Analytical chemistry

2014-08-02 8:22 pm

For each of the following pairs of substances ,suggest a chemical test to distinguish one substance from the other and state expected observations.
----Ammonium chloride and potassium chloride

Problem solving
4 labels have come off four reagent bottles
Pb(NO3)2, ZnCl2,Mg(NO3)2,NaCl
Describe the tests that you would do to identify which bottle contained which substabce.State also your expected observations.
這些都是依題目打的，可能文法上我會有不明白，可是我會等大家答了我以後才在補充問題的。謝謝！

回答 (5)

不用客氣

2014-08-02 10:59 pm

✔ 最佳答案

1.
Add separately each of the two substances to dilute sodium hydroxide solution in a test tube. Warm each mixture.
Ammonium chloride : A colourless gas is given off which turns moist red litmus paper to blue.
Potassium chloride : No observable change.

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2.
If the substances are in solid state, dissolve separately each of the four substances in distilled water to give a solution.

Put separately 2 cm³ of each of the four solutions in a test tube, and add dilute sodium sulphate solution.
Only Pb(NO3)2 solutions gives a white precipitate.
The other three solutions give no observable change.

Put separately 2 cm³ of each of the rest three solutions in a test tube, and add dilute sodium hydroxide solution, firstly dropwise and then in excess.
NaCl solution gives no observable change.
ZnCl2 and Mg(NO3)2 solutions give white precipitates.
For ZnCl2 solution, the precipitate re-dissolves to give a colourless solution.
For Mg(NO3)2 solution, the precipitate remains unchanged when excess sodium hydroxide solution is added.

參考: 不用客氣

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用戶26240

2015-03-02 8:56 pm

一個好的答案，獲得三個「非正面」的評價。是這裡不是尊重知識的地方，還是來的是沒有知識的人？

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