Ammonia NH3

AMMONIA
Mar 15, 2023
AMMONIA [NH3] 
Ammonia is an hydride of nitrogen formed when an ammonium salt is heated with a non-volatile base. In nature, ammonia is produced when nitrogenous matter decays in the absence of air by the action of heat or putrifying bacteria.

Laboratory preparation of Ammonia  
Ammonia is prepared in the laboratory by heating a mixture of powdered ammonium salt and a strong alkali.
NH4Cl(s) +Ca(OH)2(s) ----> CaCl2(s) + 2NH3(g) + 2H2O(g)
(NH4)2SO4(s) + Ca(OH)2(s) ----> CaSO4(s) +2NH3(g) + 2H2O(g)
Calcium hydroxide is prefered because it is cheap and not deliquescent. The ammonia gas evolved on heating is dried by passing it through calcium oxide and then collected by upward delivery.
For the fact that the gas is alkaline, the usual drying agent like Concentrated tetraoxosulphate (vi) acid and calcium chloride are not used for drying it, as they react with the gas:
2NH3(g) + H2SO4(aq) ----> (NH4)2SO4(s)
 4NH3(g) + CaCl2(s) -----> CaCl2.4NH3(s)

Preparation of Ammonia
Ammonia is also conveniently prepared in the laboratory by the hydrolysis of nitrides
Li3N(s) + 3H2O(l) ----> 3LiOH(aq) + NH3(g) 
Ca3N2(s) + 6H2O(l) -----> 3Ca(OH)2(aq) + 3NH3(g)
Industrial preparation of Ammonia 
(Haber Process)
Ammonia is obtained industrially by the Haber process, which is based on the direct combination of nitrogen and hydrogen.
 N2(g) + 3H2(g) === 2NH3(g)
Since the reaction is reversible, special conditions of reaction are required for the optimum yield of ammonia. The process involves mixing nitrogen and 
hydrogen in the volume ratio of 1:3 at a relatively high pressure of about 200 atmosphere and passed over a catalyst of finely divided iron mixed with alumina at a temperature of 450"C.
The ammonia produced is liquefied by cooling and stored for further use. 
The Haber Process)
Facts about the Haber Process.
Raw materials:
 * Air (for nitrogen) 
 * Natural gas (to make hydrogen)
 * Steam (to make hydrogen and to generate high pressures).
Conditions 
 * Temperature about 450oC 
 * Pressure - about 200 atmosphere
 * Catalyst- finely divided iron mixed with alumina. Energy from the process is also re-cycled are exothermic. The energy they give out is used to heat 
reaction vessels and to make steam.
Physical properties of Ammonia 
 1. Ammonia is a colourless gas with a characteristic pungent smell. 
2. It is less dense than air. 
3. It is an alkaline gas, therefore it turns moist red litmus paper blue. 
4. Ammonia is very soluble in water. The solubility is due to the readiness with which it forms hydrogen bond with water to give aqueous ammonia: NH3.H2O. Aqueous ammonia ionizes slightly to produce ammonium ion, NH4+and hydroxide ion: OH- 
NH3(g) + H2O(l) === NH3.H2O(aq)
 NH3.H2O(aq) === NH4+(aq) + OH-(aq)
On warming, aqueous ammonia decomposes readily to liberate ammonia gas. 
5. In large quantities ammonia is poisonous.
6. It is easily liquefied into a colourless liquid at ordinary temperature.
7. Ammonia has a bioling point of -77.8°C and melting point of -34.4°C. 
Chemical properties of Ammonia 
1. Reaction with oxygen: 
Ammonia burns readily in oxygen to form water vapour and nitrogen.
4NH3(g) + 3O2(g) -----> 6H2O(g) + 2N2(g) 
 In the presence of heated platinum catalyst, ammonia reacts with excess oxygen to produce nitrogen (ii) oxide and water.
4NH3(g) + 5O2(g) ----> 4NO(g) + 6H2O(l) 
2. Ammonia as a reducing agent 
(i) With copper (ii) oxide: 
 Ammonia is not a strong reducing agent. It reduces heated copper (ii) oxide to copper while itself is oxidized to water and nitrogen.
 3CuO + 2NH3(g) ---->3Cu(s) + 3H2O(l) + N2(g)
 (ii) With chlorine: 
 In the presence of excess ammonia, chlorine is first reduced to hydrogen chloride and nitrogen.
2NH3(g) + 3Cl2(g) -----> 6HCl(g) + N2(g)
The hydrogen chloride then reacts with the excess ammonia to produce dense white fumes of ammonium chloride.
6NH3(g) + 6HCl(g) ----> 6NH4Cl(s).
The overall reaction is as follows: 
3Cl2(g) + 8NH3(g) ---> 6NH4Cl(s) +N2(g)
If chlorine is in excess, nitrogen trichloride, an explosive and oily liquid is formed.
 NH3(g) + 3Cl2(g) ----> NCl3(l) + 3HCI(g)
 3. Reaction with carbon (iv) oxide Ammonia reacts with carbon(iv)0xide at 150°C and a high pressure of 150 atmosphere to produce urea, an important 
organiC compound.
2NH3(g) + CO2(g) ----> (NH2)2CO(s) + H2O(l)
 4. As a base: 
Ammonia is a weak base; it reacts with acids to form ammonium salts. 
2NH3(g) + H2SO4(aq) ----> (NH4)2SO4(s)
If hydrogen chloride gas is used, dense white fumes composed of suspended particles of ammonium chloride are formed.
NH3(g) + HCl(g) ----> NH4Cl(s)
5. As a precipitating agent: 
Aqueous ammonia precipitates the insoluble hydroxide of metals from solution 
of their salts.
Pb(NO3)2(aq) + 2NH3(g) + 2H2O(l) ----> Pb(OH)2(s) + 2NH4NO3(aq)
CuSO4(aq) + 2NH3(aq) + 2H2O(l) ----> (NH4)2SO4(aq) + Cu(OH)2
 FeCl3(aq) + 3NH3(aq) + 3H2O(l) ----> Fe(OH)3(s) + 3NH4Cl(s)
ZnSO4(aq) + NH3(g) + H2O(l) ----> Zn(OH)2(s) + (NH4)2SO4(aq)
 Some metal hydroxides like copper (ii) and zinc will dissolve in excess ammonia solution to form complex ions.
Cu(OH)2(s) + 4NH3(aq) ----> Cu(NH3)2+4(aq) + 2OH-(aq)
Zn(OH)2(s) + 4NH3(aq) ----> Zn(NH3)2+(aq) + 2OH-(aq)
6. Thermal decomposition: 
Ammonia decomposes at temperatures above 500°C to yield nitrogen and hydrogen. 
2NH3 === N2(g) + 3H2(g)
Tests for Ammonia 
(i) Action of litmus paper: Hold a damp red litmus paper into the jar containing the unknown gas. If the litmus paper turns blue then the gas is 
ammonia.
(ii) Action with hydrochloric acid: Dip a glass rod in concentrated hydrochloric acid and then insert it in the gas jar containing the unknown gas. 
White fumes are formed if the gas is ammonia.
Uses of Ammonia
 1. Ammonia is used in the manufacture of trioxonitrate(v)acid and sodium trioxocar-bonate (iv) by solvay process.
2. It is used in the manufacture of nitrogenous fertilizers.
3. Aqueous ammonia is used in softer temporarily hard water.
4. Liquid ammonia is used in refrigerators as a cooling agent. 
5. Aqueous ammonia is also used in laundries as solvent for removing grease and oil stains.
6. It is used in the production of nylon.



Compiled by
Odusola Ayomikun 

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