研究所、轉學考(插大)-物化分析題庫下載題庫

10. Which of the following description is correct? (4%)
(A) The solubility product constant (Ksp) of aluminum hydroxide (Al(OH)3) is 3 ×10-34; the Ksp of cadmium sulfide (CdS) is 1× 10-27. Based on this information, we know that Al(OH)3 is less soluble than CdS in pure water.
(B) A glass of aqueous solution (100 mL) contains [Ca²⁺] = 2.13✖10^-4 M, [F^-] = 4.26✖ 10 ^-4 M, and 0. 781 g of insoluble Caf₂ solid. Based on this information, we can estimate the Ksp of Caf2 to be ~3.9 x 10-11
(C) Even through the same chemical can sometimes exist in more than one crystalline form, e.g., CaCO₃ can be both calcite and aragonite, they are always equally soluble.
(D) The pK_a1and pK_a2 of methionine are 2.28 and 9.21. Based on this information, we know that methionine has the best buffering power (capacity) at pH 5.75 (the mid-point between the two pKa values).
(E) The hydrogen cation concentration ([H⁺]) of a pH 6.5 solution is 5.0 ✖10^-7 M.