Basic Chemistry

basic

The other end of the pH scale.

When you start writing a blog it’s hard to predict what people will find most interesting. Inevitably, it’s not what you expected. For example, two of The Chronicle Flask’s most-read posts are about rhubarb and lemons. Perhaps people are more interested in fruit than I ever imagined. Or perhaps I’m getting a lot of hits from people mistakenly looking for recipes.

Or maybe it’s because both feature the ever-interesting topic of acids. In which case, I should probably write something else about acids.

So, this is a post about bases.

Just in case this spectacular bit of contrariness isn’t immediately obvious, bases – some of which are called alkalis (I’m coming to that in a minute) – are at the other end of the pH scale to acids. Acids are the things with a pH value of less than 7, and bases have pH values of more than 7. So basically (hoho), they’re the opposites of acids.

whysoblueI’m using the word base deliberately, and not just because of all the brilliant chemistry puns you can make with it. The more familiar word is probably alkali, but while all alkalis are bases, not all bases are alkalis.

Alkalis are often described as soluble bases. More precisely, alkalis are produced from the metals in group 1 (the ‘alkali’ metals) and group 2 (the ‘alkaline earth’ metals) of the periodic table. The more general term, base, applies to anything that can neutralise an acid. Chemists have another definition: a base is a proton (H+ ion) acceptor, while acids are proton donors (actually chemists have yet another definition, but the proton acceptor one is the one that gets trotted out most often).

The distinction between alkalis and bases does matter to chemists and the two types of substance usually look quite different – bases tend to come in solid lumps or powders (baking soda, for example) and alkalis are more likely to arrive as a solution in a bottle – but in terms of chemistry they both get involved in the same type of chemical reaction, which is neutralising acids.

Indigestion tablet advertWe make use of this all the time, whether we realise it or not. For example if you’re suffering from acid indigestion you probably reach for the indigestion tablets. An advertising campaign for a particular brand of these says that they “turn excess acid into water and other natural substances”. Those ‘natural substances’ are salts – presumably it was decided that the word ‘salt’ had too many negative connotations (which is probably true: how many people would pop a pill that promised to turn into salt in their tummy?) The main ingredient in the tablets in question is calcium carbonate; a base that reacts with stomach acid to produce calcium chloride. Which is definitely a salt, if not the one most people think of when they hear the word.

Tangentially, calcium chloride is also a food additive with the E number E509. It falls into the category of anti-caking agents, which is sort of funny when you think about it.

Anyhoo, that’s one place you use a base (rhyming now as well as punning, sorry). You’re actually making one yourself every time you eat, because your liver produces a substance called bile (bloggers love bile) which helpfully neutralises the acid your stomach produces. If it didn’t, your intestines would get damaged by that acid, so it’s important stuff.

Interestingly, in a lot of the older medical traditions (you know, swallow three leeches with meals, turn around three times under a full moon and bury a toad under a horseradish in a mock turtle) the body’s health depended on the balance of four ‘humors’, or vital fluids: blood, phlegm, ‘yellow bile‘ (choler), and ‘black bile‘. If you had too much of the last two, it was supposed to cause aggression and depression, and in fact the Greek names for them are the root of the words cholera and melancholia.

It’s interesting that in the 21st century many people are obsessed with ‘alkalinizing‘ the body (just check out the comments on that lemons post) when for thousands of years people have understood that too much alkali is probably a bad thing. Public understanding of science has really moved on hasn’t it?

soapBile does something else that’s really quite important in the body, it helps you to digest fats. Bases are generally really good at breaking down fats. This is another thing that’s been known for quite a while, ever since soap was first discovered about (sources vary quite considerably on this) six thousand years ago. Soap is made by a process of saponification, in which fats react with a strong base, usually sodium hydroxide (otherwise known as caustic soda, or sometimes lye). This breaks apart the fat molecules to make glycerol and carboxylate salts (they’re the soap bit). Because of this use, sodium hydroxide features in a famous, and rather gruesome scene, in the film Fight Club.

firediamondNaOH

The fire diamond for NaOH

Because bases are so good at breaking down fats they’re actually surprisingly (or not, if you’ve just watched that Fight Club clip)dangerous, especially because they’re also quite good at breaking down proteins. Your skin is mostly fat and protein, so they can do quite a bit of damage. Remember fire diamonds? The one for sodium hydroxide has a 3 in the blue box, which means that short exposure could cause ‘serious temporary’ or ‘moderate residual’ injury – yikes.

Corrosive hazard symbol

Corrosive hazard symbol

The European hazard symbol is even more alarming, featuring a hand with holes being burned through it. Of course, acids have symbols like these too, but people sort of expect acids to do this kind of stuff. Whereas they’re often (unless they’re chemists) strangely unaware of the dangers of alkalis. For example there’s the a famous, and gruesome, story of the serial killer John George Haigh, who famously dissolved the bodies of his victims in oil drums full of concentrated sulfuric acid. It worked quite well, but he was caught eventually when the police searched his workshop and found sludge containing three human gallstones and part of a denture.

Sulfuric acid is a particularly powerful acid, and is undoubtedly incredibly dangerous stuff, but sodium hydroxide is not much safer. It will cause instantaneous and serious burns, and solid sodium hydroxide gets incredibly hot if it’s added to water. In fact, the water will quickly boil if you’re not careful.

In May last year American Carmen Blandin Tarleton was in the news because she had just received a face transplant. She needed it because her estranged husband had doused her with concentrated sodium hydroxide six years previously. She had undergone fifty-five operations before she made the decision to get the transplant. The pictures are really quite horrific. I won’t reproduce one here; you can see the result of the attack if you follow the link above. Tarleton has also written a book about her experiences. She was left blind and horribly disfigured, with burns to 80% of her body. Doctors described it as “the most horrific injury a human being could suffer”. Sodium hydroxide is not nice stuff.

It’s surprisingly, shockingly, easy to buy sodium hydroxide. Because it’s used in soap-making, you can get it quite easily. It’s even available on Amazon. And of course it’s an ingredient in lots of drain cleaners available in supermarkets. When they say you should wear gloves to handle this stuff, it’s definitely not health and safety gone mad. You really should. Even I would (and I’m really bad about wearing gloves).

So spare a thought for bases. They’re just as interesting, and certainly no nicer or safer than their acidic cousins. In fact, they’re so good at breaking down fat and protein that they could arguably be more dangerous. And next time you’re cleaning out your oven, do remember to wear your gloves.

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Baffling gases

The benefits of nitrogen tyre inflationToday I had to pay a scary amount of money for new car tyres. And, in yet more evidence that chemistry permeates everywhere, I found this amazing sign in the garage.

I studied it at some length. The diagram on the right particularly fascinated me. They’ve helpfully included a key, which seems to suggest that the peculiarly square-shaped ‘tyre’, labelled as being filled with compressed air, only contains particles of nitrogen vs compressed air signoxygen, water (and water vapour, because ‘water’ isn’t a broad enough label apparently). The other, nitrogen-filled, one appears to contain oxygen, water (and water vapour) and nitrogen. As well as some mysterious green and red circling arrows.

Hm.

I can’t quite get my head around it. Someone drew this, and sent it to printers, and presumably it’s been displayed in more than one reception area (I’m deliberately not naming the specific garage, since the staff there were nice and helpful and gave me a good price really, and I’m sure they had nothing whatsoever to do with the sign beyond being told by Head Office to put it on the wall).

Did no one think to check it with, well, anyone? It’s almost as bonkers wrong as the American school sign advertising ‘leteracy night’.

Ok, so I’m not a car mechanic. My experience in that area is limited to occasionally topping up my own screenwash and once watching my Dad change some spark plugs. But I’m pretty sure that compressed air is, well, compressed air. As the sign itself makes clear, air is about 79% nitrogen and 21% oxygen (the numbers vary, but that bit, at least, is more or less right). Therefore, first problem, if you fill a tyre with compressed air you are by definition filling it with nearly 80% nitrogen.

In fact, I don’t think I’d want to drive a car with tyres which had been filled with pure oxygen and a bit of water, as the key suggests. Oxygen is a jolly effective oxidising agent. Tyres may not be the most flammable things in the world, but I reckon there’s a significant chance that your hot wheels would become a little more literal than you might like.

Moving on, in the round-ish tyre diagram there appears to be water, oxygen and nitrogen. Call me naive, but if you tell me you’re filling my tyres with nitrogen I’m going to assume it’s pure nitrogen. Whereas what you have there is (I’m so sad I counted and worked it out) 40% nitrogen, 27% water 33% oxygen. I dunno what that particular mixture is, but it’s not air and it’s definitely not pure nitrogen.

And then there are the captions underneath: “Undesirable components of the air are removed when the tyre is filled with nitrogen”.  Well not according to that diagram, because there’s still water and oxygen in it…

And, “nitrogen is the only inflation medium developed solely for the use of pneumatic tyre inflation”. What about compressed air then? Doesn’t that count as an ‘inflation medium’?

And, “maintains the correct tyre pressure for longer”. Well, actually I’m not sure about this one (there’s an interesting article here expressing some skepticism though). The Formula One website says that they do indeed fill racing tyres with “a special nitrogen-rich air mixture, designed to minimise variations in tyre pressure with temperature. The mixture also retains the pressure longer than normal air would.” The internet tells me Red Bull alone invested over $100 million in 2012, a significant chunk of which would necessarily have to be research and development. If anyone knows about the best stuff to fill tyres with, it’s Formula One.

But, there is a bit of a difference between cars that are designed to routinely get up to 200 mph and tyres that are designed to cope with temperatures comfortably over 100 oC, and your household runaround that averages 35-ish miles per hour. Let’s say I’m not convinced we’re comparing apples with apples here.

I also don’t understand those blue arrows coming out of the squarish tyre (why IS it that shape anyway?) They seem to suggest that water is escaping. But if so, why is it escaping from one tyre and not the other? And how permeable is rubber to water anyway? (Answer: not very, otherwise the welly boot would have been a bit pointless really.)

The one thing I do accept is that water might, possibly, have a small effect on tyre pressure. Water has an annoying habit of changing state at everyday temperatures. Just 1 millilitre of liquid water occupies over 1300 millilitres when it turns into a gas at atmospheric pressure and 25 oC. If it’s hotter (which it probably would be, if it had suddenly turned into gaseous water) it occupies even more space. Of course it’s more complicated than this because tyres aren’t at atmospheric pressure, but the point stands: if there’s water in your tyres the pressure would fluctuate a bit as they warm up. This’ll happen anyway, since in general gases expand as they warm up, but water could make the difference more significant.

But I checked, when compressed air is produced they take out most of the water. Most of it condenses when the air is compressed, and the condensate is simply removed. Then they use an air dryer and a filter as well. So I dispute the idea that there’s a lot of water in standard compressed air in the first place. (It has since been pointed out – see comments – that a lot of garages have their own air compressors, and that although they’re supposed to dry the air they may not do it very effectively, so there could be a fair bit of water in there, although there shouldn’t be…)

Anyway, my musings over gases were interrupted by having to pay the terribly big bill. It did seem like a lot for about 50 kg of rubber, but I’m assured that tyres with the correct depth of ridgy bits are quite important. They told me they filled them up with nitrogen for free.