Thursday, March 23, 2023

Nitrogen

Nitrogen

Introduction

·      Discovered by Danial Rutherford in 1772.

·      Lavoisier later proved that it does not support respiration and combustion.

·      Present at about 75% by mass and 78% by volume in the atmosphere.

·      All living beings contain nitrogen in the form of proteins.

·      Their abundance in natural inorganic minerals is relatively low probably due to the inertness of N2.

Atomic number: 7                       Atomic mass: 14 amu

E.C.: 1s22s22p3                             Molecular mass: 28 Dalton

Position in the periodic table

Nitrogen is placed along with Phosphorous, Arsenic, Antimony and Bismuth in group VA (15) of the periodic table. This group is called the nitrogen family.

1.       These elements have 7 electrons, so have ns2np3 outermost shell electronic configurations.

Nitrogen -             N (7)                [He] 2s2 2p3

Phosphorous -      P (15)             [Ne] 3s2 3p3

Arsenic-                As (33)            [Ar] 3d10 4s2 4p3

Antimony-            Sb (51)             [Kr] 4d10 5s2 5p3

Bismuth-               Bi (83)              [Xe] 4f14 5d10 6s2 6p3

Uses of Nitrogen

·         In the manufacture of Ammonia.

·         In metallurgy to provide an inert atmosphere.

·         As inert gas in gas-filled electric bulbs.

·         Liquid nitrogen is used as a refrigerant and in cryosurgery.

1.       Nitrogen gas was discovered by

a.       Daniel Rutherford                c. Earnest Rutherford

b.       Lavoisier                                d. Humphrey Davy

2.       Which of the following is not correct for nitrogen?

a.       Its electronegativity is high.

b.       d-orbitals are available for bonding.

c.        It is a typical nonmetal.

d.       Its molecular size is small.

 

9.4.1 Reason for inertness of nitrogen and active nitrogen

The nitrogen molecule, N2, contains a triple bond N=N with a short bond length of 1.09 Å. This bond is very stable (Strong) and the dissociation energy is very high (945.4 KJ mol-1). Because of this high bond energy, the activation energy of the reaction of molecular nitrogen is very high. Thus N2 is inert at room temperature.

When an electrical discharge is passed through nitrogen in a low-pressure yellow glow is formed which persists for a short time even after the gas moves from the region of discharge. This is called active nitrogen. This is more reactive than ordinary nitrogen. Other major sources of active nitrogen are lightening, the reaction of nitrous oxide with excited oxygen atoms in the stratosphere etc.

3.       The total number of electrons that take part in forming the bond in N2 is

a.       2                      b. 4                         c. 6                          d. 10

4.       Nitrogen is inert because

a.       It has a small size.                        C. It is highly electronegative.

b.       It has a stable configuration.     D. It has high dissociation energy.

5.       The cause of the inertness of nitrogen is

a.       high bond energy                        c. absence of bond polarity

b.       short intermolecular distance   d. multiple bonds

9.4.2 Chemical properties of Ammonia

1.      Basic Nature

Write the Lewis structure of ammonia.

·         It behaves as a Lewis base due to the presence of a lone pair of electrons in the central Nitrogen atom.

·         Ammonia dissolves in water giving OH- ions.

NH3 + H2O                  NH4OH                      NH4+ + OH-

Thus the aqueous solution of ammonia (aq. NH3), ammonium hydroxide and ammonia solution mean the same thing.

·         Ammonia changes the colour of moist litmus blue.

·         Ammonia reacts with acids forming salts.

NH3 + conc. HCl                   NH4Cl

                                                 (White dense fumes)

NH3 + HNO3               NH4NO3

2 NH3 + H2SO4             (NH4)2SO4

1.       Why is ammonia highly soluble in water?                                       1

(Hint: Due to the formation of hydrogen bonds and due to the formation of NH4OH with water which is highly soluble in water)

2.       Why ammonia is not dried over conc. H2SO4 acid?                          2

Solution: Ammonia is not dried over conc. H2SO4, as it reacts to give salt, ammonium sulphate.                   NH3 + H2SO4                       (NH4)2SO4

2.       Reduction reactions

a)      Combustion: Ammonia burns in an atmosphere of oxygen with a greenish-yellow flame producing N2 and H2O.

4 NH3 + 3 O2                    2 N2 + 6 H2O

b)      Formation of nitric oxide: When a mixture of ammonia and oxygen gas is passed over heated platinum gauze (800oC), it is oxidized to nitric oxide.

4 NH3 (g) + 5 O2(g)                4 NO (g) + 6 H2O

3.       How does ammonia react with Oxygen?                                      1

4.       What happens when a mixture of ammonia and oxygen is passed over platinum gauze heated to 800oC? 1

3.       Complex formations

Salt of d-block elements like copper, silver, nickel, cobalt, cadmium etc. form soluble complexes with ammonium hydroxide.

e.g white precipitate of AgCl dissolves in ammonia solution giving a soluble complex.

CuSO4 solution gives bluish-white ppt. on treatment with ammonia. On adding excess ammonia, it dissolves giving a deep-blue solution of tetraamine copper sulphate (a complex compound).

5.       What happens when the precipitate obtained by the addition of AgNO3 solution on sodium chloride is treated with ammonia solution?                                                                        2

6.       Write the action of ammonia on the CuSO4 solution.                       1

7.       How does ammonia react with the CuSO4 solution?                        1

8.       What happens when a gas obtained by heating slaked lime and ammonium chloride is passed through a copper sulphate solution?                                                                          1

4. Precipitation reactions

Salt of heavy metals like Iron, Chromium, Aluminium, Zinc etc are precipitated as their hydroxides from their solutions.

These reactions can be used for the confirmatory test for the presence of respective metal ions in the solution.

9.       What is the action when ammonia is passed through the FeSO4 solution?      

10.   How does ammonia react with FeCl3 solution?                                1

5. Reaction with Mercurous nitrate paper

Ammonia forms a black precipitate with mercurous salts.

11.   Write the action of ammonia on mercurous nitrate paper.          1

12.   What is the action when ammonia is passed through mercurous nitrate paper?

13.   What happens when mercurous nitrate paper is placed over a jar containing ammonia gas?     1

14.   What happens when mercurous nitrate paper is exposed to ammonia gas?      1

15.   How does ammonia react with mercurous paper?                            1

6.       The shape of NH3 is

a.       Pyramidal      b. planar                c. tetrahedral        d. linear

7.       Which one is not a property of ammonia

a.       It is lighter than air.                                     C. It is soluble in water.

b.       It is a supporter of combustion.                D. It is a basic gas.

8.       Liquid ammonia is used as a refrigerant because

a.       It is liquid.                      C. It is highly basic.

b.       It is polar.                      D. It has high enthalpy of vaporization.

9.       Oxidation of ammonia yields

a.       NO2                         b. N2O                    c. NO                      d. N2O5

10.    Ammonia solution fairly dissolves

a.       PbCl2                                              b. Hg2Cl2                         c. Cu(OH)2                    d. Al(OH)3

11.    When ammonia is passed through copper sulphate solution, the blue-coloured solution obtained is, due to the formation of

a.       [Cu(NH3)4]SO4                                              c. [Cu(NH3)2]SO4

b.       Cu(OH)2                                                              d. [Cu(SO4)2]NH4

12.    2Na + 2NH3                                           2NaNH2 + H2

In the above reaction,

a.       Na is oxidized                                               d. Na is reduced

b.       Na remains unchanged             

c.        Na undergoes both oxidation and reduction

13.    A gas formed by passing ammonia over heated sodium metal is

a.       N2                    b. H2                       c. NO                      d. N2O

14.    When NH3 gas is passed into mercurous nitrate solution

a.       A black colour of Hg(NH2)NO3 and Hg is formed.

b.       A black colour of Hg(NH3)NO3 is formed.

c.        A reddish brown HgO.NH2 is formed.

d.       A black colour of Hg(NH3)NO3 is formed.

15.    Ammonia reacts with Nessler's reagent to give

a.       A violet precipitate                      c. a deep blue precipitate

b.       A white precipitate                      d. a brown precipitate

16.    To which of the following gaseous mixture is Dalton’s low not applicable?

a.       Ne + He + SO2                                              c. O2 + N2 + CO2

b.       NH3 + HCl + HBr                            d. N2 + H2 + O2

9.4.3 Applications of Ammonia

·         As a laboratory reagent in the name of ammonium hydroxide.

·         To produce urea, ammoniumsulphate & other nitrogen fertilizers.

·         To produce nitric acid, sodium carbonate etc.

9.4.4 Harmful effects of ammonia

·         Ammonia is irritating and corrosive. Exposure to high concentrations of ammonia in the air causes immediate burning of the nose throat and respiratory tract. This can cause respiratory distress or even failure. Inhalation in lower concentration can cause coughing and nose-throat irritation.

·         Exposure to ammonia in low concentration may produce rapid skin or eye irritation. Higher concentration may cause serious injury or burn, permanent eye damage or blindness.

·         Exposure to high concentrations of ammonia by swallowing ammonia solution results in corrosive damage to the mouth, throat and stomach.

9.4.5 Oxyacids of nitrogen (Name and formula)

There are two oxyacids of nitrogen viz nitrous acid (HNO2) and nitric acid (HNO3).

The oxidation numbers of nitrogen in these two acids are +3 and +5 respectively. N2O3 and N2O5 are the anhydrides of nitrous acid and nitric acid respectively.

Nitrous acid is relatively unstable and cannot be stored. It is prepared by mixing solutions of NaNO2 and HCl as

NaNO2 + HCl                     HNO2 + NaCl

It easily disproportionate into HNO3 and NO as

       3 HNO2                       HNO3 + NO + H2O

9.4.6 Chemical properties of Nitric Acid

 [A] Acidic Nature

Being a very strong acid, it dissociates completely in an aqueous solution.

HNO3 (aq.)                 H+(aq.) + NO3-(aq.)

HNO3 + H2O                            H3O+ + NO3-

Action on bases: HNO3, neutralizes bases, forming nitrate salts.

KOH + HNO3             KNO3 + H2O

CuO + 2 HNO3           Cu(NO3)2  + H2O

NH3 + HNO3                            NH4NO3

Action with carbonates and bicarbonates: HNO3, liberates CO2 gas in reaction with metal carbonates and bicarbonates.

            CaCO3 + 2 HNO3                   Ca(NO3)2 + H2O + CO2

Action with highly electropositive metals: Very dilute HNO3 reacts with only Mg and Mn to produce salt and hydrogen gas.

            Mn + very dil. HNO3             Mn(NO3)3 + H2

The hydrogen gas produced is not pure; it is accompanied to some extent by gaseous reduction products of acids (i.e. NO, NO2 etc.).

16.   Write the name of two metals that can liberate hydrogen gas from HNO3.      2

17.   Write the action of dilute nitric acid upon Mg.                            1

18.   What happens when dilute nitric acid reacts with Mg?                     3

19.   Give the action of dilute and very dilute nitric acid on the magnesium metal. 1

20.   Give a balanced chemical equation for the reaction of conc. nitric acid with Mg.             2

[B] Oxidising Nature

Nitric acid is a very good oxidizing agent because it decomposes to yield nascent hydrogen.

1.       Action on metals:

This reacts with almost all metals even with some which lie below hydrogen in the electrochemical series, except noble metals like Pt and Au.

The reactions with active metals are balanced by the nascent hydrogen formation method in the partial equation method.

a.       Action with Zn

·         With conc. HNO3

2HNO3 + Zn               Zn(NO3)2 + 2 [H]

{HNO3 + [H]               NO2 + H2O } × 2

Zn + 4 HNO3              Zn(NO3)2 + 2NO2 + 2H2O

·         With moderately conc. HNO3 (1:1)

{2 HNO3 + Zn            Zn(NO3)2 +2[H]} x 3 

{HNO3 + 3[H]            NO + 2H2O} × 2

3 Zn + 8 HNO3          3Zn(NO3)2 + 2NO + 4 H2O

·         With dilute HNO3

{2HNO3 + Zn            Zn(NO3)2 +2[H]}×4

2HNO3 + 8[H]           N2O + 5H2O

4Zn + 10HNO3              4Zn(NO3)2 + N2O + 5H2O

·         With very dilute HNO3

{2HNO3 + Zn            Zn(NO3)2 +2[H]} ×4

HNO3 +8[H]              NH3 + 3H2O

NH3 +HNO3              NH4NO3

4Zn +10 HNO3                4 Zn(NO3)2 + NH4NO3 + 3H2O

b.      Action with Fe

·         Highly concentrated nitric acid renders iron passive due to the formation of a layer of ferroso-ferric oxide Fe3O4. This phenomenon is used to prevent rusting of iron.

 

·         With moderately conc. HNO3 (1:1)

Fe + 3 HNO3               Fe(NO3)3 + 3 H

{HNO3 + [H]               NO2 + H2O} × 3

Fe + 6HNO3                Fe(NO3)3 + 3NO2 +3H2O

·         With very dilute HNO3

Fe + 2 HNO3               Fe(NO3)2 + 2 [H]} × 4

HNO3 + 8 [H]             NH3 + 3 H2O

NH3 + HNO3              NH4NO3

4 Fe + 10 HNO3          4 Fe(NO3)2 + NH4NO3 +3 H2O

c.       Action with Cu

·         Conc. HNO3 gives NO2 gas

2 HNO3                             2 NO2 +H2O + [O]

Cu+O                                CuO

CuO + 2 HNO3                 Cu(NO3)2 +H2O

 


Cu +4HNO3                     Cu(NO3)2 + H2O + 2NO2

·         (1:1) HNO3 gives NO gas.

2 HNO3                             2 NO +H2O + 3[O]

[Cu+ [O]                           CuO    ] x 3

[CuO +2 HNO3                Cu(NO3)2 +H2O ] x 3

 


3 Cu + 8 HNO3                 3 Cu(NO3)2 + 4 H2O + 2 NO

2.      Action on Non-metals

Hot and conc. nitric acid oxidizes many nonmetals like carbon, sulphur, phosphorous, iodine etc. to form their oxides or oxyacids.

a.       With carbon (C is oxidized to carbonic acid)

{2 HNO3                                           2 NO2 + H2O + [O] }x 2

C + 2 [O]                     CO2

CO2 + H2O                  H2CO3

C + 4 HNO3                H2CO3 + 4 NO2 + H2O

b.      With sulphur (S is oxidized to sulphuric acid)

2 HNO3                                             2 NO2 + H2O + [O]

S + [O]                         SO2

SO2 + H2O + [O]         H2SO4

S + 6 HNO3                 H2SO4 + 6 NO2 + 2H2O

3.      Action on Reducing compounds

a.       It oxidises H2S to sulphur

2 HNO3                                             2 NO2 + H2O + [O]

H2S + O                       H2O + S

2HNO3 + H2S             2NO2 + 2H2O + S

b.      It oxidises SO2 to H2SO4

2 HNO3                                             2 NO2 + H2O + [O]

SO2 + O                       SO3

SO3 + H2O                   H2SO4

SO2 +2 HNO3             H2SO4 + 2 NO2

c.       It oxidises ferrous salt to ferric salts in presence of conc. Sulphuric acid.

2 HNO3                                                                     2 NO + H2O + 3 [O]

{2 FeSO4 + H2SO4 +O              Fe2(SO4)3 + H2O} x 3

6 FeSO4 + 3 H2SO4 + 2 HNO3     3 Fe2(SO4)3 + 2 NO + 4 H2O

(Practice writing all these reactions a number of times. These are very important)

17.    When HNO3 reacts with metals, NO2 is usually evolved if the acid is

a.       Concentrated                       c. moderately concentrated

b.       Dilute                                     d. very dilute

18.    The reaction of zinc with very dilute HNO3 leads to the formation of

a. N2O5                   b. N2O                    c. NH4NO3              d. NH4NO2

19.    Aqua fortis is a common name for

a.       H2SO4                    b. HCl                      c. HNO3                           d. H3PO4

20.    The metal which evolves hydrogen on reacting with cold dilute HNO3 is

a.       Mg                  b. Al                        c. Fe                        d. Cu

21.    Hydrogen is evolved by the action of cold dilute HNO3 on

a.       Fe                    b. Mg or Mn          c. Ca                        d. Al

22.    Hydrogen is evolved by the action of cold dilute HNO3 on

a.       Al                    c. Cu                       b. Mn                      d. Fe

23.    When zinc reacts with cold and dilute nitric acid it produces

a.       NO                  b. NO2                               c. NH4OH               d. H2

 

21.   What happens when conc. nitric acid is exposed to light for a long time?

22.   Why is conc. nitric acid stored in a dark brown bottle?                    2

23.    Conc. HNO3 decomposes in presence of sunlight by evolving NO2 gas as,

4 HNO3                                  4 NO2 + 2 H2O + O2

24.   How does nitric acid react with Zn?                                                2

25.   How does conc. Nitric acid react with zinc?                                    1

26.   How does nitric acid react with Fe?                                                2

27.   What is the action of HNO3 on Fe?                                                 1

28.   Write the action of conc. nitric acid upon iron.                                1

29.   What happens when the iron is treated with highly conc. nitric acid? 1

30.   Give a balanced chemical equation for the reaction of conc. nitric acid with Cu.         1

9.4.6 Ring Test of Nitrate Ion

For the test of nitric acid or nitrate ion in salt, the solution is first mixed with an equal volume of conc. H2SO4 in a test tube. The solution is cooled under tap water and freshly prepared FeSO4 solution is added slowly from the wall of the test tube, tilting the test tube. The formation of a brown ring confirms the presence of nitrate ion or nitric acid in the solution.

            NO3- + H2SO4                          HNO3 + HSO4-

2 HNO3 + 6 FeSO4 + 3 H2SO4             3 Fe2(SO4)3 + 4 H2O + 2 NO

            FeSO4 + NO                            FeSO4.NO

                                                (Nitrosyl ferrous sulphate) Brown ring

31.   How is nitric acid detected in the laboratory?                                  2

32.   How would you test for the NO3- ion in its aqueous solution?           2

33.   In the ring test of nitrate which chemical compound is formed?        2

34.   What happens when a freshly prepared FeSO4 solution is added to an equal-volume mixture of conc. H2SO4 and conc. HNO3?                                                                                 2

35.   What happens when freshly prepared ferrous sulphate is added to the mixture of conc. Nitric acid and conc. Sulphuric acid?                                                                             2

36.   In the ring test of nitrate what chemical compound is formed?         2

 

37.   Write a chemical reaction to show nitric acid contains nitrogen. 2

When copper metal is reacted with nitric acid at high temperatures, brown fumes of NO2 gas are formed which with iron gives ferric oxide and nitrogen gas. This shows that nitric acid contains nitrogen, as copper does not have nitrogen.

Cu + 4 HNO3                                       Cu(NO3)2 + 2 H2O + 2 NO2

6 NO2 + 8 Fe                                        4 Fe2O3 + 2 N2

 

24.    The nitrogen atom of the compound which has an incomplete octet is

a.       NH4NO3          b. N2O                    c. NO                      d. N2O4

25.    Ammonia can be dried by passing over

a.       CaCl2               b. CaO                    c. P2O5                   d. H2SO4

26.    FeSO4 forms a brown ring with

a.       N2O                 b. NO2                               c. NO                      d. NO3

27.    The brown ring formed in the ring test of nitrate is

a.       FeSO4             c. Fe2(SO4)3                 c. NO2                               d. FeSO4. NO

 

*** This is not a complete note. It is just to guide you. It is recommended to study prescribed textbooks along with this material. ***

 

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posted by Subarnam Oli @ March 23, 2023   0 Comments

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