AL chem ...急..請幫幫忙

2007-06-03 10:52 pm

1. A 1 dm^3 solution A is formed by mising equal volumes of 0.2 M ethanoic acid and 0.2 M sodium ethanoate.(ka of ethanoic acid is 1.76*10^-5 mol dm^-3 at 298K)
-calculate the concentrations of each chemical species excluding water which presents in solution A .
- 10 cm^3 of 0.1 M HCL was accidentially poured into 1 dm^3 of solution A .Calculate the change in pH

更新1:

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回答 (2)

魏王將張遼

2007-06-04 5:42 am

✔ 最佳答案

First of all, the solution is prepared by mixing 500 cm3 of ethanoic acid and 500 cm3 of sodium ethanoate, resulting in their initial concentrations being 0.1 M for both.
Then, with reference to the deductions below:

圖片參考：http://i117.photobucket.com/albums/o61/billy_hywung/Jun07/Crazyequil1.jpg

From this, we can see that the change in concentrations to both species are negligible and hence we may state that both species still stay at a concentration of 0.1M.
When 10 cm3 of 0.1M HCl is added,
Increase in no. of moles of ethanoic acid = 0.001
Decrease in no. of moles of ethanoate ions = 0.001
So,
New no. of moles of ethanoic acid = 0.101
New no. of moles of ethanoate ions = 0.099
Then, with reference to the following equation:

圖片參考：http://i117.photobucket.com/albums/o61/billy_hywung/Jun07/Crazyequil2.jpg

We can see that the change in pH is given by:
△pH = log (0.099/0.101)
= -0.009

參考: My chemical knowledge

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Man

2007-06-07 8:41 am

樓主好彩啦, 遇到勁人.

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