Curriculum Notes

This demonstration is appropriate for instructional units dealing with types of reaction, descriptive chemistry of carbonates, or equilibrium.  (It demonstrates removing a product from an equilibrium process to drive the reaction to completion.)  The carbon dioxide/carbonic acid equilibrium aspect of this demo could be emphasized in a unit dealing with biological carbon dioxide transport and blood buffering systems. This demo can also be used to produce carbon dioxide gas for other demos.

Discussion

When the hydrogen carbonate (bicarbonate) ion is protonated by a weak acid such as acetic acid, it produces carbonic acid:

$$\ce {CH3COOH(aq) + HCO3^{-}(aq) -> CH3COO^{-}(aq) + H2CO3}$$

Which then decomposes to form carbon dioxide and water:

$$\ce {H2CO3(aq) -> H2O(l) + CO2(g)}$$

Since carbon dioxide is quite soluble in water, some of it remains in solution.

Materials

• 1 ea. 600 mL beaker
• ~150 mL of distilled white vinegar
• ~10 g baking soda in a small beaker
• large tray
   

Procedure

Put the beaker on the tray.  Pour the vinegar in the beaker.  Dump the baking soda in the vinegar.  It foams.  The tray will catch the spillage if it foams over the top of the beaker.

Safety Precautions

Avoid getting vinegar or baking soda in your eyes.  Wear goggles.  These household ingredients can be disposed down the drain.