Limiting Reagent (Baking Soda with Vinegar)

Purpose:

To demonstrate the concept of limiting reagents.

Materials:

• 5 250mL Erlenmeyer flasks
• 5 balloons
• Stir plate
• 5 magnetic stir bars

Reagents:

• Sodium bicarbonate (NaHCO₃)
• Acetic acid (CH₃COOH)

Hazards and PPE:

• Wear approved safety goggles and gloves.

Protocol:

Preparation

1. Label Erlenmeyer flasks 1-5. Pour 150mL acetic acid into each flask and add a stir bar to each.
2. Loosen the balloons that are going to be used by stretching them out (this will make it easier for the balloons to expand during the reaction).
3. Use a funnel to transfer the following amounts of sodium bicarbonate into the balloons and then attach the balloons to the appropriate flasks without letting the sodium bicarbonate spill into the acetic acid.

   1. Flask	Mass sodium bicarbonate (g)	Moles sodium bicarbonate	Volume acetic acid (mL)	Moles acetic acid	Limiting reagent
      1	3.3	0.039	150	0.1248	Sodium bicarbonate
      2	5.7	0.0678	150	0.1248	Sodium bicarbonate
      3	10.5	0.1248	150	0.1248	Equal
      4	21.0	0.2502	150	0.1248	Acetic acid
      5	31.8	0.3786	150	0.1248	Acetic acid

Demonstration

1. Place flask 1 on the stir plate and dump the sodium bicarbonate into flask 1 with the balloon.
2. Ask the audience what is going to happen when you dump the sodium bicarbonate into flask 2.
3. Repeat this process for the other flasks.

Additional Notes:

• These reactions will likely result in an overflow of liquid into the balloon. You may need to hold the balloon in place until the reaction completes. After the most vigorous portion of the reaction, gently hold up the balloon and allow the contents to drain back into the reaction flask.

Disposal:

• All solutions can be poured down the drain with excess water and balloons can be thrown away.

Reactions:

• CH₃COOH_(aq) + NaHCO_3(aq) → CO_2(g) + H₂O_(l) + NaC₂H₃O_2(aq)

Citations:

1. Dr. Feldwinn Demo Library, UCSB.