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Ammonia is an essential unit of many chemicals and products. Be it its use in fertilizers, plastics, household cleaning agents, or as a refrigerant gas, Ammonia is present in all. Its uses traces to the pharmaceutical industries as well. But what makes Ammonia the most important compound is its ability to synthesize into Ammonium Nitrate and Ammonium Sulfate which are the most important components of artificial fertilizers today and also the secret ingredient for plant growth and its tremendous production around the globe.
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Key Terms: Ammonia, Ammonia carbonate, Pungent odour, Haber’s process, Lewis base, Artificial fertilizer, Ammonium Nitrate, Ammonium Sulfate
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Preparation of Ammonia
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- Ammonia is prepared in compact quantities from the decomposition of a nitrogenous organic matter named Urea. This preparation is also called Laboratory Preparation. The reaction proceeds with the decomposition of Urea with water to form Ammonium Carbonate that further decomposes and undergoes an equilibrium reaction to form Ammonia simultaneously releasing gasses like Hydrogen and Carbon Dioxide. The equation can be represented as the following -:
NH2CONH2 +2H2O ⇔ (NH4)2CO3 2NH3 + H2O + CO2
- Ammonia can also be formed in the laboratory using the easily available ammonium salts such as Ammonium Chloride and Ammonium Sulfate. The reaction can be represented as follows -:
2NH4Cl + Ca (OH) 2 → 2NH3 + 2H2O + CaCl2
- In the above reaction, Ammonium Chloride reacts with Calcium Hydroxide/Slaked Lime and undergoes decomposition to produce small amounts of Ammonia with the simultaneous release of Hydrogen and Calcium Chloride.
(NH4)2 SO4 + 2NaOH → 2NH3 + 2H2O + Na2SO4
- In the above reaction, Ammonium Sulfate reacts with Sodium Hydroxide to give Ammonia along with by-products such as Hydrogen and Sodium Sulfate.
- Ammonia is a versatile chemical compound therefore; laboratory preparation is not enough to meet the massive demands of the industries. To counter the problem, Ammonia is prepared on a large scale using the Haber’s Process, also referred to as the Haber–Bosch process, invented by the German chemists Fritz Haber and Carl Bosch.
- Using Haber’s process, the Ammonia is produced in large quantities and is used worldwide for the production of Nitrogen based fertilizers.
- In this process, Ammonia is synthesized using Nitrogen which is directly taken from the air and Hydrogen usually taken from natural gas in the form of methane and steam in the ratio 1:3 by volume.
- The reaction can be put forward as -:
N2 (g) + 3H2 (g) ⇔ 2NH3 (g) + Heat
- We can see that the reaction produces heat; therefore it is an exothermic reaction. It is very important to note that an exothermic reaction increases the temperature of the reaction because of the heat produced. Therefore, to counter this increase and favour the forwardness, an exothermic reaction always takes place in low temperature.
- However, the lower the temperature, the lower is the rate of reaction. And if the rate of reaction is low then the time taken for the reactants to react and produce the product will be at a very slower pace. Hence, to overcome this problem, the favourable temperature in the Haber’s process was said to be around 450 to 550 degree Celsius. It is said to be favourable because even though it produces low yield, this temperature is optimal to increase the rate of reaction and make the Ammonia at a faster rate.
- Now to overcome the problem of low yield, Haber’s process uses Le Chatelier's Principle. According to the principle, an increase in the pressure will favour the side with less number of molecules. Because fewer molecules are present on the product side than the reactants therefore, it is favourable for the production of Ammonia. It is also interesting to note that pumping high pressure into the reaction will also make the reactants collide more frequently and shift the equilibrium in the forward direction and hence produce large Ammonia yield.
- Therefore, the optimum pressure used in the Haber’s process is 200-250 Atmospheric Pressure.
- The catalyst in any reaction helps in increasing the rate of the reaction without hindering the yield of the reaction. Therefore, in Haber’s process finely powdered Iron is used as a catalyst and to increase the efficiency of the catalyst, a catalyst promoter is used which is none other than Molybdenum.
- The two arrows signify that the reaction is reversible in nature meaning the ammonia formed can be broken back down into Nitrogen and Hydrogen. Therefore, Haber’s Process is a zero waste reaction.
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Properties of Ammonia
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- Ammonia is a colourless gas.
- Ammonia has a strong and unpleasant characteristic pungent odour which can be very irritating and suffocating to the nose.
- Ammonia can be represented as NH3 and the electronic configuration of Nitrogen can be represented as 1s2 2s2 2p3. Therefore, it can be seen that Nitrogen forms 3 bonds with Hydrogen molecules leaving behind a pair of lone pairs. Because of the presence of these lone pairs, Ammonia behaves as a Lewis base.
- Being lighter than air, Ammonia is highly soluble in water.
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Uses of Ammonia
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- Ammonia is used to make artificial fertilizers containing Nitrogen.
- Ammonia can be liquefied under pressure. Therefore, this liquid ammonia is then used as a refrigerant.
- Ammonia is used in the manufacturing of fibers in the textile industry as well as used in making dyes, drugs and cosmetics.
- Ammonia is an essential solvent and is widely used in laboratories.
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Things to Remember
- Ammonia is an essential unit of many chemicals and products.
- Be it its use in fertilizers, plastics, household cleaning agents, or as a refrigerant gas, Ammonia is present in all.
- Its uses traces to the pharmaceutical industries as well.
- Ammonia is prepared in compact quantities from the decomposition of a nitrogenous organic matter named Urea.
- Ammonia is a versatile chemical compound therefore; laboratory preparation is not enough to meet the massive demands of the industries.
- Ammonia is a colourless gas.
- Ammonia has a strong and unpleasant characteristic pungent odour which can be very irritating and suffocating to the nose.
- Ammonia is used to make artificial fertilizers containing Nitrogen.
- Ammonia can be liquefied under pressure. Therefore, this liquid ammonia is then used as a refrigerant.
Read More: Mass Percent Formula
Sample Questions
Ques: Why is the ratio of Nitrogen to Hydrogen taken as 1:3 by volume while preparing Ammonia using Haber’s Process? (2 Marks)
Ans: The ratio of Nitrogen to Hydrogen is taken as 1:3 by volume while preparing Ammonia using Haber’s Process because of Avogadro's Law. According to the law, by using the equal volumes of gases at the same temperature and pressure, we will get equal numbers of molecules. Therefore to make Ammonia which can be written as NH3, we need 1 molecule of Nitrogen and 3 molecules of Hydrogen and thus the ratio is obtained.
Ques: Why is only Iron used as a catalyst in the Haber’s Process? (2 Marks)
Ans: Finely powdered Iron is used as a catalyst in the Haber’s Process because of many reasons. The foremost is its economic value. Iron is cheap as compared to other catalysts and hence widely available. The second is its porous nature. Iron has a porous surface because of which it has the ability to increase the surface area of the reaction and hence also acts as an adsorber. The last but not the least reason is its enhanced stability and its property to withstand high temperature and pressure.
Ques: Why should the Nitrogen and hydrogen used in the Haber’s Process be free from impurities? (2 Marks)
Ans: The Nitrogen and hydrogen used in the Haber’s Process must be free from any kind of impurities because any impurity in the reactants can cause the catalyst to be poisoned. And once the catalyst is poisoned, it won't be able to work as effectively and efficiently as before. Therefore, the catalyst will eventually have to be removed and new catalyst will have to be added for the reaction to begin. To avoid this vigorous problem, impurity free Nitrogen and Hydrogen is used in the Haber’s Process.
Ques: Give an example of how Ammonia acts as a Lewis base. (2 Marks)
Ans: The reaction of Ammonia with water proves that Ammonia acts as a Lewis base. The reaction can be depicted as -: NH3+ H2O → NH4+ + OH-
The OH- ions released prove that Ammonia acts as a Lewis base.
Ques: Give an example of how Ammonia precipitates hydroxides from metal salts. (2 Marks)
Ans: Ammonia has the ability to precipitate hydroxides from any given metal salts.
E.g. – The reaction of Ammonium Hydroxide with Zinc Sulfate. When Ammonium Hydroxide reacts with Zinc Sulfate, Ammonium Sulfate gets precipitated out with the formation of Zinc Hydroxide.
The reaction can be illustrated as the following -: ZnSO4 + NH4OH → Zn (OH) 2 + (NH4)2 SO4
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