Materials
Baking soda (varying amounts: 5g, 10g, 15g, 20g)
White vinegar (100ml per trial)
Plastic bottles (500ml)
Balloons
Measuring tape
Kitchen scale
Funnel
Procedure
1. Pour 100ml of vinegar into a plastic bottle.
2. Place a measured amount of baking soda into a balloon using a funnel.
3. Stretch the balloon over the bottle opening without dropping the baking soda in.
4. Lift the balloon to dump the baking soda into the vinegar.
5. Measure the balloon's circumference once inflation stops.
6. Repeat 3 times per baking soda amount.
7. Calculate approximate volume from circumference.
Observations
5g baking soda: avg balloon circumference 28cm. 10g: avg 41cm. 15g: avg 48cm. 20g: avg 49cm. The jump from 15g to 20g was minimal — the vinegar appeared to be the limiting reagent at that point. Reactions with 15g and 20g produced visible foaming inside the bottle. One 20g trial balloon slipped off during reaction.
Notes
Demonstrates the concept of limiting reagents in an accessible way. The plateau between 15g and 20g is the key teaching moment. For 100ml of 5% acetic acid vinegar, stoichiometry predicts ~7g of baking soda should fully react. The excess beyond that is clearly visible.