Use the density formula to elicit the effect on the density of a gas when the volume changes, the mass remaining constant. Discuss the compression of gas molecules and the effect the compression has on the volume and the pressure. Introduce the concept of diffusion, with molecules moving from areas of greater concentration into areas of less concentration. List the units in use when reporting the pressure a gas exerts.
Define solute and solvent. Indicate solutes may be solids, liquids, or gases. Elicit that solvents may also be any phase.