Bad Science - 2 - D:Ream, Things Can Only Get Better

"Things can only get better 

Can only get, can only get 

They get on from here 

You know, I know that 

Things can only get better"

D:ream, Things Can Only Get Better

In 1994, D:ream sang that "Things can only get better...", this is excusable as a catchy line in a pop song but in their midst was the man who would later become the high priest of physics - Dr Brian Cox.

As Dr Brian well knew things can, quite literally, only get worse. Due to a thing called entropy, given the symbol, S.

Entropy is a measure of the disorder of a system and for any closed system, the higher the entropy the higher the disorder. 

So for a closed system like the universe, total entropy must always increase, in other words, disorder can only increase, so things can only get worse.

Did the D:ream lead singer know any better? Did the D:ream lead singer care? I suspect not, after all, this was his one shot fame.

On the other hand Dr Brian, the beautiful smiling face of popular science, definitely knew better but as he was consigned to plonking away at the keyboards in the background (he is barely visible in the video above; and if you look at the picture below, it is not hard to see why the camera didn't focus in on him, he is on the far right) I suspect he didn't really have a say in it.

Brian Cox (far right) then... 

                                                    

  ....and now

So Brian, things don't get better, they invariably get worse, except for haircuts, which do appear to have improved over time.

Climate change just got serious

We've all heard it before, due to climate change summers will get warmer (woop, woop), there will be increased flooding (I live on a hill), polar ice caps will melt (they're only polar bears) but what about the indirect consequences of climate change.

The indirect effect of climate change is increased cost of food production including peanut butter, coffee, maple syrup, wine, honey and chocolate.

Yes, you read that right, CHOCOLATE! Climate change will affect the world wide production and therefore cost of chocolate.

So get off your backsides, turn off that TV, unplug the stereo and go and build a windmill.

This has just got serious.

Death by Chocolate

The toxicity of a substance is generally judged by a property called LD50 or Median Lethal Dose. LD50 is the mass of a substance that would kill 50% of the population in g/Kg. It is often calculated in rats or mice and then applied to humans, so there is therefore some ambiguity and variation in the accuracy of the values. Nevertheless, it is the best assessment of toxicity we have.

Here are some examples of LD50s (in g/Kg)...

Table Salt, 3
Vitamin C, 11.9
Capsaicin (the hot stuff in chillis), 0.0472

Which brings us to chocolate.

Chocolate contains a chemical called theobromine that accounts for its toxicity, Due to the theobromine content chocolate's LD50 (in humans) is 77g/Kg. Effectively that means that 6Kg of chocolate is enough to kill 50% of the population of people weighing 12 Stone.

To put it seasonally, that is approximately 20 average easter eggs or 60 bags of mini eggs or 300 creme eggs.

Now if you think that is disappointingly low, think of your dog. The LD50 for chocolate in dogs is about 26g/Kg. This means that 1kg of chocolate is enough to wipe out a pretty large dog and considerable less is needed to cause it some serious problems. Dogs can't metabolise the theobromine as well as humans so it can easily build up in their system. If you are worried that your dog has been at your choccies then the symptoms of theobromine poisoning in dogs are nausea, vomiting, diarrhea, and increased urination progressing to cardiac arrhythmias, epileptic seizures, internal bleeding, heart attacks and finally, death

So over Easter, take it easy with the eggs but make sure you eat them before the dog gets them. It might feel selfish at the time but you are doing them a favour in the long run.

What's the point of gritting the roads?

Have you ever wondered why we grit the roads? I know the obvious answer here is because it makes the ice melt, but why?  Why does gritting the road cause the ice to melt? Well, here is the answer to that question on a molecular level.

Grit (or Halite) is sodium chloride with all the impurities from mining left in. When it is added to ice It causes the freezing point of water to be lowered. So at, say -5C, pure water is solid but water with a touch of NaCl is a liquid.

This is all to do with equilibria, imagine a puddle that's freezing, solid water in the puddle is in equilibrium with the liquid water in the puddle and as freezing is an exothermic process at this low temperature freezing is favoured over melting and the water freezes.

Adding salt to the liquid water means that you are effectively "reducing the concentration of liquid water" because now it is not pure water it is water and salt. What difference does make to the equilibrium? Well, reducing concentration of a reactant favours the production of that reactant so liquid water is favoured over solid water and ice isn't formed.

Is this a special property of ice? Nope, any substance that dissolves in water will do the job, it's just that grit is cheap.

This also explains another weird effect. If you add salt to ice the temperature drops significantly, it can get down to -10C. This is because melting is favoured and melting is endothermic so the process of melting removes heat from the surroundings and drops the temperature.

Feel free to bore your friends with this explanation every time a gritter drives past over Easter.

World's Most Useless Machine

OK, this machine may be amazingly useless but I really want one. Even more to the point I want to know how to make one. Quality engineering using a recycled printer. Epic Win.

Materials Science

The BBC are currently running a series of pieces on the "Science of Materials" AKA Chemistry.

Nicely written and straightforward to read, the articles cover items such as:

Can we make a real working spiderman suit?
Can we make gadgets that repair themselves?
Are invisibility cloaks possible?

So if you are still snowed in or at a loose end go over to the BBC and have a read.

Bad Science - 1 - Busted, Year 3000

"I've been to the year three thousand
not much has changed but they lived under water,
and your great great great grand daughter,
is pretty fine"

Busted, that multitalented boy band from the early 2000s may not have really thought their lyrics through when they wrote this song abut time travel but their sloppiness regarding their exploits in the future really grate on me. The chorus (above) has two signficant inaccuracies, lets handle them one at a time.

"...your great great great grand daughter, is pretty fine" - Lets think this through, assuming that the great, great, great grandfather in this song was 25 when the song was released (about 2003), and assuming that he had a child at 30 and that all his descendants had children at 30. That would mean he would become a grandfather at 60, a great grandfather at 90 etc. So that his great, great, great grandaughter would have been born when he was 120 in the year 2098. She would have hit 25 in 2123. In which case in the year 3000 she will be 877 years old. Not an age at which most women are generally regarded as "pretty fine"

"...not much has changed but they lived under water..." - Now, I am not an expert on underwater life but I am pretty sure that if we did live underwater you couldn't describe it as "nothing much has changed". In fact I can barely think of any bigger changes than living underwater. If life underwater was like life above water then fish would look much more humanoid then they do.

Busted thanks for the catchy tune but next time think through your lyrics

Crystal Coordination Number

Background

Ionic compounds are made up of + and - ions (Na+ and Cl-) in a regular arrangement that is arranged so that + isn't next to a -. You would've thought that there is one or at best two or three ways of doing this, actually there are loads (visit this link to see 14 of them http://en.wikipedia.org/wiki/Crystal_structure#Lattice_systems of them) depending on the ratio of + to - ions and the relative sizes of + and - ions. Luckily for you, you only need to recognise and explain about two of them.

The two structures - NaCl and CsCl 

Think of a theoretical situation where all the ions are exactly the same size like in a box of bowling balls. When you have a box of bowling balls (or any identically sized spheres) the natural arrangement they will settle in will have each bowling ball being touched by 12 others (this is the maximum number of spheres that can touch a central sphere when they are all the same size, trust me its true!). 

Now to really exaggerate the situation imagine a similar scenario where you have a mixed bag of bowling balls and table tennis balls in a 1:1 ratio and for some weird reason when they arrange themselves naturally the bowling balls can only be touched by table tennis balls (and vice versa). Now there is a problem, because bowling balls are bigger than table tennis balls you can get maybe 50 around a bowling ball but in the reverse situation you can only get maybe 3 bowling balls to touch a table tennis. So in this theoretical box of bowling balls and table tennis balls there is a problem if you are to maintain this 1:1 ratio we can't have 50 of 1 and 3 of the other. So, the structure will have to take the smaller number of 3 as the number of each that touch each other. 

So now we have a pattern, when spheres are identically sized we can fit 12 around the opposite one, when they are different sizes this number decreases (down to possibly 3 for bowling balls and table tennis balls). This is called crystal coordination number. i.e. bowling balls have a crystal coordination number of 12. Mixed bowling balls and table tennis balls have a crystal coordination number of 3

Right to ions. 

Cs and Cl are v similar sizes (think bowling balls) so the crystal coordination number will be high (i.e. 8). Na and Cl are different sizes (think mixed bowling balls and table tennis balls) so the crystal coordination number must be lower (i.e. 6). 

This means that in the NaCl crystal there are 6 Nas next to every Cl and 6 Cls next to every Na.

The total crystal coordination number of the crystal is 6,6.  The crystal coordination number of sodium in the crystal is 6 and the crystal coordination of chloride in the crystal is 6.

What does NaCl and CsCl look like?

I am not going to try and draw this here so look at your notes or google them!

What are they going to ask you in the exam?

Firstly, there are the obvious questions like, what do they look like? what is the crystal coordination number? but what about the more descriptive questions that will involve a bit more thought.

1. Why do they have different crystal coordination numbers?

Cs is bigger than Na, so you can fit more Cl ions around a Cs than an Na. Hence CsCl is 8,8 and NaCl is 6,6

2. Why can't MgCl2 have a 6,6 coordination number?

In MgCl2 there are twice as many Cl ions as Mg ions and the crystal coordination number must reflect this, so the crystal coordination might be 4,8 or 6,12 or any structure that involves there being twice as many of one ion compared to another.