Dehydration reaction. Image 2 of 2. Beaker containing the results of the reaction between concentrated sulphuric acid and sugar (sucrose). 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. The sulphuric acid has removed the hydrogen and oxygen from the sucrose, leaving just carbon.