Concentrated sulphuric acid is a powerful oxidizing agent. When it is added to sugar, the acid molecules react with the sugar molecules to break them down into smaller molecules, such as water, carbon dioxide, and carbon. The carbon atoms then react with the oxygen atoms in the air to form carbon dioxide, which is a black residue.

The reaction between sulphuric acid and sugar is a highly exothermic reaction, which means that it releases a lot of heat. This heat can cause the sugar to catch on fire, so it is important to be careful when handling concentrated sulphuric acid.

The reaction between sulphuric acid and sugar is also a very corrosive reaction, which means that it can damage the skin and other tissues. It is important to wear gloves and eye protection when handling concentrated sulphuric acid.

Here is the chemical equation for the reaction between sulphuric acid and sugar:

C12H22O11 + 12H2SO4 -> 11H2O + 12CO2 + 12SO2 + C