Passage VI

Figure 1 shows how the H₂O vapor pressure (the pressure exerted by the H₂O vapor in air) varies with the rela­tive humidity (RH) of the air at CTP, which denotes a constant temperature of 25°C and pressure of 101,325 pas­cal (Pa). Figure 2 shows how air density varies with H₂O vapor pressure at CTP.

At CTP, the air above an aqueous solution in a closed container has a constant RH. Figure 3 shows, for 3 com­pound, how the RH of the air at CTP in a closed container varies with the percent by mass, of the compound dissolved in the aqueous solution in the container.

Figure 3 adapted from James G Speight, Labge's Handbook of Chemistry, 16th ed. ©2005 by McGraw-Hill, Inc.