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我們來看看其他

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組分原子或分子的氧化態

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那麽假設有氧化鎂(MgO)

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氧化鎂MgO

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我用不同的顏色表示氧

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00:00:16,580 --> 00:00:18,970
那麽它們的氧化態是什麽？

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00:00:18,980 --> 00:00:20,190
你可能已經知道了

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00:00:20,200 --> 00:00:21,570
但還是來看看元素周期表吧

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因爲再熟悉一下也無傷大雅

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呐 鎂(Mg)

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鎂有兩個價電子

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它是第二主族元素

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它很樂意抛棄這兩個電子

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而氧(O) 地球人都知道

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它是電負度最強的原子之一

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它電負度太強了

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以致於“氧化”都是以氧命名的

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然後我們知道氧喜歡得到兩個電子

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所以這簡直是天作之合

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這玩意兒想丟掉兩個電子

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而這玩意兒想得到兩個

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那麽接下來會怎麽樣？

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鎂會失去兩個電子

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它本來是中性的

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那麽假設它會帶上2單位正電荷

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然後 氧就帶上2單位負電荷了

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因爲它拿走那兩個電子了

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所以在氧化鎂分子裏

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鎂的氧化態是+2

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而氧的氧化態是-2

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我們現在來做難一點的

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假設是氫氧化鎂 Mg(OH)2

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氫氧根是(OH)2

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這裡氫氧根有兩個

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好啦 我的思路還是… 嗯

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鎂很樂意失去它的電子 兩個電子

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這樣它就會帶上正電

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這種假設下它的價態是正的

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那麽我的思路是

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嘿 鎂是+2

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我先寫下來

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記住啦 如果這是個電中和合物

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爲了使一切和諧

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全部價態加起來要等於0

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那我們來看看行不行

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呐 氧

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我武斷認爲它的氧化態

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應該是-2

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那我寫下來吧

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是-2

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而氫 如果它和氧成鍵…

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記住 這情況下 氫會先和氧

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成鍵

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然後一起和鎂成鍵

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所以氫和氧成鍵

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氫 如果它和鎂成鍵

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你可能會覺得 噢

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可能氫會拿走那兩個電子

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然後它就變成負價的了

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不過氫和氧成鍵的時候

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它是放棄電子那個

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它只有一個電子可以放棄

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所以它是+1價

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嗯… 開始你可能會說 好了

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我把氧化態都加起來

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+2-2就是0 還有+1

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我就得到氧化態是+1

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Sal 這沒道理啊

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這是個電中和合物啊

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你要留意的是 噢 錯了

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你可是有兩個氫氧根的啊

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那你應該先算出

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氫氧根的總氧化態

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那是-2+1

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所以整個氫氧根

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總共是-1價

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然而你有兩個 對吧？

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你這有兩個氫氧根

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所以每個氫氧根對整個化合物的

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氧化態的貢獻是-1

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而這有兩個

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所以這是-2 再加上鎂的+2

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全部加起來是0

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搞定了

85
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接下來 我想順便做點別的

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我想重新回到某些問題上

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不過我想順便講講

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一些術語

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因爲我已經某程度上用了“氧化態”、

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“被氧化” 或者“被還原”

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然而 我們講了那麽多

92
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水解離的問題…

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那 2份水

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反應處於平衡

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生成1份的H3O+和OH-

96
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很明顯 這些都在溶液裏

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現在 先看水分子

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這裡水的各個氧化態是多少？

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呐 上集我們做過這個了

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氧的氧化態是-2

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因爲它從兩個氫那裏勾搭了兩個電子

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每個氫都貢獻了1個電子

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所以氫的氧化態是+1

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那麽我們來看這個分子

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都加起來

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因爲有兩個+1的氫

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所以是+2

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+2加上氧的-2 等於0

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水是中和合物

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那這邊 氧化態又是多少？

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也就是其中一個氫離開了它的水分子

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然後粘上了另一個水分子

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但它沒帶走電子

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所以它把電子留這裡了

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那麽這個氧的氧化態還是-2

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而這個氫還是+1

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所以你要用-2+1

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就得到-1

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這次就沒問題

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因爲氫氧根的確是帶負電的

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那這個的價態怎麽樣？

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每個氫都是+1

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然後這個氧是-2

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那麽如果你看整個離子的電荷

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3個氫分別是+1 那就是+3

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只是加起來了

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還有-2

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所以就是+3-2 所以整個離子是

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+1價的 而事實正是如此

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現在 我想問你們

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有哪個原子的氧化態變了嗎？

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這兒全部的氫…

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或者說這兩份水的

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或者是兩個水分子的

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那我就有4個氫了

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對吧？ 而它們的氧化態都是+1

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等式右邊 有4個氫

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全部的氧化態都是+1

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那麽它們都是+1價 這個反應裏…

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無論是哪個反應方向

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氫都沒有被氧化

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它的氧化態沒有變

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可能氫在前面形成水的反應裏

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被氧化了

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不過這個反應裏 它沒有

146
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同理 氧…

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有兩個氧分子 是原子 這兒

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每個都是-2價

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這裡有兩個氧原子

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每個都是-2價

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對於這個反應 至少

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從氧化態看 沒有電子轉手

153
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所以這不是一個氧化還原反應

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我會在下集裏詳細地講

155
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不過我要講清楚

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這兒沒東西被氧化或還原

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因爲它們的氧化態保持不變

158
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因爲有時我會說 嘿 看

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鎂的氧化態是+2

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而氧的氧化態是-2

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鎂被氧化了

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它失去了兩個電子

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而氧被還原

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它得到了兩個電子

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那麽我指的是某個生成它的反應

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但是也不總是這樣的

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你可以假設一個

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不必發生的反應

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但是鎂的氧化態

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一定是+2

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而氧的氧化態

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或者說氧化態 是-2

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不過我相信我說鎂被氧化時

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你懂我的意思

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其實就是 鎂通過失去兩個電子

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從一個中性的鎂

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變成了一個帶正電的鎂

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所以它被氧化了

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接下來 我們來做些難題

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過氧化氫(H2O2)

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我已經說過幾次了

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氧是趨向於變成-2價的

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這個是-1

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我想你看出特點了 這些元素都是+1

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氫是+1或-1

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這些都是+2

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我想你明白這規律了

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這就是你希望得到或失去電子

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你會說 呐

190
00:08:16,060 --> 00:08:19,690
水的氧通常是-2價的

191
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所以這應該…

192
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好啦

193
00:08:22,260 --> 00:08:25,190
氫是+1 因爲它和水成鍵

194
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而氧是-2

195
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如果你這樣想 馬上就會碰到難題了

196
00:08:31,310 --> 00:08:32,750
這是個中性分子…

197
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嗯 兩個氫就是+2

198
00:08:35,430 --> 00:08:36,880
兩個-2的氧

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是-4

200
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所以整個氧的氧化態

201
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最終是-4

202
00:08:41,530 --> 00:08:42,860
肯定不是這樣的

203
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因爲這個不帶電

204
00:08:44,140 --> 00:08:45,790
這兒就有難題了

205
00:08:45,800 --> 00:08:47,480
而有難題是因爲…

206
00:08:47,490 --> 00:08:50,410
如果你仔細觀察過氧化氫的結構

207
00:08:50,440 --> 00:08:53,550
氧之間是成鍵的

208
00:08:53,570 --> 00:08:55,170
這就是“過氧”

209
00:08:55,180 --> 00:08:59,630
而每個氧又和氫成鍵

210
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所以這時

211
00:09:01,730 --> 00:09:03,960
特別是第一年的化學課上

212
00:09:03,970 --> 00:09:07,370
過氧根 尤其是過氧化氫

213
00:09:07,390 --> 00:09:08,840
趨向於當個特例

214
00:09:08,860 --> 00:09:11,390
也有別的 但這個是個特例

215
00:09:11,410 --> 00:09:15,350
這時氧的氧化態的確不是-2

216
00:09:15,370 --> 00:09:17,090
我們來看這個並算算

217
00:09:17,100 --> 00:09:18,600
過氧化氫的氧的

218
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氧化態是多少

219
00:09:20,090 --> 00:09:23,030
這時 在氫氧鍵中

220
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氧會吸電子

221
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而氫會失去電子

222
00:09:27,520 --> 00:09:29,000
那麽氫是+1

223
00:09:29,020 --> 00:09:30,040
另一邊也同理

224
00:09:30,060 --> 00:09:33,160
氧 至少在這個鍵上 得到+1價

225
00:09:33,180 --> 00:09:34,410
因爲它會得到一個電子

226
00:09:34,420 --> 00:09:36,710
那氧之間的鍵呢？

227
00:09:36,720 --> 00:09:39,660
嗯… 沒理由一個氧會

228
00:09:39,670 --> 00:09:41,230
吸走另一個氧的電子

229
00:09:41,250 --> 00:09:43,850
所以這不會對它的氧化態的值

230
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有任何影響

231
00:09:45,010 --> 00:09:48,000
因此這情況下 這個氧的氧化態是-1

232
00:09:48,010 --> 00:09:52,770
這個氧也是-1

233
00:09:52,780 --> 00:09:59,400
所以每個氫的氧化態是+1

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00:09:59,420 --> 00:10:03,070
我們說過氧離子中氧的氧化態是-1

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00:10:03,090 --> 00:10:05,740
所以總的值是0

236
00:10:05,750 --> 00:10:08,790
2乘+1 加上2乘-1 等於0

237
00:10:08,810 --> 00:10:10,680
這是個特例

238
00:10:10,690 --> 00:10:12,970
不過熟悉它很重要

239
00:10:12,980 --> 00:10:14,330
我們再做一個

240
00:10:14,340 --> 00:10:15,840
碳酸鐵(Ⅲ)

241
00:10:15,850 --> 00:10:17,690
現在第一次…

242
00:10:17,700 --> 00:10:19,970
我記得我們第一次遇到碳酸鐵(Ⅲ)

243
00:10:19,980 --> 00:10:21,220
你可能會想 呃

244
00:10:21,230 --> 00:10:22,960
爲什麽這叫碳酸鐵(Ⅲ)

245
00:10:22,970 --> 00:10:25,250
而這兒只有兩個鐵分子

246
00:10:25,260 --> 00:10:26,430
兩個鐵原子？

247
00:10:26,440 --> 00:10:27,820
你馬上就會學到了

248
00:10:27,830 --> 00:10:29,410
我們來看看氧化態

249
00:10:29,430 --> 00:10:31,410
氧的

250
00:10:31,420 --> 00:10:35,870
氧的氧化態 一般是-2

251
00:10:35,890 --> 00:10:38,210
是-2

252
00:10:38,220 --> 00:10:40,650
現在 如果碳(C)連在氧(O)上…

253
00:10:40,670 --> 00:10:42,540
我們看元素周期表吧

254
00:10:42,550 --> 00:10:45,680
碳和氧成鍵

255
00:10:45,700 --> 00:10:48,510
碳怎麽變都行

256
00:10:48,520 --> 00:10:51,270
碳 有時它喜歡貢獻電子

257
00:10:51,300 --> 00:10:52,870
有時它希望得到電子

258
00:10:52,890 --> 00:10:55,100
而碳和氧成鍵是

259
00:10:55,110 --> 00:10:58,110
這裡可是個電子狂

260
00:10:58,130 --> 00:11:01,140
如果一定要說誰奪走了電子

261
00:11:01,150 --> 00:11:02,670
答案會是氧

262
00:11:02,680 --> 00:11:03,890
對吧？

263
00:11:03,900 --> 00:11:06,860
所以碳會貢獻它的電子

264
00:11:06,870 --> 00:11:09,760
不過碳能拿出幾個電子呢？

265
00:11:09,780 --> 00:11:11,470
嗯 看看

266
00:11:11,480 --> 00:11:14,990
它有1 2 3 4個價電子

267
00:11:15,010 --> 00:11:16,070
所以它真正最多能

268
00:11:16,080 --> 00:11:18,560
貢獻4個價電子

269
00:11:18,570 --> 00:11:21,450
回到碳酸根

270
00:11:21,460 --> 00:11:26,110
所以碳最多能

271
00:11:26,120 --> 00:11:29,370
貢獻4個價電子

272
00:11:29,390 --> 00:11:32,400
那麽碳酸根的總的氧化態

273
00:11:32,420 --> 00:11:33,870
是多少？

274
00:11:33,880 --> 00:11:36,390
CO3的

275
00:11:36,400 --> 00:11:38,770
所以這是+4價

276
00:11:38,790 --> 00:11:40,290
因爲它只有4個了

277
00:11:40,300 --> 00:11:42,680
如果它和氧成鍵 它就會貢獻全部

278
00:11:42,690 --> 00:11:43,880
氧是個超級電子狂

279
00:11:43,890 --> 00:11:46,270
每個氧是-2

280
00:11:46,280 --> 00:11:48,790
我們來想想

281
00:11:48,800 --> 00:11:54,130
我有+4 加【譯者注：口誤】 3乘-2

282
00:11:54,150 --> 00:11:55,210
對吧？

283
00:11:55,260 --> 00:11:57,220
我有3個氧原子

284
00:11:57,240 --> 00:12:00,350
所以是4-6等於-2

285
00:12:00,370 --> 00:12:02,850
所以我們可以把整個碳酸根

286
00:12:02,860 --> 00:12:05,790
看作是-2價的

287
00:12:05,810 --> 00:12:10,640
那麽 如果整個碳酸根是-2

288
00:12:10,660 --> 00:12:14,370
它對整個分子的氧化態的

289
00:12:14,390 --> 00:12:16,940
貢獻是…

290
00:12:16,950 --> 00:12:18,730
這個碳酸根

291
00:12:18,740 --> 00:12:20,630
我們有3個碳酸根

292
00:12:20,640 --> 00:12:22,630
每個的貢獻是-2

293
00:12:22,640 --> 00:12:24,680
所以這有-6的貢獻值

294
00:12:24,700 --> 00:12:28,360
如果這是-6 並且這是個中性分子

295
00:12:28,380 --> 00:12:32,210
那麽我們兩個鐵就必須要

296
00:12:32,220 --> 00:12:35,370
貢獻+6價

297
00:12:35,380 --> 00:12:36,820
因爲全部加起來是0

298
00:12:36,830 --> 00:12:40,160
如果兩個鐵加起來

299
00:12:40,180 --> 00:12:43,380
貢獻了+6價

300
00:12:43,400 --> 00:12:46,410
那麽每個鐵就是+3價

301
00:12:46,420 --> 00:12:49,600
或者 在我們的推理裏 如果這成立

302
00:12:49,620 --> 00:12:52,650
至少每個鐵會有3個電子

303
00:12:52,670 --> 00:12:54,800
樂意和碳酸根待一起

304
00:12:54,840 --> 00:12:58,120
那爲什麽這叫碳酸鐵(Ⅲ)咧？

305
00:12:58,120 --> 00:13:00,400
我想現在你就懂了

306
00:13:00,420 --> 00:13:04,870
因爲這是鐵價態爲3的情況

307
00:13:04,880 --> 00:13:06,070
鐵… 很多金屬

308
00:13:06,090 --> 00:13:07,550
特別是過渡金屬

309
00:13:07,560 --> 00:13:09,560
能有幾種價態

310
00:13:09,570 --> 00:13:11,290
如果你有碳酸鐵(Ⅲ)

311
00:13:11,300 --> 00:13:12,680
實際上就表示

312
00:13:12,690 --> 00:13:14,330
它的價態是3

313
00:13:14,340 --> 00:13:17,810
或者說分子裏鐵的氧化態

314
00:13:17,820 --> 00:13:19,600
會是+3

315
00:13:19,610 --> 00:13:21,940
現在 我們再做一個

316
00:13:21,960 --> 00:13:23,030
這很有趣

317
00:13:23,050 --> 00:13:24,200
醋酸(乙酸)

318
00:13:24,210 --> 00:13:25,560
我想這是第一次

319
00:13:25,570 --> 00:13:29,990
我秀出醋酸的結構式

320
00:13:30,010 --> 00:13:33,160
我不會講太多有機化學的內容

321
00:13:33,170 --> 00:13:37,620
不過我們會看到不同的價態

322
00:13:37,640 --> 00:13:39,200
或者說氧化態

323
00:13:39,210 --> 00:13:41,560
[少一句]

324
00:13:41,570 --> 00:13:43,280
有時候你會看到這個形式

325
00:13:43,290 --> 00:13:44,600
你會覺得OK

326
00:13:44,610 --> 00:13:48,050
氧 每個氧會是-2

327
00:13:48,070 --> 00:13:50,890
[少一句]

328
00:13:50,920 --> 00:13:53,270
每個氫會是+1

329
00:13:53,280 --> 00:13:56,560
[少一句]

330
00:13:56,570 --> 00:13:57,600
目前的情況如何？

331
00:13:57,630 --> 00:14:01,520
這些氧一共就是-4

332
00:14:01,540 --> 00:14:03,290
至於氫

333
00:14:03,300 --> 00:14:08,930
這裡是+3 然後這還有+1

334
00:14:08,950 --> 00:14:12,070
你把它們都加起來就是0 你會想 噢

335
00:14:12,090 --> 00:14:14,890
所以碳就沒氧化態咯

336
00:14:14,900 --> 00:14:16,780
它們的氧化態一定是0

337
00:14:16,790 --> 00:14:20,480
因爲只看氫和氧

338
00:14:20,490 --> 00:14:23,040
我們已經是0了

339
00:14:23,050 --> 00:14:25,670
那麽我們來看是否確實如此

340
00:14:25,680 --> 00:14:28,770
所以如果碳和氫成鍵

341
00:14:28,780 --> 00:14:30,230
誰更吸電子？

342
00:14:30,240 --> 00:14:34,670
碳氫鍵

343
00:14:34,680 --> 00:14:37,160
越往右邊 電負度越強

344
00:14:37,170 --> 00:14:39,330
碳的電負度更強

345
00:14:39,350 --> 00:14:42,690
比起氫 碳更喜歡保留電子

346
00:14:42,700 --> 00:14:43,800
或者說貪圖電子

347
00:14:43,810 --> 00:14:45,470
所以在氧化還原角度看

348
00:14:45,480 --> 00:14:46,980
氫失電子

349
00:14:46,990 --> 00:14:50,600
它是個共價鍵 不過當然

350
00:14:50,620 --> 00:14:51,870
我們知道討論氧化態的時候

351
00:14:51,880 --> 00:14:53,260
就假裝是電價鍵

352
00:14:53,280 --> 00:14:56,620
所以這時 你的氫將會

353
00:14:56,630 --> 00:14:58,140
失電子

354
00:14:58,160 --> 00:15:00,170
所以它們的氧化態分別是+1

355
00:15:00,190 --> 00:15:02,940
這和我們目前知道的一致

356
00:15:02,950 --> 00:15:04,740
不過其實這是另一回事

357
00:15:04,760 --> 00:15:06,680
我做這裡這練習的時候

358
00:15:06,710 --> 00:15:07,750
我第一時間假設氫

359
00:15:07,760 --> 00:15:10,810
氧化態爲+1

360
00:15:10,820 --> 00:15:11,850
我這樣是因爲 噢

361
00:15:11,860 --> 00:15:13,620
分子裏的剩下的只有碳和氧

362
00:15:13,630 --> 00:15:15,800
它們的電負度都更大

363
00:15:15,810 --> 00:15:17,950
所以氫會變成它的+1價

364
00:15:17,960 --> 00:15:19,670
如果這裡是

365
00:15:19,680 --> 00:15:21,500
鹼金屬 或者鹼土金屬

366
00:15:21,520 --> 00:15:22,910
我就不會那麽肯定了

367
00:15:22,930 --> 00:15:24,540
我會說 氫可能會奪走它們的電子

368
00:15:24,550 --> 00:15:26,470
好啦

369
00:15:26,490 --> 00:15:30,270
所以這些都會給碳一個電子

370
00:15:30,290 --> 00:15:32,270
因此光從氫身上

371
00:15:32,290 --> 00:15:39,200
碳就得到-3價了

372
00:15:39,220 --> 00:15:41,450
這些失電子

373
00:15:41,460 --> 00:15:43,170
而這家夥得到了3電子

374
00:15:43,190 --> 00:15:44,620
所以它的價態減少3

375
00:15:44,630 --> 00:15:47,450
碳碳鍵 嗯 沒理由

376
00:15:47,470 --> 00:15:49,620
一個碳可以從另一個碳上奪走電子

377
00:15:49,630 --> 00:15:51,400
碳碳生而平等

378
00:15:51,410 --> 00:15:53,770
所以沒有電子轉移

379
00:15:53,800 --> 00:15:56,120
所以這碳被氧化了3價

380
00:15:56,140 --> 00:15:57,490
現在這邊又怎麽樣呢？

381
00:15:57,500 --> 00:16:00,130
已知這氫的氧化態

382
00:16:00,140 --> 00:16:02,750
會是+1

383
00:16:02,770 --> 00:16:04,830
它會把電子給這個氧

384
00:16:04,850 --> 00:16:07,880
而這個氧 就跟大部分氧一樣

385
00:16:07,890 --> 00:16:09,680
需要吸兩個電子

386
00:16:09,690 --> 00:16:12,960
一個來自碳 一個來自氫

387
00:16:12,970 --> 00:16:15,800
所以氧的氧化態是-2

388
00:16:15,810 --> 00:16:19,100
這個氧也需要吸走兩個電子

389
00:16:19,110 --> 00:16:20,700
這情況下 它們兩個都會

390
00:16:20,720 --> 00:16:22,100
來自這個橙色的碳

391
00:16:22,120 --> 00:16:24,490
那麽它的氧化態就是-2

392
00:16:24,510 --> 00:16:26,720
所以這個碳的氧化態是多少？

393
00:16:26,730 --> 00:16:30,190
它給了兩個電子這兒家夥

394
00:16:30,200 --> 00:16:35,350
然後有給了1個電子下面這個氧

395
00:16:35,360 --> 00:16:37,700
提醒一下 這家夥得到一個碳的電子

396
00:16:37,710 --> 00:16:38,830
和一個氫的

397
00:16:38,840 --> 00:16:41,600
這裡沒了1個 那裏沒了兩個

398
00:16:41,610 --> 00:16:43,390
它失去了3個電子

399
00:16:43,410 --> 00:16:47,570
所以事實上 它是+3價的

400
00:16:47,590 --> 00:16:52,010
因此結果是醋酸的碳的

401
00:16:52,020 --> 00:16:54,990
平均氧化態是0

402
00:16:55,010 --> 00:16:56,990
因爲如果你取-3和+3的平均值

403
00:16:57,000 --> 00:16:58,300
會得到0

404
00:16:58,320 --> 00:17:00,520
這就是爲什麽我說 噢可能它們是0

405
00:17:00,530 --> 00:17:03,180
但如果你真的寫出它們的氧化態

406
00:17:03,200 --> 00:17:07,300
這個綠色的碳 氧化態-3

407
00:17:07,310 --> 00:17:10,020
而這個橙色的C 橙色碳

408
00:17:10,030 --> 00:17:12,640
氧化態是+3

409
00:17:12,660 --> 00:17:14,050
如果你懂了這個例子

410
00:17:14,070 --> 00:17:16,060
我並不覺得這太複雜

411
00:17:16,080 --> 00:17:21,880
你會變成氧化態迷的

412
00:17:21,890 --> 00:17:23,750
那麽我想你都準備好了

413
00:17:23,760 --> 00:17:25,150
下集 我們會開始研究

414
00:17:25,160 --> 00:17:28,150
氧化還原反應