19. Gas A is composed of diatomic molecules (two atoms to a molecule) of a pure element. Gas B is composed of monoatomic molecules (one atom to a molecule) of another pure element. Gas A has three times the mass of an equal volume of gas B at the same temperature and pressure. How do the atomic masses of elements A and B compare?

The atomic mass of element A is 1.5 times greater than the atomic mass of element B.

Gas A = A2 (g)

Gas B = B (g)

3 / 2 = 1.5 (Lets say Gas A has a mass of 3 units, Gas B then has a mass of 1 unit. There are 2 atoms per molecule in Gas A so we divide the mass between the two.)

1 / 1 = 1 (Since Gas B has a mass of 1 unit and there is 1 atom per molecule, the unit of mass is attributed only to the 1 atom.)

Element A = 1.5 units

Element B = 1 units