Chapter 14, Problem 115FP

The laboratory device pictured on the following page is called a desiccators. It can be used to maintain a constant relative humidity within an enclosure The material(s) used to control the relative humidity are placed in the bottom compartment and the substance being subjected to a controlled relative humidity is placed on the platform in the container.

a If the material n the bottom compartment is a saturated solution of NaCl(aq) in contact with NaCI(s), what will be the approximate relative humidity in the container at a temperature of 20 'C Obtain the solubility of NaCl from Figure 14-10 D and vapor pressure data for water from Table 12.5; use the definition of Raoult’s law from page 660 and that of relative humidity from Focus On 6-1: Earth's Atmosphere: assume that the NaCI is completely dissociated into its ions
b If the material placed on the platform is dry ${\text{CaCl}}_{\text{2}}\cdot {\text{6H}}_{\text{2}}\text{O}\left(\text{s}\right)$ , will the solid deliquesce Explain. [Hint: Recall the discussion on pages 664 -665]
c. To maintain ${\text{CaCl}}_{\text{2}}\cdot {\text{6H}}_{\text{2}}\text{O}\left(\text{s}\right)$ in the dry state in a deliquescence should the substance in the saturated solution in the bottom compartment be one with a high or a low water solubility? Explain.