Question

(1) Why are the wooden shelves on which concentrated sulphuric acid bottles are kept stained black?

(2) Why is concentrated sulphuric acid always added to water and not water to concentrated sulphuric acid? Why does the mixture get hot?​

Answer 1

(1) Concentrated sulphuric acid is a very powerful dehydrating agent. It removes atoms of hydrogen and oxygen in the form of water from the cellulose [(C₆H₁₂O₅)ₙ], leaving behind carbon. It is black carbon which appears in the form of black stains.

(2) Because of dilution of concentrated sulphuric acid with water is an exothermic reaction. If you add water to concentrated sulphuric acid, it can boil and split and you may get splashed by boiling acid. Water has a higher heat capacity than the acid, and so a vessel of cold water will absorb heat as acid is added.

Answer 2

Answer:

1) Concentrated sulphuric acid is a very powerful dehydrating agent. It removes atoms of hydrogen and oxygen in the form of water from the cellulose [C6H12O5 n ] leaving behind carbon. It is black carbon which appears in the form of black stains.

2) This is because the reaction between acid and water is highly exothermic and produces an enormous amount of heat. Hence, when water is added to acid, it results in vigorous boiling of the solution and the amount of heat produced is so large that it splashes the acid out of the container, which can result in acid burns.