Ideally should the mass of copper at the start and finish of the exepriment be the same?
what law of chemistry applies to this situation?
as a practical matter, why would the two masses of copper metal be different?

Explanation:

Ideally the two masses of copper should be the same, this is explained by the Lavoisier's law or the law  of conservation of mass. Lavoisier states that mass is neither created nor destroyed by chemichal reactions in an isolated enviroment.

But, as a practical matter, the masses should be a little different beacuse always a fraction of mass becomes energy.

answer: c. the experiment shows that the red substance experienced a chemical change.

explanation: chemical change is the change in which chemical composition of the substance changes. physical change is the change in which there is no change in chemical composition.

chemical changes are accompanied by following changes:

a) precipitate formation

b) energy is released or absorbed

c) formation of bubbles

d) change in color

as it is given that the red color has disappeared and there is production of gas, it means the red substance has undergone a chemical change.

e