Imagine that you have two identical flasks, one containing chlorine gas and the other containing argon at the same temperature and pressure. How can you tell which is which without opening them?

Key Concepts

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). Chlorine gas (Cl2) has a molar mass of approximately 70.9 g/mol, while argon (Ar) has a molar mass of about 39.9 g/mol. This difference in molar mass can affect the density of the gases, which can be used to distinguish between them.

Density of Gases

The density of a gas is defined as its mass per unit volume and is influenced by its molar mass and the conditions of temperature and pressure. Under the same conditions, a gas with a higher molar mass will have a higher density. By comparing the densities of chlorine and argon, one can determine which gas is in which flask without opening them.

Diffusion Rate

Diffusion is the process by which gas molecules spread from areas of high concentration to areas of low concentration. According to Graham's law of effusion, lighter gases diffuse faster than heavier gases. Since argon is lighter than chlorine, if there is a way to observe the rate of diffusion, it can help identify which gas is in each flask.