Question

Why sugar chars (turns black) when conc. H2so4 is added to it?

Answer 1

When we add concentrated sulfuric acid to sugar the result is interesting. The sulfuric acid is dehydrating agent and it dehydrates the carbohydrate sugar, removing the water and heating it into steam leaving behind a carbon foam. Thats why it looks black.

Answer 2

because the dehydration of sugar occour

C12H22O11 (sugar) + H2SO4 (sulfuric acid) → 12 C (carbon) + 11 H2O (water) + mixture water and acid