Chemical bartender

Procedure

• Prepare the following 4 solutions:
  • Solution A: Dissolve 24 g of BaCl₂2H₂O in 100 mL of water.
  • Solution B: Dissolve 25 g of Na₂S₂O₃5H₂O in 100 mL of water.
  • Solution C: Dissolve 21 g of Na₂CO₃ in 100 mL of water.
  • Solution D: Dissolve 0.4 g of KMnO₄ in 100 mL of a 2 M sulfuric acid solution and dilute to 1 L with water.
• Prepare 5 precipitation flasks and add:
• 1: Nothing.
• 2: 1 mL of the Na₂S₂O₃5H₂O solution.
• 3: 1 mL of the Na₂S₂O₃5H₂O solution and 3 mL of the BaCl₂·2H₂O solution.
• 4: 3 mL of the BaCl₂2H₂O solution.
• 5: 1 mL of the Na₂S₂O₃5H₂O solution and 3 mL of the Na₂CO₃ solution. These volumes are so small that they are barely visible.
• Add about 200 mL of the KMnO₄ solution to each precipitation flask and observe what happens.

Theoretical explanation

The approximate concentrations of BaCl₂·2H₂O, Na₂S₂O₃·5H2O, and Na₂CO₃ are 1 M. The concentration of KMnO4 is 0.0025 M.

The reactions that take place are:

2 MnO_4^– + 16 H⁺ + 10 S₂O_3^–    2 Mn²⁺ + 5 S₄O_6^2- + 8 H₂O
Ba²⁺ + SO_4²–    BaSO₄
CO_3^2- + 2 H⁺    H₂O + CO₂