Question

A 250mL Erlenmeyer flask weighing 55g contains 5g of sodium bicarbonate. To this, an excess, 15g, of acetic acid is added to the flask. While swirling, many bubbles are present. Finally, you stop swirling the flask, and the bubbles stop. You then place this flask on an analytical balance. The mass registers 73g.
How does this final mass compare with the value expected according to the Law of Conservation of mass?

Why do you believe that this comparison exists?

State the Law of Conservation of Mass. Do these results break this law? Why?

What changes, if any, could be made to the procedures in this experiment to allow a closer comparison to what the Law of Conservation would expect?

Answer 1

First, let us revise the Law of Conservation of Mass. It states that the total mass in an isolated system remains constant.

The results obtained are not in accordance with this law, because the total mass before the reaction was 75 grams and after the reaction was 73 grams. This seems that there was some mass lost.

This discrepancy is due to the fact that a gas was produced due to the reaction, namely carbon dioxide, and was lost from the beaker into the surroundings.

In order to get results in accordance to the law of conservation of mass, we may simply isolate the system (beaker and reaction mixture) from the surroundings further by putting a cork or some other instrument to seal the beaker.<span />