Chemical Leak - Manchester
Discussion
http://www.bbc.co.uk/news/uk-england-manchester-20...
It's been a while since I did Chemistry but isn't this bad "Firefighters are dousing the acid with water."?
If I remember the rhyme adding water to acid is bad (generates the gas?)
It's been a while since I did Chemistry but isn't this bad "Firefighters are dousing the acid with water."?
If I remember the rhyme adding water to acid is bad (generates the gas?)
for a start, if it's gas, it's hydrogen chloride gas and not hydrochloric acid gas (which is nothing).
if you've got a lot of HCl escaping then spraying it with water is not a bad idea as it should go into solution and then can in principle just be washed away. much better than clouds of HCl everywhere.
adding water to acid is ok but adding concentrated acid to water is not always the best idea (depending on concentrations you can get away with it - i always forget which way round is the 'sensible' way).
if you've got a lot of HCl escaping then spraying it with water is not a bad idea as it should go into solution and then can in principle just be washed away. much better than clouds of HCl everywhere.
adding water to acid is ok but adding concentrated acid to water is not always the best idea (depending on concentrations you can get away with it - i always forget which way round is the 'sensible' way).
"For heaven's sake do as you ought'a - add the acid to the woughta (water) If you think your life's too placid, add the water to the acid" ok it works in a cockney accent.
It applies mostly to sulphuric acid because:
- the reaction between it and water is highly exothermic,
- water is far lighter, and
- sulphuric acid is a poor conductor of heat.
The water thus spreads out on the top causing a large surface area for a violent reaction to take place which boils the layer water at the surface and spits out the acid water mix, which will be very concentrated.
If you add acid to the water it sinks down in a lump with a lower surface area thus a slower reaction, and the falling movement and mass of water will allow enough cooling to avoid boiling.
You still have to add it slowly.
In dilute acid the reaction is obviously less exothermic so there is less risk.
It applies mostly to sulphuric acid because:
- the reaction between it and water is highly exothermic,
- water is far lighter, and
- sulphuric acid is a poor conductor of heat.
The water thus spreads out on the top causing a large surface area for a violent reaction to take place which boils the layer water at the surface and spits out the acid water mix, which will be very concentrated.
If you add acid to the water it sinks down in a lump with a lower surface area thus a slower reaction, and the falling movement and mass of water will allow enough cooling to avoid boiling.
You still have to add it slowly.
In dilute acid the reaction is obviously less exothermic so there is less risk.
Ian Lancs said:
hornet said:
Billy was a scientist
He isn't any more
For what he thought was H2O
Was H2SO4
About the only thing I remember from chemistry
Now I remember that as well - wonder what piece of useful information I've just replaced....He isn't any more
For what he thought was H2O
Was H2SO4
About the only thing I remember from chemistry
Marge: That's because you were drunk!
Homer (dreamily): And how...
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