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