is compensated by the difference in height of, hence in gravitational pressure
in, both compartments. Incidentally, this implies that by application of a
pressure to a solution that is higher than its osmotic pressure, solvent can be
removed from the solution, thereby increasing the concentration of the
solute; this is called reversed osmosis.
The osmotic pressure of an ideally dilute aqueous solution is given by
P¼ 55 ; 510 RTlnx 1 & 55 ; 510 RTx 2 & 103 m 2 RT ð 2 : 17 Þwhere the factor 55,510 represents the number of moles of water in a m^3.
Sincem 2 ¼n=V, wheren¼the number of moles in the volumeV, Eq. (2.17)
FIGURE2.4 Measurement of osmotic pressureðPÞ. Solvent and solution are
separated by a membrane that lets the solvent pass but not the solute. The
small circles denote the solute molecules (or particles). h¼heightðmÞ, r¼
mass densityð 103 kg?m^3 for water) and g¼acceleration due to gravity
ð 9 :81 m?s^2 Þ.