Concentrated sulphuric acid ($\text{H}_2\text{SO}_4$) is a strong dehydrating agent. When it reacts with carbohydrates such as sucrose ($\text{C}_{12}\text{H}_{22}\text{O}_{11}$), it removes water molecules completely from the structure, leaving behind a black mass of elemental carbon (often called sugar charcoal). The reaction is represented as: $\text{C}_{12}\text{H}_{22}\text{O}_{11} \xrightarrow{\text{Conc. H}_2\text{SO}_4} 12\text{C} + 11\text{H}_2\text{O}$ Because intact water molecules are removed, this process is an example of a dehydration reaction.