Question

A student added 3 gms one substance in a beaker and then added 4 gms of another substance. A chemical reaction took place in the uncovered beaker, after the reaction the beaker weighed 5 gms which of the following is the best explanation?
A Some of the mass of the reactants was lost as heat and evaporated into the air.
B. The reaction produce a gas as a product.
C. Some of the reactantants were destroyed as when the chemicals were added.

Answer 1

Answer:

B. The reaction produce a gas as a product.

Explanation:

According to the law of conservation of mass, the total mass of reactants must be equal to the total mass of products because mass is neither created nor destroyed in a chemical reaction.

The total mass of the reactants is 7 grams. The total mass of the products and the beaker is 5 grams. This means that the mass of products is less than the mass of reactants.

The only plausible explanation for this is that the reaction produced a gaseous product which escaped because the system is an open system thereby leading to a  lesser measured mass of products since mass can not be created nor destroyed.