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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Are you (still) a chemist and you didn’t know it?

I recently wrote a post listing five bits of chemistry you (probably) do every day.  It was surprisingly popular and so, just like the big movie companies, here’s the sequel!

Picture 0151.  Make fresh coffee (or at least drink one someone else made)
Espresso (the basis of most coffee drinks) is made by forcing a small amount of very-nearly boiling water through ground coffee beans.  This handily extracts a number of chemicals including all the ones that produce the lovely coffee flavours and aromas but also, crucially, our friend caffeine, without which many of us simply wouldn’t function on a daily basis.  What you (or your favourite barista) have done here is a form of chemical extraction.  Extraction techniques are extremely important in chemistry, because nature has an annoying habit of stirring up the stuff we want with lots of other things.  Chemists, especially the organic ones (produced with all-natural fertilisers) spend most of their lives carefully and painstakingly extracting things from other things. Some of them probably earn less than baristas, too.

2.  Make toast
You know when you make the perfect slice, and it goes that lovely brown colour, just before black?  That’s the Maillard reaction in action.  It’s the same thing that happens when you brown meat, chips, onions or, well, anything else that goes brown when you cook it.  It’s a reaction between amino acids (the stuff proteins are made of) and sugars.  It’s also responsible for those lovely toasted-biscuity smells and favours.  The surface of the food has to be in contact with dry heat for this reaction to happen, which is why boiled and microwaved food doesn’t brown.  And alkaline conditions help it along, which is the main reason lye is traditionally used on the surface of pretzels and other German breads (that’s always made me a bit nervous).

Haemoglobin3.  Breathe
I mentioned respiration in my previous post but as any 13 year-old pupil will tell you, and most adults have long since forgotten, respiration is not the same as breathing.  Here I’m actually thinking of oxygen exchange (which is also not, technically, the breathing bit but bear with me).  You’re probably aware that you blood has iron in it: in fact that iron is tied up in rather beautifully complicated haemoglobin molecules.  Oxygen molecules bond to four iron atoms in the haemoglobin with something called coordinate, or dative covalent, bonds.  If it weren’t for this nifty bit of chemical bonding, there’s no way our blood could carry enough oxygen around our bodies, delivering it safely to our cells, to keep us going from one minute to the next.

251840969_6404.  Neutralised some excess acid
Taken an indigestion tablet recently?  Did you realise you were doing a chemistry experiment in your very own stomach?  Well you were!  Indigestion tablets contain a variety of substances, but some of the most common ingredients are magnesium hydroxide (also known, when suspended in water, as ‘milk of magnesia’), calcium carbonate, sodium bicarbonate and magnesium carbonate.  These are all bases: they react with acids to form a salt and water and, in the case of the carbonates, carbon dioxide as well.  The acid in your stomach is hydrochloric acid, so for example:

sodium bicarbonate + hydrochloric acid –> sodium chloride + water + carbon dioxide

Now, is that Rennie advert that claims to “turn acid into water and other natural substances” starting to make sense?  They don’t want to use the word salt for some reason…

5.  Used drain cleaner
This is one of my favouritist little bits of chemistry.  Really.  It’s lovely.  Well apart from the horribly caustic chemicals involved obviously.  Drain cleaner is dangerous concoction nasty stuff but it’s main ingredient is often a strong alkali, like sodium hydroxide (there are also acidic drain cleaners; it’s quite important that you don’t mix them).  The stuff that blocks up your plughole is, largely, protein (hair, skin cells, yuck) and and oily dirt.  The strong alkali reacts with these things in a reaction called hydrolysis.  Now this is clever, because soap is made by (virtually) the exact same reaction.  Soap is produced by saponification, where fats are mixed with a strong alkali.  So what are you doing when you put drain cleaner in your stuffed-up plug hole?  You’re not only breaking down the gunk, you’re also effectively making soap in situ, which helps to wash away the remaining dirt.  How brilliant is that?

With thanks to Andrew (@_byronmiller) for his suggestions.

Are you a chemist and you didn’t know it?

When I tell people that I’m a chemist, I often get an “oooh, I was really bad at that at school” type response. It’s surprising the number of people that think chemistry has nothing whatsoever to do with their daily lives. Memorably, one acquaintance of an acquaintance (I wouldn’t go so far as to say friend of a friend) once even proclaimed, quite proudly, that the whole of science had nothing to do with her, and she lived her life entirely without it. I was so gobsmacked I didn’t really know where to start, and trust me, that doesn’t happen often.

washing-hands--soap-jpgSo with that in mind, here are five bits of chemistry you do every day. Or at least regularly. You’re a chemist and you didn’t know it!

1. Wash your hands.
Well, we all hope you do this one every day anyway. Soap is very clever stuff. It’s one of the oldest bits of chemistry there is, going back thousands of years, when people first discovered that if they washed their pots with the ashes of cooking fires they got a better result. Soap is made by a process called saponification, where fats are mixed with strong alkalis (traditionally lye: sodium or potassium hydroxide). The fats break apart and form fatty acid salts. What’s clever about those, is that they have a water-loving end (the salt bit) and a water-hating end (the fatty acid bit). So they can grab onto both, and hold the water and oil together. That’s what you do every time you use soap: the dirt ingrained in oil on your skin (nice) can, with the help of those lovely soap molecules, mix with water and so be washed away. Brilliant!

2. Drink a pH indicator.
‘What’ I hear you cry, ‘I do no such thing!’ Ah but do you drink tea (the black kind)? If so, then you do, even if you’ve never noticed. Have you ever put lemon in your tea instead of milk? If not, and you have tea and lemon juice (bottled is fine) in your house, go and try it now. The colour change is really quite lovely to watch. Lemon juice is a source of ascorbic and citric acids, and has a pH of roughly 2-3. You’ll see the same effect with vinegar too, although that mixture wouldn’t be quite so nice to drink. (If you’re feeling adventurous, try some common alkalis such as baking soda or bleach, but DEFINITELY don’t drink those concoctions afterwards…)

3. Carry out combustion.
Ever lit a match? Or a lighter? Started your gas cooker? Turned on your gas boiler? Started your petrol or diesel car? Of course you have. Every single time you do any of those things, the carbon atoms in their molecules are reacting with oxygen to produce carbon dioxide and water. And even if you live under a damp and fireless rock, you’re still doing it – respiration, the process by which all your cells obtain energy – is a form of combustion.

4. Watch some ice float.
Ice floats. Stop press!
We take that for granted, but it’s amazing really. This is a brilliant bit of chemistry that has its tendrils in physics and biology too. Solids don’t generally float on their liquids. Solids are usually more dense than their liquid form, so they sink. But if water behaved like that we wouldn’t have life on this planet, because every time any body of water got really cold it would freeze from the bottom up, taking out all the life swimming in its depths in the process. Since we’re fairly sure that life began in the oceans, evolution would have come to a full stop. But water doesn’t behave like that; water expands when it freezes. Why? Because water has something called hydrogen bonds between its molecules, and as it solidifies these bonds increasingly force the crystalline structure to be very ‘open’. As a result, ice is actually less dense than water, so it floats. This is also why ice is so brilliant at cooling liquids; the warm stuff rises, hits the cold ice and sinks again, creating a sort of cycle called a convection current. Who knew there was so much sciency stuff in your spritzer?

5. Bake a cake.
Food is a rich source of chemistry, just ask Heston. In this case, I’m thinking of baking soda, otherwise known as sodium hydrogencarbonate, or sodium bicarbonate (NaHCO3). When it’s heated above about 70 oC it undergoes a chemical reaction called decomposition. In other words, its molecules break apart without actually needing to react with any other substance. When you put baking soda into your recipe, or use ‘self-raising’ flour (which has it already added), you’re setting it up for this chemical reaction. As the cake cooks, the mixture heats up, and the baking soda does this:
2NaHCO3 –> CO2 + H2O + Na2CO3
The carbon dioxide, CO2, is a gas and it pushes your mixture up and out, causing it to rise. No baking soda chemistry, no lovely, fluffy cake.

So, next time someone tells you they’re rubbish at chemistry, you can point out that they’re doing it every day!