有chem問題f.5

其實，這一類是復分解反應(double decomposition reaction):-
例如離子化合物的水溶液反應:
AB + CD ------->AD + CB
如果產物(AD 或 BC) 任何一個是"水、沉澱或氣體"，會在水溶液中失去離子性的話，那AD 和BC再不會變回成 AB 和 CD，即逆反應不發生，反應是可行的
例如(以下方程式不配平):
第一題:
A的答案 NH4Cl + NaOH = NaCl + NH3 + H2O，NH3是氨氣，這是氣體，加上有水生成
C的答案 Cu(NO3)2 + NaOH = Cu(OH)2 + NaNO3，Cu(OH)2 是沉澱
D的答案 ZnSO4 + NaOH = Zn(OH)2 + Na2SO4，Zn(OH)2是沉澱
第二題:
1的答案和第一題A一樣
2的答案 CuSO4 + NaOH = Cu(OH)2 + Na2SO4，Cu(OH)2 是沉澱
3的答案 CH3COOH + NaOH = CH3COO^- Na^+ + H2O，有水生成

否則:
正如第一題的B，K2CO3 + NaOH = Na2CO3 + KOH， 全部水溶，沒沉澱、氣體和水產生。即逆反應亦可發生，反應是不可行的。

This examinationa is a test for the positive-charged ions. By adding sodium hydroxide solution, precipitates will form as most hydroxides are insoluble in water.
1. A and B will have no reaction with NaOH and remains colourless, but C and D will react with NaOH to form insoluble hydroxide precipitates.
Cu(NO3)2 + 2NaOH --> 2NaNO3 + Cu(OH)2
ZnSO4 + 2NaOH -- > Na2SO4 + Zn(OH)2
Copper(II) hydroxide is a reddish brown precipitates and zinc hydroxide is a cloudy white precipitates.
2. Copper(II) sulphate and ethanoic acid can react with NaOH but ammonium chloride does not.
CuSO4 + 2NaOH --> Cu(OH)2 + Na2SO4
Brownish precipitates will form.
CH3COOH + NaOH --> CH3COONa + H2O
Neutralization occurs, no observation will be seen
If you want to know any change or reaction in chemistry, first thing you have to know is what is property of that chemical and what test is going to do. Like Sodium Hydroxide, it is well known a strong alkaline that can have neutralization with acid, but together its hydroxide properties mostly insoluble in water which is a good test to check the presence of positive-charged ion in chemical. Right?