1. Relate equilibrium to solubility . Partially soluble salts (e.g., AgCl, PbI 2 , or PbCl 2 ) can be used to explore the equilibrium aspects of solubility and to determine values for K sp . Two approaches can be used. (1) Put a weighed excess of the salt in a measured amount of water; stir; filter the undissolved salt from the liquid, dry and weigh the undissolved salt. From the difference in masses the quantity of dissolved salt can be determined. (2) Precipitate the salt from soluble ions (e.g., AgCl from AgNO 3 and NaCl). Filter the precipitate, dry and weigh. Compare the mass with the stoichiometrically expected mass. The difference is the mass of dissolved salt.
2. Relate equilibrium to buffer action . The pH of various buffered systems can be studied. The acetic acid/acetate system can be studied by varying the relative concentrations of the two species.
3. Quantitative treatment of equilibrium . Two straightforward methods can be used to derive equilibrium constants. (1) Measure the pH of a serial dilution of acetic acid from 0.1 M to 0.0001 M. Use a pH meter (inexpensive battery-operated ones can be obtained from Fisher Scientific 13-300-51). (2) Compare the relative conductivity of 0.01 M HCl (assume 100% dissociation) with the same concentration of HC 2 H 3 O 2 . By assuming the percent dissociation is related to the relative conductivity, the K a value of acetic acid can be determined. An inexpensive battery-operated conductivity apparatus can be obtained from Fisher Scientific (09-331-4). It comes in two ranges and is called a dissolved solids tester. You may need two ranges to do this test (100-19,900 mS and 10-1,990 mS).
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