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Dinitrogen (N2), which is also regarded as the VIPs of the nitrogen family, is one of the important compounds of this family. Dinitrogen is an exceedingly unreactive molecule and chemists have long dreamed about how it can be converted into useful compounds. Commercially, dinitrogen is prepared by the liquifaction and fractional distillation of air as it is an abundant element found in the air. This element was first discovered by Scottish physician Daniel Rutherford in 1772.
Also Read: Nitric Acid
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Key Terms: Dinitrogen, p-block elements, isotopes of nitrogen, molecule, air, compounds, diatomic gas, environment
Dinitrogen
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Dinitrogen is an important element in our environment. It is a diatomic gas.
| Sl. No. | Properties | |
|---|---|---|
| 1. | Total percentage of Dinitrogen in atmosphere | 78% |
| 2. | First Discovered year | 1772 |
| 3. | Discovered by | a Scottish physician Daniel Rutherford |
| 4. | Symbol of the chemical element | N |
| 5. | Atomic Number | 7 |
This portion is a part of p-block elements and carries a total weightage of 6 to 7 marks and 7 periods.
Read more: Aqua Regia
Properties of Dinitrogen
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Physical Properties
- Colorless
- Odorless
- Diamagnetic nature
- Non-toxic gas
Solubility Nature
- It is sparingly soluble in water.
Characteristic upon condensation
- Nitrogen undergoes condensation to form a colourless liquid which on solidification results in the formation of snow like mass.
Chemical Properties
- Dinitrogen has a high bond enthalpy due to the N = N bond
- It is inert at room temperature.
- The reactivity increases as the temperature increases.
Characteristics upon reaction with Metal
- At high temperatures, nitrogen molecules react with metals to form respective ionic nitrides and with non-metals to form covalent nitrides.
6Li +N2heat 2Li3N
Characteristic upon reaction with hydrogen
- Name of the process: Haber’s Process.
- Reaction : N2(g) + 3H2(g) 773k 2NH3(g); Production of Ammonia at 773K
Characteristic upon reaction with Oxygen
- Final Product : Nitric Oxide
- Reaction : N2(g) + O2(g) ↔ heat 2NO(g)
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Preparation of Dinitrogen
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Nitrogen is obtained commercially by liquefaction and fractional distillation of air. This process mainly involves two steps:
Step 1
- Air is reduced to liquid air by applying high pressure ranging between 100 and 200 atmospheres.
- This compressed air is then passed through fine jet where it undergoes expansion.
- This method is repeated several times which results in the formation of liquid air.
Step 2
- The liquid formed undergoes fractional distillation.
- The boiling point of dinitrogen is lower than that of the liquid oxygen and hence it distils out, leaving behind liquid oxygen.
- Nitrogen is obtained from the impure liquid.
A) In laboratory, dinitrogen is obtained by reacting aqueous solution of ammonium chloride with sodium nitrite.
Reaction: NH4Cl(aq) + NaNO2(aq) → N2(g) + 2H2O(l) + NaCl(aq)
The products obtained consists of impurities such as NO and HNO3 which can be removed by thermal decomposition of ammonium dichromate.
B) Another method to remove the impurities is to pass the gaseous mixture through sulphuric acid containing potassium dichromate.
Reaction: (NH4)2Cr2O7 → N2 + 4H2O + Cr2O3
C) Decomposition of sodium or Barium azide in the presence of high temperature also results in the formation of pure nitrogen.
Read more: Nitrogen
Uses of Dinitrogen
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- Production of Ammonia.
- Production of Calcium cyanamide
- Used in Iron manufacture industry
- Used in Steel manufacture industry
- Liquid nitrogen is used in food industry
Nitrogen has two stable isotopes
14N and 15N
Solubility
It has a very low solubility in water (23.2 cm3 per litre of water at 273 K and 1 bar pressure) and low freezing and boiling points.
Read more: P-Block Elements MCQ
Different forms of oxide of nitrogen
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Table 2:
| Sl. No. | Name | Formula | Oxidation state | Physical appearances and chemical nature |
|---|---|---|---|---|
| 1. | Dinitrogen Oxide Nitrogen(I) Oxide | N2O | +1 | Colorless gas Neutral |
| 2. | Nitrogen Monoxide Nitrogen(II) Oxide | NO | +2 | Colorless gas Neutral |
| 3. | Dinitrogen trioxide Nitrogen(III) Oxide | N2O3 | +3 | Blue solid Acidic |
| 4. | Nitrogen Dioxide Nitrogen(IV) Oxide | NO2 | +4 | Brown gas acidic |
| 5. | Dinitrogen tetraoxide Nitrogen(IV) Oxide | N2O4 | +4 | Colourless solid liquid, acidic |
| 6. | Dinitrogen Pentaoxide Nitrogen(V) Oxide | N2O5 | +5 | Colorless solid Acidic |
Read Also: Electron Gain Enthalpy
Sample Questions
Ques. Write the reaction of thermal decomposition of sodium azide. (2 marks)
Ans. Thermal decomposition of Sodium Azide gives Dinitrogen gas. 2NaN3 → 2Na + 3N2
Ques. Nitrogen exhibits +5 oxidation state, but why it does not form pentahalide? (2 marks)
Ans. Nitrogen with n = 2, has s and p orbitals only. It does not have d orbitals to expand its covalence beyond four. That is why it does not form pentahalide.
Ques. Why does NH3 act as a Lewis base? (2 marks)
Ans. Nitrogen atom in NH3 has one lone pair of electrons which is available for donation. Therefore, it acts as a Lewis base.
Ques. Why does NO2 dimerise? (2 marks)
Ans. NO2 contains odd number of valence electrons. It behaves as a typical odd molecule. On dimerization, it is converted to stable N2O4 molecule with even number of electrons.
Ques. What are the major utilizations of Nitric Acids? (2 marks)
Ans. The major use of nitric acid is in the manufacture of ammonium nitrate for fertilisers and other nitrates for use in explosives and pyrotechnics. It is also used for the preparation of nitro-glycerine, trinitrotoluene and other organic nitro compounds. Other major uses are in the pickling of stainless steel, etching of metals and as an oxidiser in rocket fuels.
Ques. In laboratory, what are the major process for production of Nitric Acid? (2 marks)
Ans. In the laboratory, nitric acid is prepared by heating KNO3 or NaNO3 and concentrated H2SO4 in a glass retort.
NaNO3 + H2SO4 = NaHSO4 + HNO3
Ques. What are the major acids which are formed by Nitrogen? (2 marks)
Ans. Nitrogen forms oxoacids such as H2N2O2 (hyponitrous acid), HNO2 (nitrous acid) and HNO3 (nitric acid). Amongst them HNO3 is the most important.
Ques. Briefly describe the Haber’s process. (2 marks)
Ans. On a large scale, ammonia is manufactured by Haber’s process.
N2 (g) + 3H2 (g) ↔ Ö 2NH3 (g); Δ f H 0 = – 46.1 kJ mol–1
In accordance with Le Chatelier’s principle, high pressure would favour the formation of ammonia. The optimum conditions for the production of ammonia are a pressure of 200 x 105 Pa (about 200 atm), a temperature of ~ 700 K and the use of a catalyst such as iron oxide with small amounts of K2O and Al2O3 to increase the rate of attainment of equilibrium.
Ques. What is the Brown Ring Test in laboratory? When it is used? (2 marks)
Ans. Brown Ring Test: The familiar brown ring test for nitrates depends on the ability of Fe2+ to reduce nitrates to nitric oxide, which reacts with Fe2+ to form a brown coloured complex. The test is usually carried out by adding dilute ferrous sulphate solution to an aqueous solution containing nitrate ion, and then carefully adding concentrated sulphuric acid along the sides of the test tube. A brown ring at the interface between the solution and sulphuric acid layers indicates the presence of nitrate ion in solution.
Ques 1. Give reasons for the following: N2 is less reactive at room temperature. (AI 2015) (2 marks)
Ans. The n atoms in the N2 molecule are held together by the triple bonds. The bond dissociation energy in it is very high (941.4 kJ mol-1). Hence N2 is inactive at room temperature.
Ques 2. Write the reaction of thermal decomposition of sodium azide. (Delhi 2007) (2 marks)
Ans. Nitrogen gas is given out by thermal decomposition of the sodium azide.
2NaN3 → 2Na + 3N2
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