Chemistry vs Politics

The choice of chemicals that go into products that we buy off the shelves is not just determined by their performance.

There are several other factors in play – mostly marketing, but sometimes politics.

An excellent case in point is the insecticide Sevin. This was the first synthetic insecticide made that was lethal to insects without the undesirable properties of other synthetic insecticides such as organochlorines and organophosphates. That is. although it is toxic to insects, it is detoxified and eliminated rapidly in vertebrates and it is neither concentrated in fat nor secreted in the milk.

Before this came along the only insecticides with these properties were the synthetic pyrethroids, which are ultimately derivatives of naturally occurring pyrethrum.  It is for these properties that the pyrethroids dominate the domestic insecticide market, and are included in every can of fly spray you buy off the shelf.

So why have you never heard of Sevin?  The reason is purely political.  Sevin, despite its desirable properties, has an unfortunate legacy.  It was the insecticide being manufactured at the Union Carbide plant that resulted in the deaths of thousands of people in the worst industrial accident of all time – the Bhopal disaster.

In that particular case, the Sevin was not the chemical that killed people – it was one of the intermediates: methyl isocyanate.  Now, while methyl isocyanate is a deadly chemical, it is no more deadly than many other industrial chemicals in manufacturing plants around the world.  It only caused this great loss of life due to the appalling safety management of Union Carbide.

However, in the public eye, they now associate it with the Bhopal disaster, and for that reason, this extremely useful and safe chemical is essentially lost to us.

it’s a simple case of a marketing principle: perception is reality.  If the public perceives something to be true, then effectively it is true, despite what the facts and in this case science a very.

It’s exactly the same reason why after the Three Mile Island disaster, the Americans immediately stopped building nuclear power stations.  You of course know of the Three Mile Island disaster don’t you – it’s the only grand disaster in history with a casualty count of zero.

 

 

Suds and Cleaning.

Why do we like sudsing up our dishwater when doing dishes?

The obvious reason is that we think that the suds somehow contribute to the cleaning power.

This is not true, but there’s a reason why we think that. Before synthetic (sulphonated) detergents were invented, we used soaps to clean dishes.

The trouble with soaps is that calcium and magnesium in water would combine with them and render them ineffective, and the harder the water (higher mineral content) the bigger a problem it was.

The upshot was that the Ca and Mg would stop the soap foaming, so you had to use enough soap to the water to use up all the Ca and Mg, and have enough left over to do cleaning. So the lather test was to see if there was left over soap – if it didn’t make suds, then you didn’t have enough so you had to add more soap.

Synthetic detergents completely avoid this problem, because they don’t bind to the Ca and Mg, but we have been conditioned to associate Ca and Mg with cleaning ability.

Actually, truth be told, suds actually get in the way. Detergent that is sitting out of the water in suds would be better used in the water cleaning dishes. The other problem of course is that you have to rinse the suds off the dishes before you dry them.

So here’s how to wash. Fill the sink with dishes and water, and add the detergent LAST. When you add it, gently swirl it around so that it mixes, but don’t lather it.

Let the dishes soak for half an hour or so, so thatthe detergent molecules can go to work, and Bob’s your uncle.

Any persistent grime can then be removed with soda ash.

Where do Suds Come From?

There is nothing we love more than a good soapy lather when washing dishes.

What causes the suds, and why do we associate then with cleaning?

Well, those are two separate questions.  We’ll answer the first one today and the second one tomorrow.

Firstly, soap doesn’t make suds, it simply stabilises them.  If you squirt some detergent into a sink full of water, it doesn’t instantly suds up – you have to agitate it to cause some suds.  Actually, what you are doing is aerating it.  The agitation that you do mixes air in with the water, and it is these air bubbles that ultimately become the suds.

Without a detergent, the air bubbles simply float to the surface and pop.  Or, to put it another way, air bubbles don’t like being in the water, and the water doesn’t like having them there.  The reason is, that water is a polar liquid and the interface with air is unstable.  Therefore, bubbles are a lot worse because where there are bubbles there are lots and lots of interfaces.

So the air and water try to minimise the contact they have with each other by separating out into two separate phases with a single interface (the surface of the water) between them.

But with a detergent in there, things are different.  The detergent is a surface active agent (surfactant), and essentially it stabilises the interface.  So when you have made a bubble with your aeration, the bubble is now quite happy, as since surfactants love surfaces, they will coat themselves on both the inside and outside of each bubble.  In doing so, they balance the surface charges on the water molecules, and remove any need for the water to minimise its surface area.

So are suds a good indicator of cleaning power?  Well, the answer is both yes and no.  Tune in tomorrow for the answer.

 

Stain Removal #1: General Principles

The questions I get most commonly asked revolve around stain removal.  And it’s not just me – people like Shannon Lush have made a full-time career out of it.

For me, these questions are simply chemical questions.  That is, since everything we see and touch is a chemical, any question about stain removal is simply a question about how to remove one chemical from another.  Or, to be more exact, it is about how to make one chemical look as though it has been removed from another.

In general terms there are three approaches we may take:

1.  Separate the stain from the substrate.  This is the gentlest and by far the most common approach.  This is the role adopted by surfactants (detergents).  They separate the stain from the substrate (e.g. clothes or crockery) and allow it to be dissolved and carry it away.  If this approach doesn’t work, it may be for reasons such as that the stain has formed a bond of some sort with the substrate that is not easily broken.

2.  Destroy the stain either partly or wholly, without destroying the substrate.  This is particularly effective if the stain is a food dye or other natural or synthetic dye of some sort. These dyes tend to be large complex organic molecules that are very fragile – that is, they are easily susceptible to chemical attack.  And the most common form of chemical attack is oxidation with one of the many different types of bleach that are available.  All we have to do is destroy or modify one part of the molecule, and this often disrupts its electronic structure to the extent that the colour disappears.

This is also the domain of enzymes, highly specialised chemicals that specifically attack certain classes of stain.

The danger with this approach, of course, is that wherever you are oxidising a stain, you are potentially oxidising the garment as well.

3.  Remove the stain by removing part of the substrate that it is attached to.  This of course is not just a chemical approach – it is a physical approach.  If for example you had bore stains on something and you were unable to remove them chemically then you may remove them by scrubbing off the upper layer of paint that they are attached to.  Another example of this may be the removal of stains on cement by the use of hydrochloric acid to dissolve the upper layer of cement.

This approach does not, of course, apply to garments.

In subsequent posts I will dig into each of these approaches in detail, and describe the various ways in which stains maybe removed, disabled, or destroyed.

Asbestos – Nature’s Nasty Surprise

Last week, there was a fire in West Perth.  I don’t know anything about it other than what I heard on the news reports, in which their was concern that it may contain asbestos.

What is this stuff and why is it so nasty?

It has been around for many years and with the advent of the industrial age it has been used extensively in buildings as a result of some very desirable properties: it is an excellent insulator for heat and electricity, it is chemically resistant, and it is not prone to either UV degradation or biodegradation.

And as the knowledge of toxicology increased, and our understanding of the many complex pathways by which various industrial chemicals could interact with our body advanced, asbestos certainly raised no flags – it was, after all, nothing more than a silicon-based mineral.

But of course in the latter part of the last century it began to be linked with cancer, and that link is now well and truly established.

In a classic case of “oops – we didn’t think of that.”  the only attention that was paid to this material was its chemical properties, and no one considered the impact its physical properties could have.

In fairness, this is most likely because these properties were not understood in the same way that they are now.

Now remember something here – this nasty nasty material that has caused, and will cause, so many deaths, is a natural material. Like arsenic and cyanide it is natural.  So let’s not buy into this trendy view that natural things are good for us, and synthetic things are bad for us – it’s just nonsense.

Well, what exactly is the problem with asbestos?  And why don’t other types of dust cause cancer when we breath it in?

Well, as it happens, asbestos fibres fall into a critical size range.  Our lungs are full of tiny little compartments called alveoli, which are fed by billions upon billions of tiny little channels.  It turns out that if you breathe something in that is smaller than 1 µm, it just comes in and goes straight out again.  If we breathe in something that is greater than 10 µm, then it doesn’t get in.  But if something falls in the range 1 µm to 10 µm it is small enough to get in but not small enough to get out again, and so it gets stuck in there.

And it is generally thought that this foreign material, although it is chemically inert, is the cause of cancer.  Interestingly, there is a synergistic effect with cigarette smoke.  That is, if you smoke and have been exposed to asbestos, your chances of contracting cancer are far greater than the additive probabilities of the asbestos and cigarette smoke alone.  This also suggests some sort of physical mechanism.

In fact, this is one of the things that has come out of the 9/11 (shouldn’t we call it 11/9 in Australia?) terrorist attacks.

Although there were 3000 people killed when the buildings collapsed, there have been many others – an unknown number – that have contracted cancer as a result of breathing in the fine dust that the pulverised buildings created.

Due to the unprecedented force of the building collapse, microscopic and lethal dust particles (not ordinary dust, the pulverised building material, much of which probably was asbestos) filled the air in massive proportions and anyone who was unlucky enough to breathe at has been exposed to the risk of cancer.