Calcium Benzoate: a. A sample of saturated CaBz_2 solution is at equilibrium: Ca
ID: 507963 • Letter: C
Question
Calcium Benzoate: a. A sample of saturated CaBz_2 solution is at equilibrium: CaBz_2(s) Ca^2+(aq) + 2B_z(aq) The initially prepared concentrations are [Ca^2+]_i = a and [B_z]_i = b. This sample is allowed to saturate, and then the remaining solid is filtered out. As determined by titration, the final benzoate ion concentration in solution is [Bz^-]_f = c. What is the solubility product of CaBz_2, in terms of a, b and c? b. In our lab experiment, the CaBz_2 solution is saturated at equilibrium before titration. Why must the CaBz_2 solution be saturated?Explanation / Answer
a. According to the stoichiometry of the equilibrium, the final concentration of Calcium ion will be half of the final concentration of benzoate in the solution. It is given that the final concentration of benzoate in solution is 'c'. Therefore, the final concentration of Calcium ions is 'c/2'. Thus the solubility product of calcium benzoate is c2*c/2= c3/2.
b. As Calcium benzoate is only sparingly soluble in water, the concentration of calcium and benzoate ions in solution will be very less, which will cause difficulty in determining the end point of the titration. If we use a saturated solution of calcium benzoate , the dynamic equilibrium will provide a good supply of ions for titration. Through the titration, if we determine the final concentration of one of the ions, we can calculate the final concentration of the other ion as described in section 'a' above, as well as the solubility product of the sparingly soluble salt.