Ammonia (NH 3 )

1. Ammonia (NH3) • Ammonia (NH3) is an important compound of nitrogen and hydrogen. It is produced by the natural decomposition of animal and vegetable bodies. Ammonia also occurs in the soil in the form of ammonium salts.

2. Ammonia associate throug hydrogen bonding to form long chains.

3. Structure of ammoniatrigonal pyramidal shape

4. Laboratory Preparation of Ammonia • Ammonia gas is usually prepared in the laboratory by gently heating ammonium chloride (NH4Cl) and slaked lime [Ca(OH)2]. Ammonia gas is lighter than air, necessitating its collection by the downward displacement of air. Because it is highly soluble in water it cannot be collected over it. Passing ammonia gas over quicklime (CaO) dries it.

5. Tests of ammonia • The ammoniacal smell of ammonia is easily detectable having a characteristic pungent smell. • Ammonia turns moist red litmus blue, and moist turmeric paper brown. • When added to a solution of copper sulphate, ammonia turns the solution deep blue. • A glass rod dipped in concentrated HCl when brought close to ammonia, causes dense white fumes. • When added to Nessler's reagent (alkaline solution of K2[HgI4] ammonia gives brown precipitate.

6. Manufacture of Ammonia Haber's process • The manufacture of ammonia by Haber's process involves the direct combination of nitrogen and hydrogen.

7. Conditions • Low temperature • High pressure • Catalyst Finely divided iron containing molybdenum or alumina is used as a catalyst. Molybdenum or alumina (Al2O3) acts as a promoter and increases the efficiency of the catalyst. A mixture of iron oxide and potassium aluminate has been found to work more effectively.

8. Manufacturing plant employed in Haber's process

9. Source of raw materials • The nitrogen and hydrogen gases used as the raw material in Haber's process are obtained as follows. • Nitrogen is obtained from the liquid air and hydrogen from water by electrolysis. • Hydrogen may be obtained from water gas (mixture of CO and H2) by Bosch process. • Water gas can be obtained by passing steam over red hot coke.

10. Plant The plant, which manufactures ammonia, has the following components and processes. • Compressor A mixture of nitrogen and hydrogen is compressed to 200-900 atmosphere pressure, in the ratio 1:3 (by volume). The compressed gas is sent to ammonia converter.

11. Converter

12. Condensers • This cools and liquefies ammonia. The condensed ammonia, called 'liquor ammonia' is filled into cylinders under pressure.

13. Physical Properties of Ammonia • Ammonia is a colorless gas. • It has a pungent odor with and an alkaline or soapy taste. When inhaled suddenly, it brings tears into the eyes. • It is lighter than air and is therefore collected by the downward displacement of air. • It is highly soluble in water

14. It can be easily liquefied at room temperature by applying a pressure of about 8-10 atmosphere. • Liquid ammonia boils at 239.6 K (- 33.5°C) under one atmosphere pressure. It has a high latent heat of vaporization (1370 J per gram) and is therefore used in refrigeration plants of ice making machines. • Liquid ammonia freezes at 195.3 K (-77.8°C) to give a white crystalline solid.

15. Chemical Properties of Ammonia • Thermal stability • Combustibility • Basic character • Reaction With metal oxides • Reaction With halogens • With carbon dioxide (formation of urea) • Reaction With alkali metals • Action with heavy metal ions

16. Uses of ammonia • In the manufacture of fertilizers such as urea diammonium phosphate, ammonium nitrate, ammonium sulphate etc. • In ice plants, as a refrigerant • In furniture industry, as a cleansing agent for furniture and glass surfaces. • In the manufacture of nitric acid by Ostwald's process. • In the manufacture of sodium carbonate by Solvay's process.