Summary
A saturated solution of sodium bicarbonate is reacted with hydrochloric acid to form carbon dioxide gas. Universal indicator can be used to show the change in pH of the solution or an inflating balloon can be used to demonstrate the associated work done by the evolving gas.
Hazards
6M HCl is corrosive and toxic.
Chemicals and Solutions
- Saturated sodium bicarbonate solution (7g/100 mL H2O)
- Sodium bicarbonate solid
- 6M HCl
Materials
- Cylinder or Erlenmeyer (w/ side arm)
- Universal indicator
Procedure
- Place about 50 mL of saturated sodium bicarbonate solution in the tall cylinder.
- Add some sodium bicarbonate solid and several drops of indicator. The solution will have a green-blue color.
- Gently pour a small amount of 6 M HCl into the cylinder. Immediately the solution will fizz up and change the indicator to red.
Hint: If the HCl is added gently, only the top portion of the liquid will be red and the bottom will remain green-blue, with a yellow zone in between the colors. Additional small portions of HCl can be added until the sodium bicarbonate is consumed.
Or, replacing the cylinder with a side arm flask fitted with a rubber stopper. Attach a balloon to the side arm. After placing the sodium bicarbonate solution in the flask, add HCl and quickly stopper the flask. The carbon dioxide produced blows up the balloon. This reaction is an example of a chemical process which does work. (work = PΔV)
Discussion
The reaction:
\( \ce{NaHCO3_{(aq)} -> CO2_{(g)} + H2O_{(l)} + NaCl_{(aq)}} \)