English narration · English + 中文 subtitles burned in · 英語ナレーション・英語＋中文字幕 burning-in
12.1
Why nitrogen is unreactive · ニトロンが不活性である理由
Syllabus · シラバス
English
explain the lack of reactivity of nitrogen, with reference to triple bond strength and lack of polarity
describe and explain: (a) the basicity of ammonia, using the Brønsted–Lowry theory (b) the structure of the ammonium ion and its formation by an acid–base reaction (c) the displacement of ammonia from ammonium salts by an acid–base reaction
state and explain the natural and man-made occurrences of oxides of nitrogen and their catalytic removal from the exhaust gases of internal combustion engines
understand that atmospheric oxides of nitrogen ($\text{NO}$ and $\text{NO}_2$) can react with unburned hydrocarbons to form peroxyacetyl nitrate, PAN, which is a component of photochemical smog
describe the role of $\text{NO}$ and $\text{NO}_2$ in the formation of acid rain both directly and in their catalytic role in the oxidation of atmospheric sulfur dioxide
Ammonia has three bonding pairs and one lone pair — the lone pair pushes the bonds down into a pyramidal shape (about 107°). · アンモニアには結合電子対が3つ、非共有電子対が1つある——非共有電子対が結合を下へ押し下げ、三角錐形（約107°）を形成する。
12.1
Ammonia and the ammonium ion · アンモニアとアンモニウムイオン
English
Basicity of ammonia
The basicity 碱性 of ammonia (its ability to act as a base) comes from the lone pair 孤对电子 of electrons on the nitrogen atom. Using the Brønsted–Lowry theory, ammonia is a base because this lone pair can accept a proton 质子 ($\text{H}^+$):
When the lone pair forms a bond to $\text{H}^+$, it makes the ammonium ion 铵离子, $\text{NH}_4^+$. Because both shared electrons came from the nitrogen, this new bond is a coordinate bond 配位键. The ion has four identical N–H bonds and a tetrahedral shape.
Displacement of ammonia from its salts
If you warm an ammonium salt with a base (such as sodium hydroxide), you push out ammonia gas. This is an acid–base displacement 置换:
In sunlight, $\text{NO}$ and $\text{NO}_2$ react with unburned hydrocarbons to form peroxyacetyl nitrate (PAN). PAN is a harmful part of photochemical smog 光化学烟雾, the brown haze seen over busy cities.
Acid rain
The oxides of nitrogen also help make acid rain 酸雨 in two ways:
directly: $\text{NO}_2$ dissolves in rain to form nitric acid.
as a catalyst: $\text{NO}_2$ speeds up the oxidation of atmospheric sulfur dioxide 二氧化硫 ($\text{SO}_2$) into $\text{SO}_3$, which then forms sulfuric acid in the rain.
Worked example. A white solid is warmed with aqueous $\text{NaOH}$, and a gas is released that turns damp red litmus blue. Identify the gas and the ion in the solid, and explain the reaction. The only common gas that turns damp red litmus blue is ammonia, $\text{NH}_3$, so the solid contains the ammonium ion, $\text{NH}_4^{+}$. The hydroxide ion is the stronger base, so it takes the proton back from the ammonium ion:
This is the standard test for $\text{NH}_4^{+}$. Always say the litmus is damp: the ammonia must dissolve in the water before it can show its basicity, so dry litmus would give no colour change at all.
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