Sugar worm

Procedure

• Weigh 40 g of sugar and place them in a beaker.
• Measure 12 mL of sulfuric acid.
• Carefully add the 12 mL of sulfuric acid to the beaker with sugar. Work inside the fume hood.
• Stir well with the glass stirring rod, for about a minute, until the sulfuric acid has mixed with the sugar.
• Let it sit for 2 or 3 minutes and observe the reaction.

Theoretical explanation

One of the most spectacular demonstrations of chemistry is also one of the simplest. It’s the dehydration of sugar (sucrose) with sulfuric acid. Sulfuric acid removes water from the sugar in a strongly exothermic reaction, releasing heat, steam, and sulfur oxide gases. Besides the sulfur smell, the reaction produces a caramel-like odor. The white sugar turns into a black carbonized tube that comes out of the beaker, hence the name “worm.”

Sugar is a carbohydrate hydrate, so when water is removed from the molecule, it dehydrates and breaks bonds, forming carbon, water, and a mixture of other gases.

C₁₂H₂₂O₁₁ + H₂SO₄   12 C + 11 H₂O + H₂SO₄

Although the sugar dehydrates, the water is not lost but rather remains in a liquid state with the sulfuric acid. When sulfuric acid comes into contact with water, a highly exothermic dilution occurs (releasing energy in the form of heat), causing the water to evaporate and propel the carbonized sugar mass outward.

Simultaneously, there is a process of oxidation of the carbon atoms present in the sugar molecule by the action of sulfuric acid. Carbon dioxide and sulfurous acid are obtained, which rapidly decomposes into sulfur dioxide and water:

Oxidation: C + 2 H₂O   CO₂ + 4 H⁺ + 4 e^–
Reduction: SO_4²– + 2 H⁺ + 2 e^–    SO_3²– + H₂O
Overall process: C + 2 H₂SO₄   CO₂ + 2 H₂SO₃
At the same time: H₂SO₃   SO₂ + H₂O