Brady and Neil thought it might be fun to try and add a piece of metallic Lithium to 7 Up
The reason for this is that long ago 7 Up used to contain Lithium salts
So they thought it'd be a bit of a joke
They bought a bottle of 7 Up... this is not product placement
and they poured some into a beaker and dropped in a piece of Lithium
Of course it bubbled - partly the CO2 coming out of the fizzy drink, partly the hydrogen from the reaction
But what was surprising was that the solution started to go pale green and then it went to reddish brown colour
and by the time I went to the lab, (it) looked like beer
The obvious first stage is Lithium metal reacts with water to form Lithium hydroxide which is an alkali
That alkali might react further with the other components of 7 Up
And if you read about it, it contains sugar, natural lemon and lime flavor, whatever that is,
and it also contains "no caffeine" so there's no caffeine chemistry here
The first question is how would the acidity or alkalinity of the solution change
So we measured the pH of fresh 7 Up
which turned out to be slightly acidic, as you might expect, if you dissolved carbon dioxide into water
And we measured the acidity of the 7 Up plus Lithium
and again as expected it was pretty alkaline
So a possible explanation for the colour is that it was produced by the alkaline conditions
and the alkali was causing a reaction of the other components of the 7 Up
Lithium salts are completely colourless. They're all white just like table salt
So the question is why is it going coloured and brown
I suggested an experiment
If it was the alkali, we should get a similar effect if we put Sodium Hydroxide, which is a strong alkali, into some 7 Up
To begin with nothing happened
Neil and Brady got quite excited
"The Professor's wrong!"
You see, one up for them
But then as we watched, the pellets of Sodium Hydroxide started developing a red colour
almost as if they were bleeding
It was really rather beautiful
and the colour began to develop
It was reacting slowly - much more slowly than the reaction that we saw with Lithium
We noticed that the Lithium hydroxide one - the one that we put the lithium metal in - the solution was quite hot
And Neil dipped a thermocouple into the Sodium Hydroxide plus 7 Up
and found that the surface was nearly at room temperature
but down where the colour was developing, it was quite warm - nearly 50 degrees
You might say, "Why wasn't it convecting?"
Well of course the concentrated solution of Sodium Hydroxide is very dense
so you get less convection than you would normally in water
We added some more Sodium Hydroxide and the colour developed
And so, the reason why temperature is important is because
most reactions of organic compounds, like the sugars in the 7 Up, double their rate for each 10 degrees centigrade that you go up
So if you go from room temperature, 20 to 30 to 40 to 50, the rate will go up about 8 times - doubling each time
So that would explain the difference
By this time, the Lithium beaker was looking pretty dark
and you couldn't really tell what colour it was
So I suggested that we dilute it a bit into water
So we got a beaker of water, not 7 Up, just pure water and added a little bit of the solution
and it looked as of yellowy brown colour
Suddenly I thought perhaps whatever coloured compound we'd made might be an indicator
you know that changes colour when we go from acid to alkaline
So Neil had some concentrated Sulfuric acid which is a bit fierce
so he diluted that and we poured in the Sulfuric acid and much to my pleasure, it went completely colourless
So whatever we made changed colour depending on the pH, depending on the acidity
But then, I wondered what would happen if we added more alkali
And when we added more alkali
it changed back to colour
Now of course there are 2 explanations
The first one is we may have created an indicator out of 7 Up
The other explanation is that
whatever was reacting in the 7 Up, there was still some in the water and that reacted with the alkali again
So you can't be absolutely sure what happended in the final stage but it seemed to behave like an indicator
When we put in more alkali, it could be that that compound changed back
or, it could be that there was still sugar in the solution and we just made more of the starting compound
And you can't really tell the difference without more careful experiments
[Coke in Liquid Nitrogen] Looked like an artwork and I persuaded Brady and Neil that we should watch it melting