课程名称：分析化学一 课程性质︰化学系必修 课程教师︰林万寅 开课学院：理学院 开课系所︰理学院 考试日期（年月日）︰2010/11/29 考试时限（分钟）：110+10分钟 是否需发放奖励金：是 试题 Analytical Chemistry November 29, 2010 1 The fractional composition for a certain triprotic acid(H3A) at pH 7.00 are: -4 - 2- 3- -3 H3A=3.323 x 10, H2A=0.3323, HA=0.6647, and A =2.659 x 10. Answer the following questions (A) Find the three acid-dissociation constants(K1,K2,K3)for H3A (6%) (B) Find the pH of 0.010M Na3A solution (5%) (C) Find the pH of 0.010M Na2HA solution (5%) (D) Find the pH of the solution formed by mixing 40.0ml of 0.050M NaH2A and 60.0 ml of 0.040M NaOH (4%) (E) What is the principal species of the H3A-system at (i)pH5.0 (ii)pH9.0(4%) - 2- 3- (F) Find the pH when (i)[H3A]=[H2A] (ii)[H3A]=[HA] (iii)[H3A]=[A] (6%) -11 2 Consider the saturated solution of solid CaF2 (Ksp=3.0 x 10 ) in water. The -4 Ka of HF is 6.67 x 10. Answer the following questions. (A) Write all chemical equilibria and their equilibrium constants expressions.(6%) (B) Write the charge balance equation (2%) (C) Wrute the mass balance equation (2%) (D) Find the solubility of CaF2(s) in water buffered at pH3.0 (5%) 2+ 10 3 The solution of Ca(40.0ml, 0.0500M, bufferedat pH9.0; Kf= 5.0 x 10 ) was titrated with 0.0500M EDTA.(αY=0.054 at pH9.0). Answer the following questions. (A) Calculate the condition formation constant Kf' (2%) (B) Find pCa after addition od 10.0 ml EDTA (4%) (C) Find pCa at the equivalence point (5%) (D) Find pCa after additionof 41.0 ml EDTA (5%) (E) Does pCa (i) before (ii) after the equivalence point depend on pH? Explain(4%) 4 Consider the solution formed by adding excess Mg(OH)2(s) into 0.090M NaCl(aq) Answer the following questions, taking into account the effect of activity coefficient. 2+ - (A) Calculate the activity coefficient of Mg (α=800pm) and OH(α=305pm) using the extended Debye-Huckel equation: 2 __ (4%) -0.51z √μ logγ=________________ __ 1+(α√μ/305) -12 (B)Find the solubility of Mg(OH)2(s)(Ksp=7.1 x 10) in 0.090M NaCl(aq) (4%) (C)Find the pH of the solution (2%) 5Answer the following questions. (A) Describe how to use the method of second-derivative ts locate the equivalence point of an acid-base titration. (5%) (B) (i)Define the isoelectric point (ii) What is the isoelectric point of glycine with pK1=2.35 and pK2=9.77? (5%) (C) Describe fow fraction of dissociation (f) of a weak acid HA is affected by an increase in (i) ionic strength and (ii) size of hydrated anion? (5%) (D) Describe how the titration curve of a weak acid HA is affected by increase in (i) concentration of HA and (ii) pKa of HA? (5%) (E) (i) Define buffer capacity (ii) How to increase the buffer capacity of a buffer solution? (5%) --

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