NITROGEN AND ITS COMPOUNDS at a glance

NITROGEN

Nitrogen occurs mainly as a free element in the air/ atmosphere, about 78% by volume of the atmosphere. It also found in the combined state in many compounds such as ammonia, urea, proteins and trioxonitrates (V) salts. it does not exhibit allotropy and is a diatomic gas 

LABORATORY PREPARATION

From Air

It can be prepared from air by first passing air through caustic soda to remove CO₂ and then over heated copper turnings to remove and O₂ [ the oxygen can equally be removed by passing the air through alkaline pyrogallol]. The nitrogen obtained is not pure and is denser than air because it contains about 1% by volume of rare/ noble gases.

Pure nitrogen is obtained in the laboratory by any of the following method below:

1.  Thermal decomposition of ammonium dioxonitrate (III)

a.  NaNO_2(aq) + NH₄Cl_(aq) → NH₄NO_2(aq) +NaCl_(aq)

b. NH₄NO_2(aq) →2H₂O_(l) + N_2(g)              

2.       Thermal decomposition of ammonium heptaoxodichromate (VI)

                       (NH₄)₂Cr₂O_7(s) → Cr₂O_3(s) + 4H₂O_(l) + N_2(g)

3.       Oxidation of ammonia by hot Copper (II) oxide

                        2NH_3(g)+3CuO_(s) → 3Cu_(s) + 3H₂O_(g)+ N_2(g)

4.             Reduction of dinitrogen (I) oxide by red-hot copper.

N2O_(g) + Cu_(s) → CuO_(s) + N_2(g)

INDUSTRIAL PREPARATION

Industrially, nitrogen is obtained by fractional distillation of liquid air.  (see industrial preparation of Oxygen)

PHYSICAL PROPERTIES

1.         It is colourless gas.

2.          It is an odourless.

3.          It is a  tasteless

4.         Pure nitrogen is lighter than air.

5.         Slightly soluble in water

6.         Melting point -210⁰C and   boiling point is -196⁰C

CHEMICAL PROPERTIES

1.       It reacts with very electropositive metals to form nitrides

      3Mg_(s) + N_2(g) → Mg₃N_2(s)

2.       It reacts with non – metals like hydrogen and oxygen to form ammonia and oxides respectively.

     N_2(g)+ 3H_2(g) → 3NH_3(g)

                 N_2(g) + 2O_2(g) → 2N₂O_(g)

USES

1.       It is used industrial manufacture of ammonia.

2.       Liquid nitrogen is used as a cooling agent.

3.       It is used as preservative in packaged foods to prevent rancidity.

The stages in which nitrogen from the atmosphere is converted into soil nitrogen and back to atmospheric nitrogen is summarized below.

1.   Oxidation of atmospheric nitrogen:

N_2(g) + O_2(g) →2NO_(g)

2NO_(g) + O_2(g)→ 2NO_2(g)

4NO_(g)+O_2(g)+2H₂O_(l)→4HNO_2(q)

 4NO_(g)+O_2(g)+2H₂O_(l)→4HNO_3(aq)

2.   Action of nitrogen-fixing bacteria: 

3. Nitrification by nitrifying bacterial.

4. Denitrification by denitrifying bacteria 

COMPOUNDS OF NITROGEN

OXIDES OF NITROGEN

1. NITROGEN (I) OXIDE, N₂O

Nitrogen (I) oxide also known as laughing gas. (it can cause uncontrollable laughter when inhale).

LABORATORY PREPARATION

It is prepared in the lab by thermal decomposition of ammonium trioxonitrate (V). Ammonium trioxonitrate (V) can not heated directly because the reaction being highly exothermic and may become uncontrollable leading to an explosion. 

a.  KNO_3(s) + NH₄Cl_(s) → KCl_(s) + NH₄NO_3(s)

b  NH₄NO_3(s) → 2H₂O_(g) + N₂O_(g)

PHYSICAL PROPERTIES

1.    It is a colourless gas 

2.   It has faintly sickly sweet smell.

3.      It has a sweetish taste.

4.  It is fairly soluble in cold water.

6.   It is a neutral gas

CHEMICAL PROPERTIES

1.       It decomposes on strong heating to form nitrogen and oxygen.

      2N₂O_(g)→ O_2(g)+2N_2(g)

2.     It  burns in any  substance which is hot enough to decompose it.

    Mg_(s)+ N₂O_(g)→ MgO_(s)+ N_2(g)

3. it is reduced to nitrogen when in contact with very hot iron or copper. 

 Cu_(s) + N₂O_(g)→ N_2(g)+ CuO_(s)

TEST FOR N₂O

When a glowing splinter is inserted into the jar containing the unknown gas and it  rekindles, then the gas is either oxygen or nitrogen (I) oxide. If the gas has a pleasant smell and does not produce brown fumes of nitrogen (IV) oxide when burnt in air; then the gas is nitrogen (I) oxide.

USE: Nitrogen (I) oxide is used as anesthetic for minor surgical operations.

NITROGEN (II) OXIDE, NO

LABORATORY PREPARATION

Nitrogen (II) oxide is prepared by reacting combining copper with 50% trioxonitrate (IV) acid.

3Cu_(s) + 8HNO_3(aq)→ 3Cu(NO₃)_2(aq)+ 4H₂O_(l) + 2NO_(g)

 brown fumes of nitrogen (IV) oxide produced by some of the nitrogen (II) oxide as they react with oxygen is removed as the gas is pass through water.

PHYSICAL PROPERTIES

1. It is a colourless gas 

2. It is a poisonous gas.

3.  It is a sp7aringly soluble in water.

3.  It is slightly denser than air.

4.  It is neutral to litmus.

CHEMICAL PROPERTIES

1.  It combines readily with oxygen to form brown fumes of nitrogen (IV) oxide

         2NO_(g) + O_2(g) → 2NO_2(g)

2.   At high temperature, it decomposes to form equal volume of nitrogen and oxygen

         2NO_(s)→ N_2(g) + O_2(g)

3.   It is reduced to nitrogen by hot metals

 2Cu_(s)+ 2NO_(g) → 2CuO_(g) + N_2(g)

4.  It decolourizing acidified potassium tetraoxomanganate (VI) slowly ( reducing agent)

3MnO₄^-_(aq)+ 4H⁺_(aq) + NO_(g)→3Mn²⁺_(aq) 5NO₃^-

Test for NO

1. With acidified  iron (II) tetraoxosulphate (VI): A solution of acdified FeSO₄ is poured into the gas jar containing the unknown gas. If the solution turns dark brown, then the gas is NO.

NITROGEN (IV) OXIDE, NO₂

LABORATORY PREPARATION

It is prepared by thermal decomposition of lead (II) trioxonitrate (V) Pb(NO3)2. 

Pb(NO3)2 is preferred because it does not contain water of crystallization which can interfere with the preparation.

          

Dig

Pb(NO₃)_2(s) → 2PbO_(s) + O_2(g)+ 4NO_2(g)

The gaseous mixture obtained is passed through a U- tube dipped in ice, Nitrogen (IV) oxide liquefies as a green liquid (yellow if pure) in the tube while oxygen escapes out.

PHYSICAL PROPERTIES

1.  It is a reddish – brown gas.

2.  It has an irritating smell 

3. It  is a poisonous gas 

4.  It liquefies into yellow liquid at 21^oC.

5.  It is denser than air.

CHEMICAL PROPERTIES

1. It turns damp blue litmus paper red

2.  Nitrogen (IV) oxide exists mainly as dinitrogen (IV) oxide, N₂O₄ at low temperature. It decomposes on heating as follows.

N₂O_4(g) + 2O_2(g) → 2NO2_(g) + O_2(g)

•  Pale                    Reddish         
•  yellow                 brown                 

2.     It decomposes on heating to nitrogen and oxygen and so supports combustion 

  2NO_2(g) → N_2(g)+ 2O_2(g)

3.  With reducing agents it is reduced to nitrogen.

  4Cu_(s) + NO2 → 4CuO_(s) + N_2(g)

4.  With dissolved in water it forms two acids, dioxonitrate (III) and trioxonitrate (V) acids, hence, It is a mixed acid anhydride.

  H₂O_(l)+ 2NO_2(g) → HNO_2(aq)+ HNO_3(aq)

5.  It reacts with alkalis to form a mixture of dioxonitrate (III) and trioxonitrate (V) salts

  2KOH_(aq)+ 2NO_2(g) → KNO_3(aq) + KNO_2(aq) + H₂O_(l)

AMMONIA

Ammonia is a hydride of nitrogen. It is found in traces in the atmosphere from the decomposition/ decay of nitrogenous matter in the absence. Because is very soluble in water, it dissolves in rainwater and is washed down into the soil.     

LABORATORY PREPARATION OF AMMONIA

Ammonia is prepared in the laboratory by heating calcium hydroxide, Ca(OH)₂ (slaked lime) with ammonium chloride.

Ca(OH)_2(s)+ 2NH₄Cl_(s)→CaCl_2(s) +2H₂O_(l)+2NH_3(g).

It is dried using calcium oxide, CaO. Because it will react with drying agents like Conc. H₂SO₄ or fused CaCl₂, since it is an alkaline gas.

            

INDUSTRIAL PREPARATION

Ammonia is manufactured by the Haber process from nitrogen and hydrogen. In this process  nitrogen and hydrogen are reacted  in ratio 1:3 by volume. The reaction is reversible. The conditions for optimum yield of ammonia are 

i. A temperature of 450^Oc 

ii. A pressure of about 200atm and 

iii. Finely divided iron catalyst   

N_2(g) +3H_2(g) →2NH_3(g) + heat

PHYSICAL PROPERTIES

i.   It is a colorless gas 

ii. It has  a characteristic choking/ pungent smell.

iii. When inhaled in large quantity it is poisonous 

3. It is the only known alkaline gas.

4. It is about less dense than air.

CHEMICAL PROPERTIES

1. Ammonia burns readily in oxygen to yield and nitrogen and water vapour 

 4NH_3(g)+3O_2(g)→6H₂O_(g)+ 2N_2(g)

2. As a reducing agent, it reduces most metallic oxides to their metals. 

 i. 3CuO_(s) + 2NH_3(g) → 3Cu_(s) + 3H₂O_(l) + N_2(g)

ii.   With Chlorine it yields NH4Cl

  3Cl_2(g) + 8NH_3(g) → 6NH₄Cl_(s) + N_2(g)

3.  Ammonia reacts with carbon IV oxide to form Urea and water vapour.

 2NH_3(g)+ CO_2(g) → (NH₂)₂CO_(s) + H₂O_(l)

                        ^urea

4. With acids it form ammoniums salts.  

 2NH_3(g) + H₂SO_4(g)→(NH₄)₂SO_4(s)

TEST FOR AMMONIA

Ammonia has a choking and a pungent smell. It can be confirmed using:

1. Litmus paper: It turns damp red litmus paper blue

2.  Hydrochloric acid: it forms dense white fumes with a concentrated on a glass rod 

USES OF AMMONIA

1.  Is is one of the raw materials in the Solvay process for the   manufacture trioxonitrate (V) acid and Sodium trioxocarbonate (IV).

2. Liquid ammonia is used as a refrigerant.

3. Aqueous ammonia is used in softening temporary hard water.

4.    Aqueous ammonia is also used in laundries as a solvent for removing grease and oil stains.

TRIOXONITRATE (V) ACID, HNO₃

LABORATORY PREPARATION

Trioxonitrate (V) acid is a volatile acid. It is prepared in the laboratory by  displacement of the HNO3 from any trioxonitrate salt by concentrated H₂SO₄ which is less volatile. Trioxonitrate (V) of potassium or sodium is usually used because they are cheap.

KNO_3(s)+ H₂SO_4(aq)→ KHSO_4(aq)+HNO_3(aq)

NOTE: we use an  all-glass apparatus for this preparation because the hydrogen trioxonitrate (V) acid vapour will attack cork or rubber.

INDUSTRIAL PREPARATION

It is prepared by the catalytic oxidation of ammonia:

-    Ammonia is treated with excess air using Platinum-rhodium catalyst at 700^oC to produce

4NH_3(g)+ 5O_2(g)→ 4NO_(g)+ 6H2O the nitrogen (II) oxide formed is cooled and mixed with excess air to produce nitrogen (IV) oxide.

2NO_(g) + O_2(g) →2NO₂(g)

-    Nitrogen (IV) oxide formed is dissolved with excess air in hot water to yield trioxonitrate (V) acid solution of up to 50% concentration. 

4NO_2(g)+ 2H₂O_(l)+ O_2(g) → 4HNO_3(aq)

PHYSICAL PROPERTIES

1.  Pure HNO3 acid is a colourless liquid with sharp choking smell. It fumes in air. The acid decomposes to give NO2 gas which redissolves in the acid turning it yellow after a while.

2. The density of the pure acid is 1.52 gcm^-3

3.  The pure acid boils at 86⁰C and melts at -47^oC  

4.   The pure acid dissolves in water in all proportions 

5.  The concentrated form of the acid is corrosive.

CHEMICAL PROPERTIES

1.  As an acid 

I. The dilute acid turns blue litmus red.

 ii.  it neutralizes bases and alkalis to form metallic trioxonitrate (V) and water only

NaOH_(aq)+HNO_3(aq) → NaNO_3(aq)+ H₂O_(l)

iii. it reacts with trioxocarbonate (IV) to liberate carbon (II) oxide 

 CaCO_3(s) + HNO_3(aq) → Ca(NO₃)_2(aq)+ H₂O_(l)+ CO_2(g)

3.  Unlike other acids, it rarely gives out hydrogen with metals except when very dilute solution is reacted with Ca, Mg or Mn.

4.    As an oxidizing agent, 

it oxidizes non–metal like Sulphur to form the corresponding oxides of the non – metals.

  S_(s)+ 6HNO_3(aq)→H₂SO_4(aq) + 2H₂O_(l) + 6NO_2(g)

ii.   it oxidizes least reactive metals like Cu, Pb, Hg and Ag to yield the respective trioxonitrate (V) and nitrogen (IV) oxide.  With moderate  concentration  it yields nitrogen (II) oxide.

Aluminum and iron are not oxidized by the acid, because of the  formation of a thin  coating of the oxide on the surface of the metal which is lmpervious to further attack on the metals. 

Hence, containers lined with aluminum and iron can be used to transport concentrated HNO_3(aq)

5.As an oxidizing agent, it oxidizes hydrogen sulphide to sulphur

  H₂S_(g) + 2HNO_3(aq) → S_(s)+ 2H₂O_(l)+2NO_2(g)

6.  it oxidizes iron (II) salts to iron (III) salts

 6Fe²⁺_(aq) + 8H⁺_(aq) + 2NO₃^-_(aq) →   6Fe³⁺_(aq) + 4H₂O_(l) + 2NO_(g)

USES

1.  It is used as an acid, oxidizing agent and nitrating agent in the laboratory.

2. It is as rocket fuel

3. It is used in producing nylon and Terylene.

4.  It is used to produce fertilizers, dyes, drugs and explosives.

OBJECTIVE QUESTIONS 

1.  In which group of the periodic table is nitrogen found? 

(a) 2

 (b) 5 

(c) 7

(d) 6

2. The boiling point of nitrogen in ⁰C is

 (a) -183

 (b) -196

 (c) 200

 (d) 240

3.   The percentage of nitrogen in air is

 (a) 78 

(b) 75 

(c) 71

 (d) 67

4. The following are uses of nitrogen except a. as a cooling agent b. to prevent rancidity c. in the manufacture of fertilizers d. in laundry.

5. The atomicity of nitrogen is 

(a) 1

(b) 2

 (c) 3

 (d) 4

6.  Which of the following compound will leave a metal residue when heated 

a. Cu(NO₃)₂

b. AgNO₃

c. K₂CO₃

4.CaCO₃

7.  The gas given off when NH4Cl is heated with an alkali is 

a. H₂

b. Cl₂

c. N₂ 

d. NH₃

8. 

9. 

10.

11. 

12.

THEORY

 

1a.   State TWO physical properties and TWO chemical properties of nitrogen.

1b   Mention THREE uses of nitrogen.

1c(i) Briefly describe the preparation of nitrogen from air in the laboratory. 

2a(i)   Give an equation to show the laboratory preparation of nitrogen (II) oxide.

2b. Describe a test to distinguish between nitrogen (I) oxide and oxygen gas.                    

2c(iii) Briefly describe the laboratory preparation of ammonia.

3a   State TWO physical and THREE chemical properties each of ammonia.                                       

3b.  Describe the laboratory preparation of trioxonitrate (V) acid.

3c  Write TWO equations of reactions in which trioxonitrate (V) is acting as an acid.

4a. Write an equation to show the reaction of nitrogen (IV) oxide as a mixed anhydride.

4b.  Describe the electrolysis of CuSO₄ solution using platinum electrodes.

4c. Classify the following oxides: CuO, Na₂O, PbO, NO₂, N₂O