Question

A student wants to demonstrate the law of conservation of mass during a chemical reaction.

They find the mass of their initial reactants to be 52 grams. They conduct the reaction in a
beaker, and notice bubbles being produced in the reaction. At the conclusion of the reaction,
they find the mass of the products to be 46 grams. Based on their observations, which of the
following most likely explains the apparent change in mass?
A. The student made a mistake measuring the reactants.
B. The student conducted the reaction in an open beaker, which allowed one of the products, a
gas, to escape.
C. The student accidentally conducted a nuclear reaction in the beaker, and actually did destroy
matter by converting it into energy.
D. Conservation of mass is only a theory, and may be wrong.

Answer 1

The apparent change in mass during the student's experiment is most likely because the reaction occurred in an open beaker, allowing gas to escape, which is consistent with the law of conservation of mass.

Step-by-step explanation:

When a student conducts a chemical reaction in an open beaker and observes a decrease in mass from 52 grams to 46 grams, with the production of bubbles, it is most likely due to the escape of a gas. This phenomenon can be explained by the law of conservation of mass, which states that mass is not created or destroyed during a chemical reaction. Instead, it is simply changed from one form to another. Therefore, if the reaction is conducted in an open system where gas can escape, the mass of the products measured will be less than the original reactants, even though the total mass including the escaped gas would remain the same.

For example, baking bread releases gas and loses mass, but the combined mass of the bread and the escaped gas is the same as the original dough. When magnesium burns in the air to form magnesium oxide, the mass of magnesium oxide is greater than the original magnesium due to the combination with oxygen from the air. Antoine Lavoisier proved the law by showing that there was no change in total mass when a sealed flask containing a chemical reaction was weighed before and after the reaction.

Answer 2

B. The student conducted the reaction in an open beaker, which allowed one of the products, a gas, to escape.

Step-by-step explanation:

Based on the law of conservation of mass, matter is neither created nor destroyed during the course of a chemical reaction.

By this premise, the mass of reactants and products must remain the same during the course of a reaction.

• Here we find that this is not the case.
• The mass of the product reported is less than the mass of the reactants.
• The problem is that the mass of the gas bubbles produced during the course of this reaction was not accounted for.
• This leaves a mass deficit already