4.6 Avogadro's Hypothesis

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):

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.