great thing about graphene is that as it is a single layer of graphite most GCSE students are able to draw the structure and explain its properties. Graphene is a 2D hexagonal lattice of carbon atoms and its large scale delocalised electron system make it very stable. It was discovered in Manchester in 2004 by Professors Geim and Novoselov and they were awarded the Nobel prize for the material in 2010.

Graphene has come a long way from its breakout in 2010 and the UK government has invested £50 million in the Graphene Institute. The idea is to take this material all the way from lab to the shop floor and position the UK once again as a technological leader. Although Geim and Novoselov created Graphene by using sticky tape to peel a single layer from a sample of graphite, making large amounts of this material is not straight forward. Applications of graphene are wide ranging from replacing rare or less efficient materials in electronics to transparent cabin wall membranes in airplanes that allow passengers panoramic views.

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But what’s current with Graphene – it’s Kirigami. Kirigami is a variation of origami in which the artist cuts paper to transform a two-dimensional sheet into three-dimensional structure. Paper will tear when stretched but if cut it becomes more flexible – remember all the paper snowflakes you made during the week before Christmas at school !  A stretchable and bendable transistor has been made by researchers in the US by applying the principles of Kirigami to graphene. I think this just illustrates the beauty inherent in chemistry – the marriage of an ancient Japanese art with a recently discovered ground breaking material leading to a cutting edge technological development.

But move over Graphene – hot of the press, the current edition of Nature has an article about graphene’s cousin Stanene. Stanene is a 2D material made of tin ( instead of carbon) and is described as a topological insulator. This means electrons can’t travel in the bulk of the material but can along the edges and topological insulators are the one sure thing to get physicists excited these days. I’m not even going to begin to explain how a topological insulator works ( ie don’t really understand it ) but I found this really interesting blog post which I was just about able to follow !

http://scienceblogs.com/principles/2010/07/20/whats-a-topological-insulator/

I’ll leave you with a quote from Wolfgang Pauli – ‘God made the bulk; surfaces were invented by the devil.’