Perform two demonstrations with a top-loading balance. The order in which you perform the experiments in class matters!

Take a screw cap vial, and fill it with vinegar. Wash the outside, and wipe dry. Place the vial in a zippered bag. Add a teaspoon of sodium bicarbonate to the bag, exclude the air from the bag, and seal. Weigh the bag. Unscrew the vial cap, spill the vinegar into the bag, and replace on the balance. Record weights.

Take a few mL of 1-2M NaOH, and seal the solution in a screw-cap vial. Rinse the outside, and wipe dry. Place the sealed vial in a zippered plastic bag. Somehow fill the bag with carbon dioxide. Dry ice would work. You can produce CO₂ in a large beaker with bicarbonate and vinegar, and then "pour" the gas into the bag. Seal the bag, place it on the balance, and weigh the bag. Then open the vial and spill the basic solution into the bag. Record weights.

Discuss these experiments in class.