Which mass is easily forgotten about when trying to prove the law of conservation of mass in a chemical reaction.

water

salt

gas

rock

if you me! : )

Gas

Explanation:

The law of mass conservation states that the total mass of the reactants should be equal to the total mass of the products, that is, the mass should be conserved.

There are specific occasions when students might think that their findings do not follow the law. This is usually the case when some specific gas is evolved in a reaction.

The problem is that when gas evolves, if it's not soluble in a given solution, it escapes it into the surroundings and it seems at first that the mass of the products is actually lower than expected.

We would need to collect the gas evolved and calculate its mass in order to add it to the mass of the remaining products in order to verify the law in such cases.