Category Archives: Fascinating chemicals

Decarbonation of Soda Water

My Year 12 Chemistry class were working on this *exciting* prac this afternoon, as part of developing their understanding of the equilibrium that occurs in the dissolution of carbon dioxide in water.

In the past, I have done this experiment as you might expect – take a small can of soft drink, crack the lid and let it sit for a few days alongside a control containing the same mass of water. You measure the mass of the cans before and after and calculate the mass lost due to CO2 loss. The control can helps to account for any evaporation, which tends to be most of the loss anyway. Not very exciting and not a lot of CO2 lost.

This time around I tried the salting out method, where you add 1-2 g of salt for every 50 mL of soda water. This causes the CO2 to effervesce immediately, leading to a totally flat bottle in about 10 minutes instead of days. Here are some sample photos:

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20140522-165027-60627749.jpgAs you can see, some groups added some universal indicator to see if there was any colour change. The fizz at the top was distinctly yellow-orange, but interestingly the rest of the bottle stayed the same colour. A far more effective method – definitely a keeper!

Fascinating chemicals – arsenic

This week’s fascinating chemical is arsenic (but we’re neglecting old lace for the time being – boom-tish!).

In what would most likely be the most obvious statement of the day, arsenic is a poison.  Because it was so frequently used by would-be rulers to murder their rivals in medieval times, it has been called both the Poison of Kings and the King of Poisons.  The use of arsenic for murder became much less effective, however, after a British chemist named James Marsh developed a test in 1836 that could accurately detect the presence and quantity of arsenic in a tissue sample.  In fact, this was actually the first documented use of forensic toxicology in a criminal case!

Historically, arsenic has also many other, non-murderous uses, including cosmetics, in Emerald Green pigment and as a food colouring for sweets in the 1800’s.  The toxicity of arsenic was one of the reasons that it was used in flypaper and rat baits and also for treating wood, until we came up with synthetic pesticides in more recent times.  Naturally, its toxicity towards humans meant that the use of arsenic has been almost completely banned.  However, a particular arsenic compound called roxarsone is still being used in chickens to prevent disease! I doubt that the levels are anything to worry about but it was a bit of a surprise.

The way that arsenic causes its lethal effects is highly complicated, but essentially it disrupts the internal energy systems of the cell, causing the cells to eventually die off.  Some of the symptoms of arsenic poisoning include headaches, nausea, diarrhoea, vomiting, painful convulsions and cramps, dehydration and weakness.  One reason why arsenic was considered to be such an effective poison is because several of these symptoms would also occur in someone suffering from cholera, so until the Marsh test was developed arsenic poisoning could more or less go undetected.  A more characteristic symptom that can point to chronic arsenic poisoning is the presence of horizontal white lines on the fingernail called Mees’ lines.

So a fascinating poison with a long history – keep the suggestions coming!

Fascinating chemical of the week – ETFE

This week’s fascinating chemical is (poly) ethylene tetrafluoroethylene (ETFE).  ETFE is a type of polymer (which in this case refers to plastics) that is closely related to two other, well-known polymers: polytetrafluorethylene (PTFE), better known as Teflon, and polyethylene (PE), which is used in everything from plastic bags to pipes.  Polymers are very long molecules with a chain-like structure made up of many links called monomers.  ETFE is related to these other two plastics because its chain consists of an alternating pattern of the monomers used to make both PTFE and PE.

ETFE was originally developed by DuPont in the 1970’s for use as insulation material in the aerospace industry.  However, the fascinating thing about this polymer is that unlike many other plastics it has great applications for architecture and building.  It is 1% of the weight of glass but it transmits more light, is cheaper to install and is much sturdier and more flexible.  Oddly enough for a construction material, it can be used in two different forms: the more conventional sheets of compressed plastic, or it can be made into pneumatic ‘cushions’.  The beauty of this cushion form is that it is possible to alter the properties of the material by adjusting the volume of air inside the cushion, in order to let in more light or create more shade.  It is also very versatile in that large sheets of ETFE can be sewn together to cover a very large area.  Naturally, when in this cushion form it is vulnerable to punctures so it tends to be mostly used in roofing.  It also poses extra challenges in terms of acoustics, as the cushions can act like a drum, amplifying the sound of rain.

There are several well-known buildings that have used ETFE in their construction, including the Allianz Arena in Munich (constructed for the 2006 World Cup), the Beijing National Stadium (known as the Bird’s Nest) and the Beijing National Aquatic Centre (known as the Beijing Water Cube), which is the world’s largest structure made of ETFE.  As you can see, the effects of using ETFE are very striking and represent an incredible leap forward.

If you’re interested, I got most of my information from here.

Fascinating chemical of the week – Hydrofluoric acid

Following on from the awesome science videos series of blog posts that I’ve started doing, I’ve also decided to create a series looking at new and fascinating substances that you may have never heard of before.  They may be dangerous, quirky, unpredictable or just have a really interesting history, but there are so many different substances out there .  To get the ball rolling, we’re starting off by looking at hydrofluoric acid (also know as HF).

Chemically speaking, hydrofluoric acid is similar to the more familiar hydrochloric acid – except it’s a whole lot more dangerous!  Highly corrosive, HF causes exceptionally vicious burns and extensive tissue damage, as it passes into the tissues much more easily than most acids.  To make matters worse, HF burns are often initially painless as HF readily destroys nerve tissue, so accidental exposures can go unnoticed until the damage is well and truly done.  It causes so much of its damage by removing calcium ions in the tissue (which are vital to muscle and nerve function), combined with a massive increase of fluoride ions in the bloodstream.

The corrosive nature of HF explains several of its common uses, as it is a part of some strong cleaning solutions.  In fact, it is so corrosive that it is one of the very few acids that can successfully etch glass, although bizarrely there are some plastics that are resistant to its damage.  It is also used to add fluorine atoms into hydrocarbon molecules for research, but it’s so dangerous that all the safety advice says to avoid it if at all possible.  So it may be useful, but I sincerely hope that I never have to use it!