Chem easy Q2~

Question

Comment on the following sentence which consists of two statements joined by the word "because". "Ammonia is a reducing agent" because " an ammonia molecule has a lone pair of electrons."
Concerntrated nitric acid 係唔係唔會同copper react

Answer 1

The statement「Ammonia is a reducing agent」is true.
The most famous reaction that ammonia acts as a reducing agent is the catalytic oxidation of ammonia :
4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g)
In the reaction, ammonia is oxidized as the oxidation number of N is increased from -3 to +2. On the other hand, O2 is reduced by NH3 as the oxidation number of O is decreased from 0 to -2.

The statement「An ammonia molecule has a lone pair of electron」is also true.
The electronic structure below shows the electronic diagram of ammonia, in which a lone pair of electron is shown.

圖片參考：http://www.notre-dame-college.edu.hk/~zt-leunghmc/nh3.jpg

However, the reducing power of ammonia is NOT because of the existence of lone pair of electrons in ammonia molecule. The correct reason is that the oxidation number of N in ammonia is -3, which is the lowest among all nitrogen compounds..

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At room temperature, concentrated nitric acid reacts with copper to give a blue solution of copper(II) nitrate and a brown gas of nitrogen dioxide.
Cu(s) + 4H+(aq) + 2NO3-(aq) → Cu2+(aq) + 2H2­O(l) + 2NO2(g)