12-4 to find the solubility (mol/L) of R3NH Br in a solution maintained at pH 9.
ID: 1045417 • Letter: 1
Question
12-4 to find the solubility (mol/L) of R3NH Br in a solution maintained at pH 9.50. Use the equilibria Ksp = 4.0 × 10-8 Ka 2.3 x 10-9 12-33. At neutral pH, CaSO,(s) dissolves in water to give Ca", So? , and the ion pair, CaSO,(a?). Bisulfate (HSO4) Ca has an "acid dissociation" constant of has a pKa of 2.0. pKa 12.70 for the reaction Ka (a) It is observed that the solubility of CasO4(s) is nearly constant over the pH range 3 to 8.5. Explain why. (b) What do you expect to happen to the solubility at low pH (below 3) and at high pH (above 12)? 12-34. (a) Ignoring activity coefficients, find the concentra- tions of Ag', CN, and HCNaq) in a saturated solution ofExplanation / Answer
a) It is observed that the solubility of CaSO4 is almost constant in pH range of 3 to 8.5 ,because at low pH more complex of HSO4- and at high pH more complex of CaOH ,which both would allowed more dissolution ( dissolution rate depend on concentration of Ca2+, SO4-, concentration of ions in solution.
One more reason is that the solubility of CaSO4 in water is almost not affected by pH . Its depend on change in Temperature and concentration of ions in solution and other factors .
(b) Solubility of CaSO4 is 12% enhance at pH 2.5 and also observed that increase in solubility at pH 8.5 ,but after pH 12 the solubility of CaSO4 slightly decreases , not so much affected by pH.
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