A piece of steel wool (very thin steel fibers, made mostly of iron) is placed on a small scale inside an air-tight container. The air-tight container is placed on a larger outer scale. Electric current is passed through the steel wool. The small scale inside the container allows you to measure the changes of mass of the steel wool. The air-tight container makes sure that the air surrounding the steel wool can not escape, nor can more air enter the container. The outer scale lets you measure the mass of the entire system: container, steel wool, and air.

In this scenario, the mass reading on the smaller, inside scale increases, however, the mass on the larger outside scale does not increase. Let's look at if different gases were placed in the container.

If the air tight container were filled with carbon dioxide gas, what would the scale readings do (would they both increase, decrease, stay the same, etc)?

If the air tight container were filled with pure oxygen gas, what would the scale readings do (would they both increase, decrease, stay the same, etc)?

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2. Steel wool and small scale are placed inside air-tight container 3. Air-tight container sits on large scale 6184.6 Steel wool sits on small scale inside air-tight container