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[問題] chem pH concept question

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chem pH concept question

我想問下如果有一隻 alkali (NaOH) 加落隻 acid (HCl) 到 , 畫幅 pH against volume of NaOH added 既 graph , 點解 pH 先係慢慢升之後突然升得好快再之後變返升得好慢 ?
如果 plot temperature against volume of NaOH added , temp 又係無啦啦升得好快 , 個 principal 其實係咪一樣
THX
   

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呢個我諗要用計數解釋:
consider the titration of 25 cm3 1M HCl with 1M NaOH
To deduce the titration curve, we should calculate the pH of the solution when 0-50 cm3 1M NaOH have been added.
To make it simpler, we may just calculate the pH of solution when 24.9cm3, 25 cm3 and 25.1 cm3 of  1M NaOH have been added. (because the change in pH is not significant at the initiation and the end of the titration)
(assume that NaOH and HCl are fully ionised)
1. when 24.9cm3 1M NaOH have been added
no. of mol of H+ remaining=0.025X1-0.0249X1=0.0001 mol
[H+]=0.0001/(0.0249+0.025)=2.02X10^-3 M
pH=2.69

2. When 25 cm3 1M NaOH have been added
[H+]= 1X10^-7M(hydrolysis of water)
pH=7.00

3. When 25.1 cm3 1M NaOH have been added
no. of mol of OH- remaining =0.0001 mol
[OH-]=0.0001/0.0501=1.996X10^-3 M
pOH=2.699, pH=11.3

so, we have
Volume of NaOH added/cm3  24.9          25.0            25.1
pH                                                  2.69            7.0           11.3
所以中間咪直線lol

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回覆 2# rickylok 的帖子

其實有無得explain點解會咁
btw explaination AL 係咪 out c

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係咪OUT C真係好難講,
AL CHEM冇一樣嘢係100% OUT C
解真係唔知點解到,計數算解到……
如果strong acid + weak alkali
咪可以當佢salt + acid有buffering effect lo,所以pH變得慢
但係strong acid + strong alkali都係咁,小第就解唔到啦……
唯有等高手賜教 (應該係Mathematics/quantitative嘅嘢pH=-log[H+])

[ 本帖最後由 rickylok 於 2012-4-21 07:27 PM 編輯 ]

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