Limiting Reagent

(see Fall 2007 variation below)

Materials: (4) 9" round balloons, (4) 125 ml Erl fl., sodium bicarbonate (NaHCO₃), acetic acid (for 1M HAc, dil. 57.5ml 17.4M HAc to 1 liter)

Reaction: (1)HAc + (1)NaHCO₃ --> H₂CO₃ + NaAc --> (~1)CO₂ + H₂O + NaAc

2:2 -- 0.10 mole (8.4g) NaHCO₃ + 0.10 mole HAc (100 ml 1M)
1:2 -- 0.05 mole (4.2g) NaHCO₃ + 0.10 mole HAc (100 ml 1M)
2:1 -- 0.10 mole (8.4g) NaHCO₃ + 0.05 mole HAc ( 50 ml 1M)
1:1 -- 0.05 mole (4.2g) NaHCO₃ + 0.05 mole HAc ( 50 ml 1M)

Procedure:

Pre-stretch (inflate, then deflate) balloons to be used. Add weighed NaHCO₃ to each balloon.
Fit a balloon onto each flask.
Tip balloons to introduce NaHCO3 into flask.
Observe balloon size as reaction proceeds to limit.

Illustration:

Mg + 2HCl variation:

add 100 ml 2M HCl to each of 3 125ml Erlenmyer flasks - 0.2 moles each
add Mg to each of 3 balloons in these quantities for each: 1.2g (0.05 mole), 2.4g (0.1 mole), and 4.8g (0.2 mole)
similarly to above, fit balloons to each Erl. flask, introduce Mg by tipping balloon contents into flask.

This reaction variation produces copious heat, foam, and misty vapors.
The reaction slows as it proceeds.
Higher concentration HCl (6M) produces so much heat that the balloon is easily broken by the heat and pressure.
Even at 2M HCl, the heat produced seems to lead to the balloon leaking the hydrogen product during the initial (hot) phase of the reaction.

Fall 2007 (Prof. Boering) variation:

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