Bevin ? of King's High School asks :-

Why does acid burn skin and other materials?

Jim Simpson, a chemist at the University of Otago, responded.

First of all we must recognise that the effect of an acid depends very much on whether it is concentrated or dilute, that is to say how much water the acid is dissolved in.

Citric acid occurs naturally in lemons, tartaric acid in grapes and lactic acid in sour milk, indeed the name acid comes from the Latin word acidum which means sour. In these cases the acids are quite dilute and are not harmful. The effects that you describe in your question are more likely to be found in concentrated solutions of mineral acids such as sulfuric acid, which has the chemical formula H2SO4. Concentrated sulfuric acid is commonly used in car batteries.

Sulfuric acid dissolves readily in water in a process that gives out a great deal of heat and thus could produce a burn. It can also remove water from chemical compounds found in the skin and will react to destroy many organic compounds, including skin and soft tissue, in a process known as oxidation. The destructive power of sulfuric acid is considerable; it will even dissolve bone! Naturally one should always be extremely careful when handling any strong acid. Safety glasses and protective clothing should always be worn. If an accident occurs and sulfuric acid is spilt, sodium carbonate should be spread over the liquid as it will neutralise the acid.