Ammonia. Aqueous solution
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|Ammonia is one of the most important nitrogen compounds.
Nitrogen is part of proteins and nucleic acids and is one of the components that form the basis of life. Therefore, it was important to learn how to synthesize chemical compounds with nitrogen. First used electricity, but this method proved to be very expensive. A simpler way is a chemical reaction of nitrogen in the air with hydrogen to form the chemical compound ammonia!
In the industry getting of ammonia related with its synthesis from simple substances. As already noted, the source of nitrogen is air, and hydrogen is got from water.
3H2 + N2 -> 2NH3 + Q
The reaction of the synthesis of ammoniais reversible, therefore it is important to choose the conditions that has yield of ammonia greatest in the chemical reaction. This reaction is conducted at high pressure (15 to 100 MPa). During the reaction the volume of gases (hydrogen and nitrogen) is reduced in 2 times, so the high pressure can increase the amount of generated ammonia. Catalyst in such a reaction is sponge iron. It is interesting to note, that sponge iron acts as a catalyst only at temperatures above 5000C. But when the temperature increase the molecule of ammonia destroyed into hydrogen and nitrogen. To avoid the destruction of the molecules, when the mixture of gases passes through the sponge iron the formed ammonia immediately cool! Moreover if it a strong cool the ammonia becomes a liquid.
Getting of ammonia in the laboratory, produced from a mixture of solid ammonium chloride (NH4Cl) and slaked lime. When heated ammonia intensely excreted .
2NH4Cl + Ca(OH)2 -> CaCl2 + 2NH3 + 2H2O
Properties of ammonia
Ammonia at standard conditions - a gas with a pungent and unpleasant smell. Ammonia is toxic! At 20 0C 700 l of ammonia dissolves in water. The resulting solution is called the ammonia water. Because of this the solubility of ammonia can not be collected and kept over the water.
Ammonia is an active reducing agent. It has this property because of presence nitrogen atoms that have an oxidation number "-3". Restorative properties of nitrogen are observed at combustion of ammonia in air. The most stable oxidation number of nitrogen is 0, the result of this reaction is free nitrogen.
If use catalysts (platinum Pt and chromium oxide Cr2O3) in combustion reaction, we get nitric oxide.
4NH3 + 5 O2 -> 4NO + 6H2O
Ammonia can recover the metals from their oxides. So the reaction with copper oxide is used to produce nitrogen.
2NH3 + 3CuO -> 3 Cu + N2 +3 H2O
Ammonia has properties of alkali. When dissolved it in water is formed ion of ammonium and hydroxide ion. The connection NH4OH - does not exist! Therefore, the formula ofammonia water better to write as a formula of ammonia!
Alkali properties of ammonia also appear in reactions with acids.
NH3 + HCl -> NH4Cl (ammonium chloride)
NH3 + HNO3 ->NH4NO3 (ammonium nitrate)
Ammonia reacts with organic substances. For example, an artificial amino acid are got with reaction of ammonia and A-chlorine substituted carboxylic acids. Released in the reaction hydrogen chloride (HCl - gas) is associated with excess of ammonia and form ammonium chloride NH4Cl.
Many complex compounds contain ammonia as a ligand. Ammonia solution of silver oxide, that is used for the detection of aldehydes, is a complex compound - hydroxydopamine silver.
Ag2O + 4NH3 + H2O ->2[Ag(NH3)2]OH
Ammonium salts - solid crystalline substances without colors. Almost all of them are dissolved in water and have same properties that have a known salt of metal. They react with alkalis, ammonia is excreted.
NH4Cl + KOH -> KCl + NH3 + H2O
In this case, if in addition to use indicator paper, this reaction can be used as a qualitative reaction for salts of ammonium. Ammonium salts react with other salts, and acids. For example,
(NH4)2SO4 + BaCl2 -> BaSO4 + 2NH4Cl
(NH4)2CO3 + 2HCl2 -> 2NH4Cl + CO2 + H2O
Ammonium salts is unstable to heat. Some of them, chloride of ammonium, - evaporate when heated, others, such as ammonium nitrite, - decompose.
NH4Cl -> NH3 + HCl
NH4NO2 -> N2 + 2H2O
The last chemical reaction - the decomposition of ammonium nitrite is used in chemical laboratories to produce pure nitrogen.
Ammonia is a weak alkali, so the salts are formed with ammonia in aqueous solution are hydrolyzed. There are large number or hydronium ions in solutions of these salts, so the reaction of ammonium salts is acidic!
NH4+ + H2O -> NH3 + H3O+
Use of ammonia and its salts based on the specific properties. Ammonia is a raw material for the production of nitrogen containing substances, and as salts used as a mineral fertilizer. An aqueous solution of ammonia can be bought in pharmacies with the name of ammonia.
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