## Chemical Concept Demonstrated

• The relative weights of gases

## Demonstration

• Using a syringe and a top-loading balance, calculate the weight of 50mL volume of different gases.

## Observations

Each gas sample is the same size. However, the samples all weigh different amounts. In the video, the values were as follows (gases appear in the order given below):

 Gas Mass 1. Vacuum (Calibration) .000 g 2. Oxygen .055/.054 g 3. Hydrogen .011 g 4. Carbon Dioxide .088 g 5. Sulfur Hexafluoride .263 g

## Explanation

Heavier gas samples weigh more than lighter ones. A gas sample cannot weigh more in this experiment by a change of volume, so the change must be related to the mass of the gas particles themselves.

Had the atomic/molecular weights of the gases been plotted against their experimental weights, it would have proven to be a straight line. There is a direct correlation between the atomic/molecular mass and the mass of a fixed sample (Avogadro's hypothesis, more or less). Using this hypothesis, a gas sample's atomic/molecular mass can be determined by simply weighing a fixed amount against a predetermined linear relationship.

## Contributors

• Dr. George Bodner