Battery Acid

[gonfishing]

O.K I know that the acid should always be added to the water, and not vice versa,
My young crew member has asked Why? My explanation of "it will explode" doesn't seem to be adequate So what is the Science / Chemistry behind this ?

Julian

 

[Nauti Fox]

Don't know the chemistry,but you always start by filling them with acid.

 

[tinstaafl]

My understanding is that it's only REALLY dangerous when adding water to sulphuric acid. Nitric and hydrochloric acids are less reactive. Probably still not a good idea.

It happens because the reaction is extremely exothermic meaning it generates a lot of heat. It therefore boils the water very quickly. If there is a lot more acid than water then this reaction will be very fast and can result in boiling water and acid being splashed and spat around. Which is funny to watch from a distance!

Is this enough or do you need more? How old is the child anyway? Can't you just say "because" when he/she asks why? /forums/images/graemlins/wink.gif

tinstaafl

 

[Wiggo]

For reasons that escape me, when the concentrated acid mixes with water, it gives off heat (I think it breaks down from say H2SO4 to 2H+ and SO4-- ions, f'rinstance). If you drop acid into water, a small amount ofd acid heats up a large amount of water, so not much temp change. Do it the other way round, and the water you dropped into the acid gets so hot it boils (lots of acid, heating not much water). In fact, it boils rather explosively, and the steam explodes from inside the body of the acid, showering everyone around with concentrated battery acid. Overall, scientists consider this to be a bad thing.

 

[Brooksa]

When you mix water and acid heat is produced ( don't know why with pure water, but it does).

If you add acid to water, the large volume of water convects to keep the temperature ris eto a minimum.

If you add water to acid, the smaller globs of water, completely surrounded by acid, rapidly heat to boiling point and then boil, spitting acid out with the steam.

Tony Brooks

 

[gonfishing]

She is 14 so not so easily fobbed of

 

[cliff]

One NEVER adds water to acid - always add the acid to the water even if Nitric of Hydrochloric or even Acetic.

Simply put, for the chemically challenged, by adding the acid to the dilutant the acid is rapidly diluted and adding more acid (slowly) slowly increases the concentration. Doing it the other way round, one starts with a high concentration and work slowly downwards allowing the heat of dissociation to boil the dilutant (assuming water). If using other dilutants the resulting solution can be extremely (explosively) unstable over a given concentration of acid to dilutant therefore one always works from weakest strength upwards.

I made a ooopsie once and literally wrecked the laboratory, fortunately no one was injured - just my pride - took some explaining to the "boys in the checkered bonnets" though, not to mention the MD who did not have any sense of humour. /forums/images/graemlins/crazy.gif

 

[brianrunyard]

Dilute acid