h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

the other day i did some training to use a piece of fire fighting equipment, a breathing hood and we were told it contained potassium super oxide

what is potasium super oxide, what does it do and how does it work???

It is potassium oxide which has an extra oxygen attached.

It generates oxygen by reacting with carbon dioxide which produces water and then the water reacts with it to produce oxygen.

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that don't make sense??? where does the hydrogen come from and the carbon go???

4 KO2 + 2 H2O &#8594; 4 KOH + 3 O2
2 KOH + CO2 &#8594; K2CO3 + H2O
K2CO3 + CO2 + H2O &#8594; 2 KHCO3

Sorry I just told you the important reactions. The point of it is to produce the oxygen.

To add a little to the above and to maybe relate it to something you might recognise the oxygen molecule can be reduced (that is have electrons added to it) to generate negative ions.

So at oxidation state zero it is oxygen as you recognise it O2

At oxidation state -1 it forms a -1 charged ion called 'superoxide' O2(-)

At oxidation state -2 is forms a -2 charged ion called 'peroxide' O2(2-)
You may be more familiar with that particular species. It is popular in hair salons and such

Fully reduced oxygen - its most stable form - then breaks up into a single oxygen atom bearing a 2- charge. O(2-) - this is just simple oxide.
(although unlike peroxide and superoxide it's actually too highly charged to really exist in that form alone - it needs counterions to stabilise it - such stuff is very stable - rock for example is various forms of metal oxide)

Both superoxide and peroxide are highly reactive by the way. They really want to gain further electrons and become simple oxide.

Hence both peroxide and superoxide are strong oxidising agents will take electrons from many things they come into contact with in the drive to become oxide.
Superoxide can go the other way and be reduced to O2 though - which is what is happening in your example.

(oxidation an be defined as loss of electrons and is hence the opposite of the process of reduction I mentioned above)


Superoxide is a species also known as a (free) radical - that is, it has an 'unpaired' electron. Such species tend to be hideously reactive and are very destructive to flesh.
It is superoxide mostly (along with peroxide) that you are trying to reduce the levels of when you eat antioxidants.

Oxygen although vital for higher forms of life is one of the main causes of cell aging and destruction (and hence things like cancer) through the production of superoxide and peroxide as oxygen is used up in cells to generate energy.

According to wikipedia by the way, the reaction that is happening in your breathing hood is actually a reaction which is called a disproportionation.
That is the superoxide is both oxidising and reducing at the same time - to produce both a reduced and an oxidised form of oxygen.

2 KO2 --> K2O2 + O2

2 x potassium superoxide ---> potassium oxide + oxygen(gas)

This just happens by heating the potassium superoxide

nicki what is<< &#8594;>>????

so its bad news if you get it on your skin??? we were not told that!!! what happens with skin contact??

we were told to exhale hard when you first put it on to help fill the resevoir and help activate it

the device at the back is called a potasium candle!!!

thanks for the info

That was a cut and paste arrow unless I miss my guess.

Yes it's oxidising and corrosive but you won't be exposed to it like that unless there's a major failure in your equipment.

Breathing hard into to it suggests to me that water is being used to activate it - that would imply Nicky's reactivity equations are the ones going on in your device after all.

but its nice to know what you have sat at the nape of your neck/base of your skull??

it might discourage people who think they are invulnarable with the hood on from dashing into a fire filled room and endangering themselves and others if they know what might happen if the integrity of the hood is compromised?!?!?!

souldn't an agent like that have warning symbols on it???

http://en.wikipedia.org/wiki/Chemical_oxygen_generator

I don't really know the rules on what symbols should be on such a thing. But yes I take your point.

My guess is such risks are surely built into the design and will be minimised.
Plus you don't really need very much KO2 to generate a lot of oxygen.

If you assume 1/2 of the superoxide turns into O2 gas in the reaction then 71g of KO2 is enough to generate 10 liters of O2 - that's a lot.

Here's some safety info about it:

"Potential Acute Health Effects:
Hazardous in case of skin contact (irritant), of eye contact (irritant), of ingestion, of inhalation. Slightly hazardous in case of eye contact (corrosive). Corrosive to eyes and skin. The amount of tissue damage depends on length of contact. Eye contact can result in corneal damage or blindness. Skin contact can produce inflammation and blistering. Inhalation of dust will produce irritation to gastro-intestinal or respiratory tract, characterized by burning, sneezing and coughing. Severe over-exposure can produce lung damage, choking, unconsciousness or death. Prolonged exposure may result in skin burns and ulcerations. Over-exposure by inhalation may cause respiratory irritation."

Not terribly nasty, by the look of it.

they are good for 15 minutes

liked the bit in the wiki article that they explode if the become contaminated with oil