The Basics of Ammonia and Nitric Acid
Students may already have been introduced to the compound ammonia, and have some idea about its composition. It is a combination of three hydrogen atoms or molecules and nitrogen. The combination leads to the formation of ammonia gas. Besides this, an understanding of the properties of ammonia is also important.
We will not go into a relatively elaborate discussion on ammonia but also focus on its important attributes. By the end of this discussion, you will also have an idea about the laboratory preparation of ammonia acid. Do note, this is a vital chapter in your curriculum.
Nature of Ammonia
Now, we will discuss the nature and other properties of ammonia in the upcoming paragraph. Ammonia is also called nitrogen trihydride or azane. NH3 is the chemical formula for ammonia. The NH3 molecule has a trigonal pyramidal shape. The hybridisation of this molecule is sp3. Nitrogen is the base of ammonia which here makes a single electron pair. It can also form a homogeneous mixture with water. It is a polar molecule. If we compare it with NF3, in spite of the fact that fluorine is the most electronegative element, the resultant dipole of NH3 is greater than NH3. The reason is, that in NH3 the orbital dipole of hydrogen is in the same direction as nitrogen.
On the other hand, the orbital dipole of fluorine is in the opposite direction with nitrogen. It also plays a very important role in the human body system. The kidneys secrete ammonia, which helps in the neutralization of acids within the body. It also occurs naturally in our environment, some in volcanic areas and some in rainwater.
Structure of Ammonia
The molecules of ammonia exhibit a pyramidal shape and the nitrogen atom is placed at the vertex. Ammonia molecules constantly undergo inversion motion wherein the nitrogen atom moves through the plane of a hydrogen atom-like an upside-down umbrella.
The properties of ammonia that are seen are owing to ammonia acting as a base. The atom of nitrogen may either bond to a metal cation or to a proton such as forming an ammonium ion.
When the ammonia is frozen or in liquid form, there exists molecular attraction through the shared hydrogen atom between two molecules. Such sharing is called hydrogen bonding. Due to this bond, an association takes place leading to the formation of compounds that contain free electrons that may be obtained by treating ammonia solutions with various complexing agents.
Properties of Ammonia
The physical properties of ammonia are listed below in detail–
Colorless gas having a pungent and suffocating odor.
Freezing point is -77.7°C.
Boiling point is -33.35°C.
Lighter than air given its density to be 0.583 times of air.
Molar mass is 17.03g/mol.
Given the extremely low boiling point of ammonia, liquid ammonia can be readily stored at high pressure and low temperature. In its purest form, anhydrous ammonia can readily absorb moisture (hygroscopic). It also retains alkaline properties and amounts to being corrosive.
Do You Know?
Research studies have found out that ammonia can have a toxic effect on the glial and nerve cells of the brain. While in healthy people, ammonia is converted into urea in the liver which is eventually washed out with urine, there could be excessive concentration of ammonia in blood for people with impaired liver function. The higher levels lead to ammonia toxicity triggering seizures and coma.
Laboratory Preparation of Ammonia
Ammonia is prepared by the Haber-Bosch process. The process, in principle, combines nitrogen from the air with that of hydrogen that is mainly derived from natural gas such as methane. It leads to the production of ammonia. The production of ammonia is exothermic, and this reaction is reversible in nature.
In the presence of a metal catalyst, elemental hydrogen and elemental nitrogen are reacted which gives out ammonia gas. The reaction is conducted at very high pressure as well as high temperature (400-550°C).
Uses of Ammonia
Ammonia acts as a precursor to different nitrogen compounds like amino acids, urea, phenol, hydrogen cyanide, acrylonitrile, nitric acid, soda ash, among others.
It finds extensive usage in the production of polymers, fertilizers, synthetic fibers such as rayon and nylon, cleaning agents, refrigerants along with explosives like nitroglycerin and TNT.
Even though ammonia is present and finds usage in many household products and purposes; its inhalation can be highly toxic. The fumes of ammonia have a very sharp and pungent odor that can cause irritation in nose, eye, mucous membranes and skin. It can also cause severe damage to the respiratory tract. When exposed to a very high concentration of ammonia gas, it may lead to permanent lung damage or even death.
What is Nitric Acid?
Nitric acid is a strong acid with a pH level of 1.2 and is also called aqua fortis and the spirit of nitre. The chemical formula for nitric acid is HNO3. Nitric acid is formed by the reaction Of water and nitrogen dioxide. The reaction is as follows-
3NO2 + H2O → HNO3 + NO. It reacts with metals, hydroxides and oxides to form salts.
Properties of Nitric Acid
Nitric acid is a fuming, colorless and highly corrosive agent.
Freezing point is -42°C.
Boiling point is 83°C.
PH is approximately 3.01.
Nitrogen atom is bonded to a hydroxyl group and forms equivalent bonds with the rest oxygen atoms.
It is a conjugate acid of a nitrate.
Test Yourself
The Factories Producing Fertilizers Need to have Plant(s) of-
ammonium nitrate production.
nitric acid production.
ammonia production.
all of the above.
2. During Ammonia Production, Low Temperature is Maintained. The Benefit of Low Temperature –
better yields only.
better quality.
slow and better yields.
better quality.
3. _______________ can be Used to Catalyze the Synthesis of Ammonia.
Iron
Nickel
Platinum
Aluminum
Solutions: 1. (d) all of the above
2. (c) slow and better yields
3. (a) Iron
Laboratory Preparation of Nitric Acid
Laboratory preparation of Nitric Acid (HNO3) involves heating of nitrate salt with that of concentrated sulphuric acid.
Nitric acid vapor is condensed into brown-coloured liquid within a receiver that is cooled by cold water. The oxides of nitrogen that remain dissolved in the mixture are removed by way of re-distillation.
Uses of Nitric Acid
Nitric acid has several industrial uses and acts as a building block chemical for many other chemical compounds. It is used for the manufacture of different polymers such as polyurethane and polyamide.
It is used to make explosives such as nitro-glycerine and trinitrotoluene (T.N.T). Nitric acid also finds usage in the aerospace industry as rocket propellant.
Nitric acid is used in fertilizer production such as ammonium nitrate, calcium nitrate etc. It is also used in our daily lives as laboratory reagents, for cleaning food and dairy equipment, among others.
Chemistry can prove to be one of the difficult subjects that you may have to prepare in your syllabus. However, you can join our online classes where even the basics of the subject will be explained along with providing clarification of all your doubts on ammonia and nitric acid formulae properties preparation.
Various topics, such as properties of ammonia, are frequently touched upon in examination. Hence, when you have a clear understanding of such topics, you can hit the ground running in terms of preparation.
FAQs on Ammonia and Nitric Acid
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 as per the CBSE syllabus are:
- Physical Properties: It is lighter than air and is highly soluble in water. It can be easily liquefied due to strong hydrogen bonding between molecules, with a boiling point of -33.35°C and a freezing point of -77.7°C.
- Chemical Properties: It is a weak base in aqueous solution, forming ammonium hydroxide (NH₄OH). Due to the lone pair of electrons on the nitrogen atom, it acts as a Lewis base, donating the electron pair to form coordination compounds.
2. How is ammonia commercially prepared? Explain the Haber-Bosch process.
Ammonia is manufactured on a large scale using the Haber-Bosch process. This process involves the direct combination of dinitrogen (N₂) from the air with dihydrogen (H₂) obtained from natural gas. The reversible reaction is: N₂(g) + 3H₂(g) ⇌ 2NH₃(g). To maximise the yield, the reaction is carried out under optimal conditions: a high pressure of around 200 atmospheres, a temperature of approximately 700 K, and in the presence of a catalyst like iron oxide with small amounts of K₂O and Al₂O₃ as promoters.
3. What are the main industrial and household uses of ammonia?
Ammonia has several important applications:
- Fertiliser Production: A vast majority of ammonia is used to produce nitrogenous fertilisers like ammonium nitrate, urea, and ammonium sulfate.
- Industrial Chemicals: It is a crucial starting material for the manufacturing of other inorganic nitrogen compounds, most notably nitric acid via the Ostwald process.
- Refrigerant: Due to its high heat of vaporisation, liquid ammonia is widely used as a refrigerant in large-scale refrigeration plants, known as Refrigerant R717.
- Cleaning Agent: Aqueous solutions of ammonia are effective household cleaners for removing grease and cleaning windows.
4. How is nitric acid prepared on a large scale using the Ostwald process?
The large-scale production of nitric acid is done via the Ostwald process, which occurs 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 to form nitric oxide (NO).
- Oxidation of Nitric Oxide: The nitric oxide formed is then reacted with more oxygen to form nitrogen dioxide (NO₂).
- Absorption in Water: The nitrogen dioxide is absorbed in water to form nitric acid (HNO₃). The NO gas formed during this step is recycled.
This method is highly efficient and is the primary industrial route for nitric acid synthesis.
5. What happens when ammonia reacts with nitric acid? Explain the type of reaction.
When ammonia (a weak base) reacts with nitric acid (a strong acid), they undergo an acid-base neutralisation reaction. This reaction is highly exothermic and results in the formation of a salt, ammonium nitrate. The balanced chemical equation is:
NH₃ (aq) + HNO₃ (aq) → NH₄NO₃ (aq)
Ammonium nitrate is an important compound used extensively as a high-nitrogen fertiliser and also in the manufacturing of explosives.
6. Why does ammonia (NH₃) act as a Lewis base?
Ammonia acts as a Lewis base because the central nitrogen atom in the NH₃ molecule has a lone pair of electrons that is not involved in bonding. According to the Lewis definition, a base is a substance that can donate an electron pair. Ammonia can readily donate this lone pair to an electron-deficient species (a Lewis acid), such as a proton (H⁺) or a metal cation, to form a coordinate covalent bond.
7. How do the structure and bonding in ammonia (NH₃) differ from that in nitric acid (HNO₃)?
The structure and bonding in ammonia and nitric acid are fundamentally different:
- Ammonia (NH₃): The central nitrogen atom is sp³ hybridised, leading to a trigonal pyramidal geometry. It has three bond pairs (N-H) and one lone pair, resulting in an H-N-H bond angle of approximately 107.8°.
- Nitric Acid (HNO₃): The central nitrogen atom is sp² hybridised, resulting in a planar structure. It forms one bond with a hydroxyl group (OH) and two bonds with oxygen atoms, one of which is a double bond. The structure exhibits resonance, delocalising the charge across the O-N-O system.
8. Why is concentrated nitric acid a strong oxidising agent?
Concentrated nitric acid (HNO₃) is a strong oxidising agent because the nitrogen atom is in its highest possible oxidation state of +5. In this state, nitrogen has a strong tendency to accept electrons and be reduced to lower oxidation states (like +4 in NO₂, +2 in NO, or even -3 in NH₃). This strong tendency to gain electrons is what makes it a powerful agent for oxidising other substances, including non-metals and less reactive metals.
9. Despite fluorine being more electronegative, why is the dipole moment of ammonia (NH₃) greater than that of nitrogen trifluoride (NF₃)?
This is a classic example of how molecular geometry affects polarity. In both molecules, the central nitrogen has a lone pair of electrons contributing to the overall dipole.
- In Ammonia (NH₃), the individual N-H bond dipoles point towards the more electronegative nitrogen atom. The dipole moment of the lone pair also points in the same general direction. All these vectors add up, resulting in a large net dipole moment (1.47 D).
- In Nitrogen Trifluoride (NF₃), the highly electronegative fluorine atoms pull electron density away from the nitrogen. The N-F bond dipoles point away from the lone pair's dipole. This causes the bond dipoles to partially cancel out the lone pair's dipole, resulting in a very small net dipole moment (0.23 D).
