One of the most important nitrogen compounds is ammonia. According to its physical properties, it is a colorless gas with a sharp, suffocating odor (this is the smell of an aqueous solution of ammonium hydroxide NH₃·H₂O). The gas is highly soluble in water. In 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 -3. Many characteristics of ammonia are determined by a pair of single electrons in the nitrogen atom - addition reactions with ammonia occur due to its presence (this pair of singles is located on the free orbit of the Proton H⁺).
How to get ammonia
There are two main practical methods for obtaining ammonia: one in the laboratory, the other in industry.
Consider the production of ammonia in industry. Interaction of molecular nitrogen and hydrogen: N₂ + 2H₂=2NH₃(reversible reaction). This method of obtaining ammonia is called the Haber reaction. For molecular nitrogen and hydrogen to react, they must be heated to 500 ᵒC or 932 ᵒF, an MPA pressure of 25-30 must be built up. Porous iron must be present as a catalyst.
Receiving 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 proceed with a change in the oxidation state of nitrogen. Since ammonia is a good reducer, it can be used to reduce heavy metals from their oxides.
Metal Reduction: 2NH₃ + 3CuO=3Cu + N₂ + 3H₂O (When copper(II) oxide is heated in the presence of ammonia, red copper metal decreases).
Oxidation of ammonia in the presence of strong oxidizing agents (for example, halogens) occurs according to the equation: 2NH₃ + 3Cl₂=N₂ + 6HCl (this redox reaction requires heating). When exposed to potassium permanganate on ammonia in an alkaline medium, the formation of molecular nitrogen, potassium permanganate and water is observed: 2NH₃ + 6KMnO₄+ 6KOH=6K₂MnO₄+ N₂ + 6H₂O.
When heated intensively (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 CH4: 2CH₄ + 2NH₃ + 3O₂=2HCN + 6H₂O (hydrocyanic acid and water). By oxidizing ammonia with sodium hypochlorite, hydrazine H₂X₄ canget: 2NH3 + NaOCl=N2H4 + NaCl + H 2O
Combustion of ammonia and its catalytic oxidation with oxygen
Oxidation of ammonia with oxygen has certain features. There are two different types of oxidation: catalytic (with a catalyst), fast (burning).
When burning, a redox reaction occurs, the products of which are molecular nitrogen and water: 4NH3 + 2O2=2N2 + 6H2O self-ignition of ammonia). Catalytic oxidation with 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 oxides of iron, manganese, chromium or cob alt as a catalyst, the oxidation products are oxide nitrogen (II) and water).
Consider the homogeneous oxidation of ammonia with oxygen. Uncontrolled monotonous oxidation of an ammonia gas site 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 as the initial temperature of the gas mixture increases.
If CNH~ is the molar fraction of NH3 in an air-ammonia mixture with a 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 limitflammability, as a rule, data on mixing ammonia with air are often far from perfect.
Consider the contact oxidation of ammonia to nitric oxide. Typical chemical reactions with ammonia without changing the nitrogen oxidation state:
- Reaction with water: NH₃ + H₂O=NH₄OH=NH₄⁺ + he⁻ (the reaction is reversible because ammonium hydroxide NH₄OH is an unstable compound).
- Reaction with acids to form normal and acidic s alts: NH₃ + HCl=NH₄Cl (normal ammonium chloride s alt is formed); 2NH₃ + H₂SO₄=(NH₄)₂SO₄.
- Reactions with s alts of heavy metals to form complexes: 2NH₃ + AgCl=[Ag(NH₃)₂]Cl (complex silver compounds (I) diamine chloride forms).
- Reaction with haloalkanes: NH3 + CH3Cl=[CH3NH3]Cl (methylammonium hydrochloride forms are the substituted ammonium ion NH4=).
- Reaction with alkali metals: 2NH₃ + 2K=2KNH₂ + H₂ (forms potassium amide KNH₂; 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).
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 its products every day. This article will be a useful read for many who want to know about what surrounds us.