One of the most important nitrogen compounds is ammonia. In physical properties, it is a colorless gas with a sharp, suffocating odor (it is the smell of an aqueous solution of ammonium hydroxide NH₃ · H₂O). Gas is highly soluble in water. In an aqueous solution, ammonium is a weak base. It is one of the most important products of the chemical industry.
NH₃ is a good reducer, as in the ammonium molecule, nitrogen has the lowest oxidation state of -3. Many characteristics of ammonia are determined by a pair of single electrons in the nitrogen atom - the addition reactions with ammonia occur due to its presence (this pair of loners is located in the free orbit of Proton H⁺).
How to get ammonia
There are two main practical methods for producing ammonia: one in the laboratory, the other in industry.
Consider ammonia production in industry. The interaction of molecular nitrogen and hydrogen: N₂ + 2H₂ = 2NH₃ (reversible reaction). This method of producing ammonia is called the Haber reaction. For the molecular nitrogen and hydrogen to be reacted, they must be heated to 500 ° C or 932 ° F, an MPA pressure of 25-30 must be created. A porous iron should be present as a catalyst.
Obtaining in the laboratory is a reaction between ammonium chloride and calcium hydroxide: CA (OH) ₂ + 2NH₄Cl = CaCl₂ + 2NH₄OH (as NH₄OH is a very weak compound, it immediately decomposes into gaseous ammonia and water: NH₄OH = NH₃ + H₂O).
Ammonia Oxidation Reaction
They occur with a change in the state of nitrogen oxidation. Since ammonia is a good reducer, it can be used to reduce heavy metals from their oxides.
Reduction of metals: 2NH₃ + 3CuO = 3Cu + N₂ + 3H₂O (when copper (II) oxide is heated in the presence of ammonia, metallic red copper is reduced).
The oxidation of ammonia in the presence of strong oxidizing agents (for example, halogens) occurs according to the equation: 2NH₃ + 3Cl₂ = N₂ + 6HCl (heating is required for this redox reaction). When potassium permanganate acts on ammonia in an alkaline medium, the formation of molecular nitrogen, potassium permanganate and water is observed: 2NH₃ + 6KMnO₄ + 6KOH = 6K₂MnO₄ + N₂ + 6H₂O.
With intense heating (up to 1200 ° C or 2192 ᵒF), ammonia can decompose into simple substances: 2NH₃ = N₂ + 3H₂. At 1000 oC or 1832, ammonia reacts with methane CH 4 : 2CH₄ + 2NH₃ + 3O₂ = 2HCN + 6H₂O (hydrocyanic acid and water). By oxidizing ammonia with sodium hypochlorite, hydrazine ₂₄ can be obtained: 2NH 3 + NaOCl = N 2 H 4 + NaCl + H 2 O
Ammonia combustion and oxygen catalytic oxidation
Oxidation of ammonia by oxygen has certain features. There are two different types of oxidation: catalytic (with catalyst), fast (combustion).
During combustion, a redox reaction occurs, the products of which are molecular nitrogen and water: 4NH3 + 2O2 = 2N2 + 6H2O (the flame is yellow-green, combustion starts at 651 or 103.8 degrees Fahrenheit, since this is the auto-ignition temperature of ammonia). The catalytic oxidation by oxygen also occurs when heated (about 800 ᵒC or 1472 ᵒF), but one of the reaction products is different: 4NH₃ + 5O₂ = 4NO + 6H₂O (in the presence of platinum or iron, manganese, chromium or cobalt oxides, the oxidation products are oxide nitrogen (II) and water).
Consider the uniform oxidation of ammonia by oxygen. Uncontrolled oxidation of the same type of ammonia gas section is a relatively slow reaction. It is not reported in detail, but the lower flammability limit of ammonia-air mixtures at 25 ° C is about 15% in the pressure range of 1-10 bar and decreases with increasing initial temperature of the gas mixture.
If CNH ~ is the mole fraction of NH 3 in the air-ammonia mixture with temperature tmixed (OC), then from the data CNH = 0.15-0 it follows that the flammability limit is low. Therefore, it is reasonable to work with a sufficient margin of safety below the lower flammability limit, as a rule, data on mixing ammonia with air are often far from perfect.
Chemical properties
Consider the contact oxidation of ammonia to nitric oxide. Typical chemical reactions with ammonia without changing the degree of oxidation of nitrogen:
- Reaction with water: NH₃ + H₂O = NH₄OH = NH₄⁺ + he⁻ (the reaction is reversible, since ammonium hydroxide NH₄OH is an unstable compound).
- Reaction with acids to form normal and acid salts: NH₃ + HCl = NH₄Cl (normal ammonium chloride salt is formed); NH₃ + H₂SO₄ = NH₄HSO₄ (in the reaction of ammonia with cold concentrated sulfuric acid, an acid salt of ammonium hydrosulfate is formed); 2NH₃ + H₂SO₄ = (NH₄) ₂SO₄.
- Reactions with salts of heavy metals with the formation of complexes: 2NH₃ + AgCl = [Ag (NH₃) ₂] Cl (silver (I) complex compounds, chloride forms of diamine).
- Reaction with haloalkanes: NH3 + CH3Cl = [CH3NH3] Cl (forms of methylammonium hydrochloride are substituted ammonium ion NH4 =).
- Reaction with alkali metals: 2NH₃ + 2K = 2KNH₂ + H₂ (potassium amide KNH₂ is formed; nitrogen does not change the oxidation state, although the reaction is redox). Addition reactions occur in most cases without changing the oxidation state (all of the above, except the last, are classified by this type).
Conclusion
Ammonia is a popular substance that is actively used in industry. Today it occupies a special place in our life, since we use most of the products of its activities every day. This article will be useful for reading to many who want to know what surrounds us.