[試題] 99上 林萬寅 分析化學一 第二次期中考
課程名稱：分析化學一
課程性質︰化學系必修
課程教師︰林萬寅
開課學院：理學院
開課系所︰理學院
考試日期（年月日）︰2010/11/29
考試時限（分鐘）：110+10分鐘
是否需發放獎勵金：是
試題
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)
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(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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