Sugar-acid dehydration reaction. Time-lapse footage of the dehydration reaction between sugar (sucrose, in beaker) and concentrated sulphuric acid. Sulphuric acid is a powerful dehydrating agent. When it comes into contact with a substance that contains hydrogen and oxygen, the elements of water, it removes those elements. Sucrose is a carbohydrate and made up of carbon, hydrogen and oxygen. By the end of the reaction, the sulphuric acid has removed the hydrogen and oxygen from the sucrose, leaving just carbon.