Why can the mixing of acids and bases be dangerous

[Da Apprentice]

I tried googling this topic and basically all I could find was sites saying they neutralise each other - I know that. But why is it that when you mix say a drop of pH 14 solution with a lot of pH 1 solution that they react rather violently and the acid sprays everywhere? If someone could maybe explain the reaction that takes place and why this occurs that would be great.

Thanks,

 

[Studiot]

The basic reason why chemical reactions occur is that energy is released. This energy is usually heat energy. As you will know from the chemical reaction known as burning (fire) the reaction can be pretty vigouous if lots if heat is released.

Now when you mix acids and bases (or even acids and water) the same thing happens. Heat is released by the chemical reaction.

Sometimes the heat is enough to promote a vigorous reaction. In this case the heat may not be able to escape quickly so heats up the reactants perhaps to form a gas before the reaction is over. Since there is some acid still about there is a danger that drops of this will be expelled (spat about) by the gas trying to expand.

Does this help?

 

[mcbud]

Also, depending on the base (and the acid as well), you can have products that can be unsafe and perhaps hazardous. For example, if you mix bleach (NaOCl, a base) with hydrochloric acid, you will generate chlorine gas, which is extremely toxic and irritating to the respiratory tract.

NaClO + 2 HCl → Cl₂ + H₂O + NaCl

That's one of the reasons not to mix bleach with household cleaners.

 

[Borek]

Basically mixture can get hot and start boiling, splashing around.

 

[Da Apprentice]

Yeah this helps heaps, Thanks

 

[epenguin]

Yes, the practical message is you need to be cautious, protected, supervised etc. when playing with such things or not do it at all.

It is all, as Studiot et al. say to do with energy.

Just complete that by saying that these strong acids and bases (and a large fraction of the things you will study in chemistry) are only there for anyone to play with because energy has been put into make them. E.g. to make caustic soda or caustic potash brine has been electrolysed in an energy-demanding process you will later study. They are not found in Nature. Or hardly. On Earth anyway.