A tale of chemistry, biochemistry, physics and astronomy – and shiny, silver balls

A new school term has started here, and for me this year that’s meant more chemistry experiments – hurrah!

Okay, actually round-bottomed flasks

The other day it was time for the famous Tollens’ reaction. For those that don’t know, this involves a mixture of silver nitrate, sodium hydroxide and ammonia (which has to be freshly made every time as it doesn’t keep). Combine this concoction with an aldehyde in a glass container and warm it up a bit and it forms a beautiful silver layer on the glass. Check out my lovely silver balls!

This reaction is handy for chemists because the silver mirror only appears with aldehydes and not with other, similar molecules (such as ketones). It works because aldehydes are readily oxidised or, looking at it the other way round, the silver ions (Ag+) are readily reduced by the aldehyde to form silver metal (Ag) – check out this Compound Interest graphic for a bit more detail.

But this is not just the story of an interesting little experiment for chemists. No, this is a story of chemistry, biochemistry, physics, astronomy, and artisan glass bauble producers. Ready? Let’s get started!

Bernhard Tollens (click for link to image source)

The reaction is named after Bernhard Tollens, a German chemist who was born in the mid-19th century. It’s one of those odd situations where everyone – well, everyone who’s studied A level Chemistry anyway – knows the name, but hardly anyone seems to have any idea who the person was.

Tollens went to school in Hamburg, Germany, and his science teacher was Karl Möbius. No, not the Möbius strip inventor (that was August Möbius): Karl Möbius was a zoologist and a pioneer in the field of ecology. He must have inspired the young Tollens to pursue a scientific career, because after he graduated Tollens first completed an apprenticeship at a pharmacy before going on to study chemistry at Friedrich Wöhler’s laboratory in Göttingen. If Wöhler’s name seems familiar it’s because he was the co-discoverer of  beryllium and silicon – without which the electronics I’m using to write this article probably wouldn’t exist.

After he obtained his PhD Tollens worked at a bronze factory, but it wasn’t long before he left to begin working with none other than Emil Erlenmeyer – yes, he of the Erlenmeyer flask, otherwise known as… the conical flask. (I’ve finally managed to get around to mentioning the piece of glassware from which this blog takes its name!)

It seems though that Tollens had itchy feet, as he didn’t stay with Erlenmeyer for long, either. He worked in Paris and Portugal before eventually returning to Göttingen in 1872 to work on carbohydrates, going on to discover the structures of several sugars.

Table sugar is sucrose, which doesn’t produce a silver mirror with Tollens’ reagent

As readers of this blog will know, the term “sugar” often gets horribly misused by, well, almost everyone. It’s a broad term which very generally refers to carbon-based molecules containing groups of O-H and C=O atoms. Most significant to this story are the sugars called monosaccharides and disaccharides. The two most famous monosaccharides are fructose, or “fruit sugar”, and glucose. On the other hand sucrose, or “table sugar”, is a disaccharide.

All of the monosaccharides will produce a positive result with Tollens’ reagent (even when their structures don’t appear to contain an aldehyde group – this gets a bit complicated but check out this link if you’re interested). However, sucrose does not. Which means that Tollens’ reagent is quick and easy test that can be used to distinguish between glucose and sucrose.

Laboratory Dewar flask with silver mirror surface

And it’s not just useful for identifying sugars. Tollens’ reagent, or a variant of it, can also be used to create a high-quality mirror surface. Until the 1900s, if you wanted to make a mirror you had to apply a thin foil of an alloy – called “tain” – to the back of a piece of glass. It’s difficult to get a really good finish with this method, especially if you’re trying to create a mirror on anything other than a perfectly flat surface. If you wanted a mirrored flask, say to reduce heat radiation, this was tricky. Plus it required quite a lot of silver, which was expensive and made the finished item quite heavy.

Which was why the German chemist Justus von Liebig (yep, the one behind the Liebig condenser) developed a process for depositing a thin layer of pure silver on glass in 1835. After some tweaking and refining this was perfected into a method which bears a lot of resemblance to the Tollens’ reaction: a diamminesilver(I) solution is mixed with glucose and sprayed onto the surface of the glass, where the silver ions are reduced to elemental silver. This process ticked a lot of boxes: not only did it produce a high-quality finish, but it also used such a tiny quantity of silver that it was really cheap.

And it turned out to be useful for more than just laboratory glassware. The German astronomer Carl August von Steinheil and French doctor Leon Foucault soon began to use it to make telescope mirrors: for the first time astronomers had cheap, lightweight mirrors that reflected far more light than their old mirrors had ever done.

People also noticed how pretty the effect was: German artisans began to make Christmas tree decorations by pouring silver nitrate into glass spheres, followed by ammonia and finally a glucose solution – producing beautiful silver baubles which were exported all over the world, including to Britain.

These days, silvering is done by vacuum deposition, which produces an even more perfect surface, but you just can’t beat the magic of watching the inside of a test tube or a flask turning into a beautiful, shiny mirror.

Speaking of which, according to @MaChemGuy on Twitter, this is the perfect, foolproof, silver mirror method:
° Place 5 cm³ 0.1 mol dm⁻³ AgNO₃(aq) in a test tube.
° Add concentrated NH₃ dropwise untill the precipitate dissolves. (About 3 drops.)
° Add a spatula of glucose and dissolve.
° Plunge test-tube into freshly boiled water.

Silver nitrate stains the skin – wear gloves!

One word of warning: be careful with the silver nitrate and wear gloves. Else, like me, you might end up with brown stains on your hands that are still there three days later…


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Is oxygen really that good for you?

dove oxygen shampoo officialI don’t find time for huge amounts of television these days, and certainly not adverts. But I recently caught an advert for Dove Oxygen Shampoo out of the corner of my eye, and it brought me up short. Of course, beauty products are full of nonsense generally. Think, for example, of L’Oreal’s famous ingredient, ‘Boswelox’. (A word which, thanks to the wonderful Karl Pilkington, has since acquired a whole new meaning.) A little while ago I wrote a post about a toothpaste that was claiming to contain ‘liquid calcium’ (if it were true, cleaning your teeth would be much more exciting, trust me). It’s just par for the course. Really, is there any point wasting valuable energy continuing to be annoyed by these things?

Well yes, actually. Because this kind of silly hogwash just reinforces the ridiculous ‘science is so terribly hard, oooh aren’t all the complicated words impressive?’ attitude that is so frustratingly prevalent in the world today.

Besides which, picking apart this kind of thing is practically the reason for the existence of this blog. So here goes.

Firstly, a few snippets from Dove’s website:

“Oxygen & Moisture shampoo, conditioner and finishing products are pumped with Oxyfusion Technology, a new generation of moisture. This system moisturises fine, flat hair, giving you hair volume.”

And clicking through a bit further:

“[the shampoo] provides conditioning ingredients fused with oxygen as it instantly dissolves on your hair and breathes life into it.”

Hm.

Let’s start with that last sentence. Firstly: it dissolves on your hair? What does that mean? I’m just going to mention here that the meaning of the word dissolve is taught in year 7 (first year, in old money) science in all secondary schools in this country, and has been for many, many years. So everyone should know it, even the employees of the media company that came up with this tosh. (If you don’t, and you’ve ever muttered anything whatsoever about slipping standards and/or grade inflation, shame on you.)

‘Dissolve’ usually refers to solids. Salt dissolves in water. Sugar dissolves in tea (yes all right, also mostly water). It means that the solid becomes incorporated into the liquid, forming a solution. I haven’t checked, but I’m assuming Dove’s shampoo is not solid, as that would make it rather difficult to get out of the bottle.

Ok, oils and fats dissolve in certain solvents (not water mind you), and they could feasibly be liquid and yet the word still applies. True enough. It’s possible that the original text was ‘dissolves the grease on your hair’ (more or less accurate enough), and some marketing guy said, ‘I like really love it, I really reaaaahhhly do, but can we just lose two words from the middle?’

And yes, I think it’s safe to assume their shampoo mixes with water, because that is quite an important feature of shampoo, but they haven’t said ‘dissolves in the water’, they’ve said ‘dissolves on the hair’, which does sort of give the impression that it’s your hair that’s somehow dissolving the shampoo. Which is just weird.

But misuse of the world dissolve is only a minor irritation. No, my bigger problem is ‘ingredients fused with oxygen’. What the Dove does that mean?

For years and years we’ve been told that oxidants are bad. Or at least, that antioxidants are good (although this hasn’t really been backed up by scientific studies).

Is it difficult to work out that oxygen is an oxidant? It’s the granddaddy of oxidants. It’s the oxidant that all the other oxidants were named after. Oxy/oxi – see?

Chemists have two definitions of oxidation, but they’re broadly equivalent. Oxidation can be thought of as gaining oxygen, or it can be thought of as loss of electrons. Electrons are the negatively-charged particles that surround atoms. I mention them because the phrase ‘free radicals’ often turns up in the same breath as ‘antioxidants’. Free radicals are atoms or molecules which have an unpaired electron. Electrons like to be paired up. They REALLY like to be paired up. When they’re not, they’ll do pretty much anything they can to get paired up. Unpaired electrons are, if you like, the desperate guy at the nightclub at the end of the night. This makes them incredibly reactive, which means they can cause cell damage.

Worse, this happens in a chain reaction – meaning that a single free radical can do an awful lot of harm. So where to antioxidants come in? Well, antioxidants react with free radicals and essentially stop them in their tracks.

oxygen cylinder

Don’t suck on this.

Jolly good. But you see where I’m going here? Oxygen is the complete opposite of this. Yes, we breathe oxygen. It’s quite important stuff. Certainly, if you run out of it you’re in trouble. But it’s far from harmless. The air we breathe is only about twenty-one percent oxygen. Too much oxygen is flat-out dangerous. Breathe air with something like 50% oxygen for any length of time and you risk damaging your lungs, eyes and central nervous system. Really. Hospitals control oxygen use very carefully, and scuba divers who use it have to undergo rigorous training. The fad for oxygen bars has caused real concern in some quarters.

What does ‘ingredients fused with oxygen’ mean? Does it mean Dove have somehow dissolved oxygen in their shampoo? I’m certain that it doesn’t, because this wouldn’t be stable, and it would likely cause your shampoo to ‘go off’ in some way very quickly. Does it mean that their shampoo contains an ingredient that releases oxygen somehow? Hydrogen peroxide famously does this, when it breaks down into oxygen and water. Of course hydrogen peroxide is used to bleach hair, so… probably not (and anyway, again, not stable).

I looked up the ingredients in Dove Oxygen Moisture shampoo (and I’ve reproduced them below). To be honest, looking at the list I’m drawing a blank. My suspicion is that they’re using ‘oxygen’ simply because it’s the latest trendy thing. Oxygen is common enough – water contains one atom of oxygen in every molecule for starters, so they’re safe with the idea that the shampoo contains oxygen in some form – just not elemental oxygen.

But, ok, if I had to pick something… there is an interesting ingredient called ‘guar hydroxypropyltrimonium chloride‘ in there. If that is the one that inspired them, I can see why they went with Oxyfusion Technology – guar hydroxypropyltrimonium chloride hardly trips off the tongue.

Sucrose

Table sugar (sucrose) – perhaps we should wash our hair with this?

620px-Guaran.svg

Guar gum – check your salad dressing. Another conditioning alternative perhaps?

I’ve picked that one out of the list partly because it has ‘hydroxy’ in its name. Now in reality, that just means it contains an -OH group or several. This isn’t anything particularly special, table sugar has eight of ’em. Guar hydroxypropyltrimonium chloride comes from guar gum, which in turn is made from guar beans. Guar gum is a food additive that’s used to thicken foods, and it turns up all over the place (check your salad dressing or ice cream).

Guar hydroxypropyltrimonium chloride has been shown to have conditioning properties, which explains its inclusion in shampoo (this is my other reason for picking it out). It probably does leave your hair feeling nice and soft. And it does have several -OH groups, so it arguably sort of works with the ‘conditioning ingredients fused with oxygen’ claim. In the sense that it has oxygen atoms chemically bonded to it. As does, you know, water.

There’s no way that it releases oxygen though. Now in fairness to Dove, that claim isn’t actually made explicitly anywhere, although the lovely bubbly imagery does its damnedest to imply it.

Bad-Hair-Day

Bad hair day?

And here’s the thing: even if you could, would you want to routinely use a product that releases oxygen directly onto your skin or hair? Given that oxygen is an oxidising agent, and is likely to cause cell damage in high concentrations? Just bear in mind what happens to hair that’s exposed to too much hydrogen peroxide.

And don’t even get me started on the dozens and dozens of moisturisers that claim to do the same. Really? Straight into your skin? There are even some products that claim to do both at once, which frankly is jolly clever. In the Doctor Who sense of clever. I.e. fictional.

But what I want to know is this: after years of anti-oxidant this, and anti-oxidant that, how have we managed to go in exactly the opposite direction without consumers saying ‘er, hang on a minute, surely this has to be a load of old boswelox?’

Ingredients in Dove Oxygen & Moisture Shampoo:
Aqua, Sodium Laureth Sulfate, Sodium Chloride, Cocamidopropyl Betaine, Glycerin, Citric Acid, Dimethiconol, Disodium EDTA, Guar Hydroxypropyltrimonium Chloride, Laureth-23, Parfum, PPG-12, TEA-Dodecylbenzenesulfonate, TES-Sulfate, DMDM Hydantoin, Sodium Benzoate, Amyl Cinnamal, Benzyl Alcohol, Benzyl Salicylate, Butylphenyl Methylpropional, Hexyl Cinnamal, Limonene, Linalool, CI 17200, CI 42090.