Ammonia preparation method

Industrially, hydrogen and nitrogen react to produce ammonia
.

The laboratory prepares ammonia by co-heating ammonium salt and strong base or hydrolysis of metal nitrides

Ammonia is a colorless gas at room temperature and pressure with a pungent odor
.

NH ₃ has greater polarity and can form hydrogen bonds with water, so ammonia is extremely soluble in water (1 volume of water at 20°C can dissolve 775 volumes of ammonia)

The molecular structure of ammonia is shown in Figure 12-1
.

From the structure and composition of nitrogen molecules, it can be known that ammonia molecules can undergo coordination reactions, oxidation reactions, and substitution reactions (including ammonolysis reactions)

Figure 12-1 Schematic diagram of nitrogen molecular structure

1.

Coordination reaction (addition reaction)

The lone electron pair of N in the ammonia molecule adducts with compounds or ions with empty orbitals to form adducts or complexes, such as H ₃ N→BF ₃ , [Ag(NH ₃ ) ₂ ]+, [Cu(NH ₃ ) ₄ ] ₂ ⁺ and the like
.

Due to the formation of easily soluble complexes, AgCl and Cu(OH) ₂ can be dissolved in ammonia

2.

Substitution reaction

The hydrogen in the ammonia molecule can be substituted in turn to generate the corresponding derivative
.

One hydrogen in the ammonia molecule is replaced to generate an amino compound

The substitution of 2 hydrogens in the ammonia molecule generates imino compounds, such as CaNH; the substitution of 3 hydrogens in the ammonia molecule generates nitrides, such as NCl ₃ and so on
.

The liquid ammonia solution of sodium metal slowly decomposes to liberate hydrogen, and a white sodium amide (NaNH ₂ ) solid is obtained
.

3.

Chlorolysis reaction

Even ammonia from the ammonia from the constant although smaller than water, but can also occur hydrolysis reaction similar to the reaction solution, NH2 _.

3
NH2 dissociation produced ₂ ^- in combination with the cationic
.
From the perspective of the reaction product, the ammonolysis reaction can be regarded as a substitution reaction
.

4.
Oxidation reaction

The oxidation number of N in NH ₃ molecules is -3, and N can lose electrons and be oxidized under certain conditions
.

Under the action of platinum catalyst, ammonia can be oxidized to nitric oxide , which is an important reaction for the production of nitric acid
.

5.
Ammonium salt

(1) The formation of ammonium salt
.
Ammonia reacts with acid to form ammonium salt
.
E.
g

Ammonium salts are easily soluble in water and are strong electrolytes
.
Ammonia is a weak base, and ammonium salt dissolves in water and undergoes a hydrolysis reaction
.
The aqueous solution of ammonium salt of strong acid radical is acidic, such as NH ₄ CI and NH ₄ NO ₃ ; while the aqueous solution of ammonium acetate (NH ₄ Ac) is nearly neutral
.

Some acid radicals are strongly alkaline after hydrolysis, and their ammonium salts often cannot be precipitated by evaporation and concentration of aqueous solutions, such as (NH ₄ ) ₂ S, (NH ₄ ) ₂ CO ₃ , (NH ₄ ) ₃ PO _4, etc.
, these ammonium salts There are no commercially available reagents, and there are no solutions of these ammonium salts in the laboratory
.
The simple calculation results show that when the concentration of NH ₄ ⁺ and NH _{3 in the} solution is the same, the concentration of HCO ₃ ^- is more than 10 times higher than that of CO ₃ ² -, and the concentration of HS ^- is more than 100 times higher than that of S ₂ ^-
.
The experimental results also show that (NH ₄ ) ₂ S and (NH ₄ ) ₂ CO ₃ cannot be precipitated from the aqueous solution , but only NH ₄ HS and NH ₄ can be obtained.
HCO ₃ crystals
.

(2) Decomposition of ammonium salt
.
The ammonium salt has poor thermal stability, and the decomposition temperature of the normal salt of the ammonium salt of a polybasic weak acid is often lower than that of the acid salt
.
For example, (NH ₄ )2S decomposition temperature is 0℃, NH ₄ HS decomposition temperature is 25℃, (NH ₄ ) ₂ CO ₃ decomposition temperature is 58℃, NH ₄ HCO ₃ decomposition temperature is 107℃, (NH ₄ )2HPO _{4 The} decomposition temperature is 155℃, the decomposition temperature of (NH ₄ ) ₂ SO ₄ is 280℃, and the decomposition temperature of NH ₄ C1 is 520℃
.

The ammonium salt of a volatile non-oxidizing acid, ammonia and acid volatilize and escape after thermal decomposition
.
E.
g

Non-volatile non-oxidizing acid ammonium salt, ammonia volatilizes and escapes after thermal decomposition
.
E.
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The ammonium ion of the oxidizing acid is oxidized during the thermal decomposition process
.
The decomposition product is a gas and emits a lot of heat, and it often explodes
.
E.
g