推 jasonfghx :你是化學系的? 12/21 08:49
課程名稱︰分析化學一
課程性質︰必帶
課程教師︰林萬寅
開課學院：理學院
開課系所︰化學系
考試日期（年月日）︰2010/11/08
考試時限（分鐘）：20(的樣子)
是否需發放獎勵金：是
（如未明確表示，則不予發放）
Department: Name: Registered number: （←→表可逆符號）
1.
Write the charge balance equation, mass balance equation and all chemical
equibria for the saturated aqueous solution of Ca3(PO4)2.
Neglect the hydrolysis of Ca2+ 20%
ANS
Charge balance: 2[Ca2+] + [H+] = [H2PO4–] + 2[HPO42–] + 3[PO43–] + [OH–]
Mass balance: 2 [Ca2+] = 3([H3PO4] + [H2PO4–] + [HPO42–] + [PO43–])
Ca3(PO4)2(s) ←→ 3 Ca2+ +2 PO43-
PO43- + H2O ←→ HPO42- + OH-
HPO42- + H2O ←→ H2PO4- + OH-
H2PO4- + H2O ←→ H3PO4 + OH-
2 H2O ←→ H3O+ OH- (or H2O←→H+ + OH-)
2.
Find the pH of 1.0*10^-7 M HCl solution.
ANS:
Charge balance (or mass balance): [H+] = [OH-] + [Cl-]
[Cl-] = 1.0*10-7M; activity coefficients ≒ 1 for H+ & OH-
Kw =[H+][OH-]=([Cl-]+[OH-])[OH-]=1.0*10^-14
[OH-]=6.18*10^-8 M ; [H]=1.62*10^-7 M; pH=6.79
3.
Find the solubility of Ag2CrO4(s) (Ksp=1.2*10^-12) in water with an ionic
strength of 0.1M, knowing that the activity coefficients for Ag+ and CrO42-
are 0.75 and 0.36, respectively. Neglect the hydrolysis of Ag+ and CrO42-
ANS:
2
Ksp=[Ag+]^2[CrO4 2-](γAg+)*(γCrO4 2-)
[CrO4 2-]=S ; [Ag+]=2S
Ksp=4S^3*0.75*0.75*0.36=1.2*10^-12
S=1.1*10^-4M
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