The Black Snake

Alternate titles:

Dehydration of Sucrose

Purpose:

To demonstrate chemical versus physical change and a chemical process of dehydration.

Materials:

• 100mL beaker
• Glass stir rod
• Low plastic bucket
• Paper towels
• Tall form 250mL beaker

Reagents:

• Conc. sulfuric acid (H₂SO₄)
• Sucrose

Hazards and PPE:

• Sulfuric acid is acutely corrosive and toxic. Avoid skin contact and inhalation of fumes.
• Wear approved safety goggles and gloves.

Protocol:

Preparation

1. Add 50g sucrose to beaker.
2. Place beaker on mat of paper towels in plastic bin.
3. Measure out and cover 50mL H₂HO₄ in 100mL beaker.

Demonstration

1. Add H₂HO₄ to beaker of sucrose.
2. Stir vigorously and briefly, then step back.
   1. Color will change from white, to yellow, to brown, to black.
   2. A column of black, carbonaceous foam will rise from the beaker.

Disposal:

• The black material can be broken out of the beaker and placed in a properly labeled waste container. Extra care should be taken when removing the material from the bottom of the beaker as it may contain some remnants of the concentrated acid. The beaker can then be washed and cleaned normally.

Reactions:

• C₁₂H₂₂O_{11 (s)} + H₂SO₄ → C_(s) + H₂O_(g) + H₂SO_4(hyd) + ΔH

Citations:

1. Shakharshiri, Bassam. Chemical Demonstrations, Volume I, 1983.

Videos:

• Black Snake Demonstration - Chemistry | Massey University

  Massey University