How Are Ammonia and Nitric Acid Prepared and Used in Chemistry?
Ammonia is a colourless and foul-smelling gas which is composed of hydrogen and nitrogen. It is a simple and stable compound of both these elements and acts as a starting material to produce several nitrogen compounds. It is also amongst the most commonly present hydrides in the atmosphere. The amount of ammonia in the atmosphere is developed mostly because of the bacterial decomposition that is released from the nitrogen-rich elements from plants and animals.
Azane is the IUPAC name of ammonia. The ammonia chemical formula is NH3. Ammonia is present all around us and we are all exposed to a lower concentration of it in our day to day activities. In this article, we will study the properties and preparation of ammonia and nitric acid, the uses of ammonia, ammonium carbonate uses, and the properties of ammonia.
Preparation Of Ammonia
Smaller quantities of ammonia are present in the air and soil because of the decay of the nitrogenous organic matter. To produce ammonia on a small scale, ammonium salts and caustic soda are made to react with each other.
2NH4Cl + Ca(OH)2 → 2NH3 + 2H2O + CaCl2
For a large scale production, Haber’s process is used. The steps that are involved in Haber’s process are:
N2(g) + 3H2(g) ↔ 2NH3 (g)
Nitrogen and hydrogen are used in the form of raw materials for this reaction. The impurities for the gases get removed by a process known as scrubbing.
After this process of scrubbing, the gases are combined and then passed through a compressor. Then the mixture is compressed under a 200 atm pressure.
Then the compressed gases are passed to a converter in which the gases are heated up at a temperature of 450°C and 200 atm pressure. The nitrogen then tends to react with the hydrogen and forms ammonia, however, just about 15% of the total gas is formed.
The mixture of ammonia, nitrogen, and hydrogen is then removed from the converter and cooled wherein it tends to liquefy in the tank and then collected.
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Physical Properties of Ammonia
Chemical Properties of Ammonia
Ammonia is highly soluble in water. The NH3 aqueous solution is a weak base since OH- ions get formed.
NH3 + H2O → N4+ + OH-
Ammonium salts get formed when ammonia reacts with an acid.
ZnSO4 + 2NH4OH (g) → Zn(OH)2 + (NH4)2SO4
Uses of Ammonia
The liquid ammonia includes being used as a refrigerant.
The ammonia gas uses include the manufacturing of urea which is excellent nitrogen fertilizer.
The ammonia solution uses include removing grease since it has cleansing properties.
Nitric Acid
Friedrich Wilhelm Ostwald in the starting of the 20th century had developed a process wherein ammonia was used for obtaining nitric acid. Due to the development of nitric acid, it had helped the Germans in World War I for making explosives and not importing it from other countries such as Chile. The chemical formula of nitric acid is denoted by HNO3.
Preparation of Nitric Acid
For the small scale preparation, nitric acid is made when concentrated sulphuric acid is heated along with NaNO3 or KNO3.
NaNO3 + H2SO4 → NaHSO4 + HNO3
For the large scale preparations of nitric acid, the Ostwald process is used.
In this process, ammonia undergoes catalytic oxidation through oxygen present in the atmosphere. This happens in the presence of Pt/Rh in the form of a catalyst at 500 K temperature and a pressure of 9 bars.
4NH3 + 5O2 → 4NO(g) + 6H2O
The nitric oxide obtained is then reacted with the oxygen to form NO2.
2NO + O2 → 2NO2(g)
The NO2 formed is then made to dissolve in H2O which forms HNO3.
3NO2 (g) + H2O(l) → 2HNO3(aq) + NO(g)
Properties of HNO3
Nitric acid is colourless in nature.
The boiling point of liquid nitric acid is 84.1°C and it tends to freeze at -41.55 °C and forms a white solid.
It is a strong acid that dissociates and forms nitrate ion and hydronium.
HNO3(aq) +H2O (l) → H3O+(aq) + NO3-(aq)
Nitric acid in its concentrated state tends to act as a strong oxidising state
Cu + 4HNO3 → Cu(NO3)2 + 2NO2 + 2H2O
FAQs on Ammonia and Nitric Acid: Key Formulae, Properties & Preparation
1. What are the key physical and chemical properties of ammonia (NH₃)?
Ammonia is a colourless gas with a distinct pungent smell. Its key properties are:
- Physical Properties: It is highly soluble in water due to hydrogen bonding. In a solid and liquid state, it is associated with hydrogen bonds, resulting in higher melting and boiling points than expected based on its molecular mass.
- Chemical Properties: Ammonia is a Lewis base due to the lone pair of electrons on the nitrogen atom. It reacts with acids to form ammonium salts (e.g., NH₃ + HCl → NH₄Cl). It can also act as a ligand to form coordination compounds with metal ions.
2. How is ammonia manufactured on an industrial scale by the Haber-Bosch process?
Ammonia is manufactured industrially by the Haber-Bosch process, which involves the direct combination of dinitrogen (N₂) and dihydrogen (H₂) gases. The reaction is reversible and exothermic: N₂(g) + 3H₂(g) ⇌ 2NH₃(g). To maximise the yield, specific conditions are maintained based on Le Chatelier's principle:
- Pressure: A high pressure of about 200 atm is applied to favour the forward reaction.
- Temperature: An optimum temperature of around 400 – 450 °C is used as a compromise between a favourable equilibrium position and a fast reaction rate.
- Catalyst: An iron oxide catalyst with small amounts of K₂O and Al₂O₃ is used to speed up the attainment of equilibrium.
3. What are the essential steps in manufacturing nitric acid (HNO₃) via the Ostwald process?
The Ostwald process manufactures nitric acid from ammonia in three main steps:
- Catalytic Oxidation of Ammonia: Ammonia gas is mixed with air and passed over a platinum-rhodium gauze catalyst at about 500 K and 9 bar pressure. Ammonia is oxidised to nitric oxide (NO).
4NH₃(g) + 5O₂(g) → 4NO(g) + 6H₂O(g) - Oxidation of Nitric Oxide: The nitric oxide formed is then reacted with more oxygen to form nitrogen dioxide (NO₂).
2NO(g) + O₂(g) → 2NO₂(g) - Absorption in Water: The nitrogen dioxide is dissolved in water in an absorption tower, where it forms nitric acid. Oxygen is bubbled through to facilitate the reaction.
3NO₂(g) + H₂O(l) → 2HNO₃(aq) + NO(g)
4. What happens when ammonia reacts with nitric acid?
When ammonia (a base) reacts with nitric acid (an acid), they undergo a neutralisation reaction to form the salt ammonium nitrate (NH₄NO₃). The balanced chemical equation is:
NH₃(aq) + HNO₃(aq) → NH₄NO₃(aq)
This reaction is highly exothermic. Ammonium nitrate is a major industrial chemical used as a high-nitrogen fertiliser and is also a component of certain explosives.
5. How does the structure of ammonia explain its properties as a Lewis base?
Ammonia (NH₃) has a trigonal pyramidal structure. The central nitrogen atom is sp³ hybridised, forming three single bonds with hydrogen atoms and having one lone pair of electrons. The presence of this available lone pair allows ammonia to donate it to an electron-deficient species (a Lewis acid), such as a proton (H⁺) or a metal cation. This ability to donate an electron pair is the definition of a Lewis base, which explains its characteristic basic nature and its ability to form coordinate bonds in complexes like [Cu(NH₃)₄]²⁺.
6. Why does concentrated nitric acid act as a powerful oxidising agent?
Concentrated nitric acid (HNO₃) is a strong oxidising agent because the nitrogen atom is in its highest possible oxidation state (+5). This makes it highly unstable and eager to accept electrons to be reduced to a lower, more stable oxidation state (e.g., +4 in NO₂, +2 in NO). The decomposition of nitric acid produces nascent oxygen, which is a powerful oxidising agent.
For example, it can oxidise non-metals like carbon to carbon dioxide:
C + 4HNO₃ (conc.) → CO₂ + 2H₂O + 4NO₂
7. What is the phenomenon of passivity caused by nitric acid on certain metals?
When some metals like iron (Fe) or aluminium (Al) are treated with concentrated nitric acid, they become 'passive' or chemically unreactive. This is not because the metal is inert, but because the strong oxidising nature of the acid forms a very thin, non-porous, and stable layer of metal oxide on the metal's surface. For iron, this is a layer of iron(III) oxide (Fe₂O₃). This protective oxide layer prevents the acid from further attacking the metal underneath, rendering it passive. This principle is important for protecting metals from corrosion.
8. What is the key difference between the laboratory preparation and industrial preparation of nitric acid?
The main difference lies in the reactants and scale of production.
- Laboratory Preparation: Nitric acid is prepared on a small scale by heating a nitrate salt like potassium nitrate (KNO₃) or sodium nitrate (NaNO₃) with concentrated sulphuric acid (H₂SO₄). The more volatile nitric acid distils over.
NaNO₃ + H₂SO₄ → NaHSO₄ + HNO₃ - Industrial Preparation (Ostwald Process): This is a large-scale, continuous process that uses ammonia (NH₃) and air as the primary raw materials. It is a more economical and efficient method for producing the large quantities required for fertilisers and other industries.
