作者theye (Momiji)
看板Chemistry
標題[學習] 一題mass balance
時間Sun Nov 7 13:30:13 2010
最近分析化學學到以系統方法處理化學平衡，
其中，對於寫出mass(material) balance則是感到困惑。
‧"the quantity of all species in a solution containing a particular atom
(or group of atoms) must equal the amount of that atom (or group)
delivered to the solution."
‧"it really refers to conservation of atoms, not to mass."
以上兩段話皆出自於"Quantitative Chemical Analysis, D. C. Harris, page151"
e.g. CaCl2 in water if species are Ca2+, Cl-, CaCl+, CaOH+
then MB: 2[total calcium] = [total chloride]
=> 2{[Ca2+] + [CaCl-] + [CaOH-]} = {[Cl-] + [CaCl+]}
以上這例子，寫出MB不是件難事。
然而，
e.g. ....find the concentrations of the major species in 0.10M NaClO4
saturated with Mn(OH)2. ......
Consider just the following chemistry:
Mn(OH)2 (s) <=> Mn2+ + 2OH- Ksp
Mn2+ + OH- <=> MnOH+ K1
H2O <=> H+ + OH- Kw
寫出相關方程式、CB、MB...
卡在MB不曉得是哪兩種物種的平衡，於是翻了後面的solution
出現了一個令我不解的等式
[OH-] + [MnOH+] = 2{[Mn2+] + [MnOH-]} + [H+]
species species
containing OH- containing Mn2+
為什麼要加上[H+]呢?
又mass balance的準則到底何在呢?
翻回前段的介紹再讀幾遍，仍沒想通...
所以來請教板上的各位。謝謝噢！
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◆ From: 140.118.234.20
1F：推 yutsao:因為OH-的產生除了Mn之外還會有水的解離 11/07 13:41
2F：→ yutsao:其實是[OH-](from Mn) + [MnOH+] = 2{[Mn2+] + [MnOH-]} 11/07 13:42
3F：→ jui8048:承上，加上水的解離就變成[OH-]total+[MnOH]=...+[H+](略) 11/07 14:19
※ 編輯: theye 來自: 140.118.234.20 (11/07 19:28)