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[Chem] S2O8^2-離子中 S 的oxidation number

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S2O8^2-離子中 S 的oxidation number

請問 S2O8^2-離子中 S 的oxidation number (氧化數)是多少及怎樣計算?
   

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2x plus (-2)(8) equals -2

2x-16 =-2
2x =14
x =7  這答案肯定是錯的!因為Maximum O.N. = Group No.= 6  (S 是group VI element)

S 的 O.N.一定不會大過 6。

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複製內容到剪貼板
代碼:
General principle:
For each X-X bond, assume no electron transfer.

Let X be more electronegative than Y.
For each X-Y bond, we assume 1 electron is transferred from Y to X.
For each X=Y bond, we assume 2 electron is transferred from Y to X.
and so on
Firstly, you must know the structure of S2O8 2-.

The structure of S2O8 2- and O.N. of O atoms are as follows.
O is more electronegative than S so O gets -1 for each bond.
Note that two of the oxygen atoms also get an electron from the cation. <--I forgot about it earlier.

We can break the O-O bond without affecting our calculation.

Now, let's focus on the left half.
Note that this half carries a charge of -1.
Let x be the O.N. of S.
x+(-2)+(-2)+(-2)+(-1)=-1
x=+6
The O.N. of S is +6.

Similarly for the right half, the O.N. of S is also +6.

[ 本帖最後由 桃子 於 2010-6-15 02:43 PM 編輯 ]

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回覆 #4 桃子 的帖子

認真佩服桃子,連 peroxide linkage 及 S2O8^2- 的electron dot formula 都識!(事實上現在已很少人識了)。不過,智者千慮,必有一失,愚者千慮,必有一得。今次我是愚者,有一得之見。我認為上述两個 S atoms 的O.N.都是 +6,並不是 +5. 理由如下:

你在上面所畫的 electron dot formula 是正確的,不過不要忘了- 2離子的 negative charge -2 有額外的两粒電子加入。你所述的 General principle 亦是十分正確而且很有用!根據上述的
General principle :

For the peroxide linkage,each O-O bond, assume no electron transfer (same electronegativity).
∴ O.N.of both oxygen atoms = 0

Since O is more electronegative than S.
For each S-O bond, we assume 1 electron is transferred from S to O
For each S=O bond, we assume 2 electrons are transferred from S to O.
A total of 6 electrons are are transferred from each S atom,
∴ O.N.of both S atoms =+6

TOP

Sorry!  O.N.of both oxygen atoms =-1 NOT zero! Since 1 electron is transferred to O from S.

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除了 peroxide linkage 的两個 O atoms 的氧化數(O.N.)是 -1 之外,其他的 6 個 O atoms 的氧化數(O.N.)似乎都是 -2,包括電子點式內最上面的那两個 O 原子 (是否和 S 形成 Dative covalent bond?)

TOP

I've made a serious mistake.
There is a -ve charge on O.
Therefore, the O.N. of S should be +6.

Instead of considering the whole left half, we may also consider S alone.
2 electrons are transferred to the O on the left and on the bottom.
1 electron is transferred to the O on the top and on the right.
S loses 6 electrons in total so O.N.=+6.

The O on the top gains 1 electron from S and 1 electron from the cation so O.N.=-2.
The O on the left and on the bottom gain 2 electrons from S so O.N.=-2.
The O in the peroxide linkage gains 1 electron from S and does not gain/lose electron to the adjacent O atom so O.N.=-1.

If you don't want to do any calculation, just remember that peroxide linkage (-O-O-) always have O.N.=-1.

[ 本帖最後由 桃子 於 2010-6-15 04:12 PM 編輯 ]
附件: 您所在的用戶組無法下載或查看附件

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I think the O.N. of S in peroxodisulphate and the O.N. in peroxodisulphuric acid (or peroxyldisulphuric acid) are the SAME! Try to find the O.N.in peroxodisulphuric acid again,
would it be  much simpler & easier?

Peroxydisulfuric is a sulfur oxoacid with the chemical formula H2S2O8.
In structural terms it can be written HO3SOOSO3H. It is one of a group of sulfur oxoacids.

PS:除了 peroxide linkage 的两個 O atoms 的氧化數(O.N.)是 -1 之外,其他的 6 個 O atoms 的氧化數(O.N.)似乎都是 -2,包括電子點式內最上面的那两個 O 原子 ?

在 OF2中,O 的O.N.=+2
在 H2O2中,O 的O.N.=-1
在 O2中,O 的O.N.=0

在 Oxide 及多數含氧的compound/ions 中,O 的O.N.多數=-2

在 sulphate SO4^2-,是否所有 4個 O原子的 O.N.都是 -2?因此我以為
  
"除了 peroxide linkage 的两個 O atoms 的氧化數(O.N.)是 -1 之外,其他的 6 個 O atoms 的氧化數(O.N.)都是 -2,包括電子點式內最上面的那两個 O 原子",不知桃子認為正確嗎?

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>>I think the O.N. of S in peroxodisulphate and the O.N. in peroxodisulphuric acid (or peroxyldisulphuric acid) are the SAME!

That's true.
Acid-base reaction are generally non-redox so acid usually have the same O.N. as conjugate base.

>>"除了 peroxide linkage 的两個 O atoms 的氧化數(O.N.)是 -1 之外,其他的 6 個 O atoms 的氧化數(O.N.)都是 -2,包括電子點式內最上面的那两個 O 原子",不知桃子認為正確嗎?

You are right.

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桃子的附件寫上 "thiosulphate.png"是否寫錯了?
"thiosulphate" 應指 S2O3^2-,現在我們討論的是S2O8^2-,應叫做 "peroxodisulphate or

peroxodisulfate ion, S2O82−,"

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