At school we do an experiment with baking soda and vinegar (in a cup) both sealed in a ziplock bag. The bag is masses on a triple beam balance (example 32.7 g). Bag is tilted to allow the vinegar and baking soda to mix.
The students note the signs of chemical reaction and mass the bag again. There is always a 0.3 g – 0.5 g loss of mass. How is this explained? Cheap ziplock bags? Is some of the mass from the endothermic reaction converted?