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Physical Chemistry

Language of Chemistry Stoichiometry Atomic Structure Oxidation and Reduction Periodic Table Acid and Base Electronic Theory of Valency Equivalent Weight and Atomic Weight

Physical Chemistry-II

Non-Metals

Introduction Halogens Nitrogen Sulphur Oxygen

Inorganic Chemistry

Nitrogen

Introduction:

Derived from "Nitre".
Discovered by Daniel Rutherford.
Atomic number=7
Atomic mass = 14 amu.
Diatomic molecule $(N_{2})$ .
Valency=3.
Isotopes: $_{7}^{14} N$ , $_{7}^{15} N$ .
Present in $V A$ in periodic table. $V A$ elements are called pnicogens and their compounds are called pnictides.
Electronic Configuration: $n s^{2} n p^{3}$ .
Nitrogen shows anomalous behaviour. Reasons:

i) Small Size

ii) high value of electronegativity.

iii) non-availability of d-orbitals.

iv) ease of multiple bond formation.

Occurrence

-It is present in air.

-It occurs as Nitrates $N a N O_{3}$ (Chile Saltpetre) and $K N O_{3}$ (Salt petre).

-Present in the form of Protein.

Difference between Nitrogen and other elements of group $V A$ :

$N_{2}$ is gas while others are solid.
$N_{2}$ is diatomic while others are tetra atomic $(P_{4}, A s_{4}, S b_{4})$ except Bismuth $(B i)$ .
$N H_{3}$ forms $H -$ bonding while $P H_{3}$ (Phosphine), $A s H_{3}$ (Arsine), etc do not form H-bond.
Nitrogen is relatively inert among its members of family.
Nitrogen shows wide range of oxidation states $(- 3$ to $+ 5)$ .

Preparations of Nitrogen:

1) By heating ammonium nitrate or ammonium dichromate:

$N H_{4} Cl + N a N O_{2} ⟶ N H_{4} N O_{2} + N a Cl$

$N H_{4} N O_{2} ⟶ N_{2} + H_{2} O$

2) By heating urea with Nitrous acid or alkaline hypobromide:

$N H_{2} CON H_{2} + H N O_{2} ⟶ C O_{2} + 3 H_{2} O + 2 N_{2}$

3) By oxidation of $N H_{3}$ :

$N H_{3} + C l_{2} ⟶ N_{2} + N H_{4} Cl$

4) When sodium or barium azide is heated in small quantity then pure Nitrogen is obtained.

$N a N_{3} ⟶ N a + N_{2}$

Note: $N_{2}$ is manufactured by Fractional Distillation Method.

Properties of Nitrogen:

Physical:

- It is colourless, tasteless and odourless.

- Due to it’s triple bond heat of dissociation is very large.

Chemical:

1) With oxygen:

-The cycle of nitrogen is called nitrogen cycle.

$p ro t e in ⟶ d eco m p . amm o ni u m co m p o u n d ⟶ ba c t er ia N_{2}$

-This process is called denitrification.

2) Reaction with metals:

$4 L i + N_{2} ⟶ 2 L i_{2} N$

3) With Calcium Carbides:

$C a C_{2} + N_{2} ⟶ C a C N_{2} + C$

Uses

-Used in manufacture of $N H_{3}, H N O_{3}, C a C N_{2}$ etc.-Used in filling electric bulb because of it’s inert nature.

Oxides of Nitrogen

1) $NO$ – Nitric Oxide

-It is odd electron molecule $(11)$ .

- It is paramagnetic in nature and is diamagnetic in liquid and solid due to formation of dimer $(N_{2} O_{5})$ .

2) $N O_{2}$ –Nitrogen Dioxide

-Colour: Orange

-Value of $ONO$ angle is 134 $^{\circ}$ .

-It is also paramagnetic in nature.

3) $N_{2} O$ –Dinitrogen Oxide

- It is also called laughing gas.

- It is soluble in water but not in hot water.

4) $N_{2} O_{3}$ – Dinitrogen Trioxide

- Also called nitrogen sesquioxide or nitrogen anhydrite.

5) $N_{2} O_{5}$ –Dinitrogen Pentoxide

-It is ionic solid in solid state but asymmetrical molecule in vapour state.

Compounds of Nitrogen

1)Ammonia $(N H_{3})$ :

Lab preparation

-When ammonium salt is heated with a base then ammonium gas is obtained in lab.

$N H_{4} Cl + C a (O H)_{2} ⟶ C a C l_{2} + 2 H_{2} O + 2 N H_{3}$

Note : It can also prepared by the action of $M e t a ll i c N i t r i d e$ and $Wa t er$ .

$M g_{3} N_{2} + 6 H_{2} O ⟶ 3 M g (O H)_{2} + 2 N H_{3}$

-Obtained gas is dried by passing through quick lime $(C a O)$ and collected in an inverted in gas jar by the downward displacement of air.

Manufacture of Ammonia

Ammonia gas can be manufactured by following process :

1) Haber’s process

$N_{2} + H_{2} 250 a t m; 45 0^{\circ} ⟶ F e / MO 2 N H_{3} + 22.4 Kc a l$

2) Cyanamide $(C a C N_{2})$ process

$C a C_{2} + N_{2} ⟶ 10 0^{\circ} C a C N_{2} + C$

$C a C N_{2} + 3 H_{2} O ⟶ C a C O_{3} + 2 N H_{3}$

3) Serpeck’s process

$A l_{2} O_{3} + 3 C + N_{2} ⟶ 2 A lN + 3 CO ↑$

$A lN + 3 H_{2} O ⟶ A l (O H)_{3} + N H_{3}$

Properties of Ammonia:

Physical Properties:

- It has pungent smell.

- It is highly soluble in water giving an alkaline solution.

- It is also called tear gas.

-The liquid ammonia boils at $- 3 3^{\circ} C e l s i u s$ and freezes at $- 77. 8^{\circ} C e l s i u s$ .

Chemical Properties:

1) Basic Nature

$N H_{3} + H Cl ⟶ N H_{4} Cl$

$N H_{3} + H_{2} O ⇌ N H_{4}^{+} + N H_{2}^{-}$

2) Self-ionization

$N H_{3} + N H_{3} ⇌ N H_{4}^{+} + N H_{2}^{-}$

3) $N H_{3}$ acts as Lewis base.

4) Reaction with alkali metals.

- $N a, K$ can displace $H_{2}$ from ammonia.

$N H_{3} + N a ⟶ N a N H_{2} + H_{2}$

5) With $O_{2}$

- $N H_{3}$ oxidized to $N_{2}$ .

- $N H_{3}$ is catalytically oxidized to $NO$ .

$4 N H_{3} + 3 O_{2} ⟶ △ 2 N_{2} + 6 H_{2} O$

$4 N H_{3} + 5 O_{2} ⟶ △ 4 NO + 6 H_{2} O$

6) With $C O_{2}$

$2 N H_{3} + C O_{2} p ress u re ⟶ 20 0^{\circ} N H_{2} - CO - N H_{2} + H_{2} O$

7) Test reaction:

a) using Nessler’s reagent $(K_{2} H g I_{4})$

b) With Mercurous Nitrate paper $(H g_{2} (N O_{3})_{2})$

Uses:

Used to manufacture urea, nitric acid and used as refrigerant.

Test of Ammonia

1) It gives yellow ppt with chloroplatinic acid $(H_{2} PtC l_{6})$ .

2) $H N O_{3}$ ( Nitric Acid)

Lab Preparation

-When sodium nitrate is heated with $co n c . H_{2} S O_{4}$ in a glass retort nitric acid is obtained.

$N a N O_{3} + co n c . H_{2} S O_{4} ⟶ N a_{2} S O_{4} + 2 H N O_{3}$

Manufacture

1) Ostwald process:

-Catalyst used is $pt$ at $80 0^{\circ} C e l s i u s$ .

$N H_{3} + S O_{2} 80 0^{\circ} ⟶ pt NO + O_{2}$

$2 NO + O_{2} ⟶ 2 N O_{2}$ $3 N O_{2} + H_{2} O ⟶ H N O_{3}$

2) Brikland-Eyde process

$N_{2} + O_{2} ⟶ 2 NO$

$2 NO + O_{2} ⟶ 2 N O_{2}$

$3 N O_{2} + H_{2} O ⟶ 2 H N O_{3} + NO$

$2 N O_{2} + H_{2} O ⟶ H N O_{3} + H N O_{2}$

$H N O_{2} ⟶ H N O_{3} + 2 NO + H_{2} O$

Properties of Nitric acid

Physical properties

-It’s b.p is $84. 1^{\circ} C$ and F.P is $- 4 2^{\circ} C$ .-It is colourless liquid.

Chemical properties:

1) Action on metal:

a) $M g$ :

$M g + d i l . H N O_{3} ⟶ M g (N O_{3})_{2} + H_{2}$

$M g + co n c . H N O_{3} ⟶ M g (N O_{3})_{2} + NO$

Note : Similar reaction with $M n$ .

b) $C u$ :

i) $C u$ with $co l d an d d i l . H N O_{3}$ gives $N_{2} O$ .

ii) $C u$ with $h o t an d d i l . H N O_{3}$ gives $NO$ .

iii) $C u$ with $h o t an d co n c . H N O_{3}$ gives $N O_{2}$ .

Note : $S i l v er$ , $L e a d$ and $B i s m u t h$ also react with $N i t r i c a c i d$ in same manner.

But $H g$ gives $M erc u ro u s$ $ni t r a t e$ with $d i l . H N O_{3}$ .

c) $Z n$ :

i) $Z n$ reacts with $v ery d i l . H N O_{3}$ gives $N H_{4} N O_{3}$ .

$4 Z n + 10 (v ery d i l .) H N O_{3} ⟶ 4 Z n (N O_{3})_{2} + H_{2} O + N H_{4} N O_{3}$ ii) $Z n$ react with $d i l . H N O_{3}$ gives $N_{2} O$ .

$4 Z n + 10 d i l . H N O_{3} ⟶ 4 Z n (N O_{3})_{2} + 5 H_{2} O + N_{2} O$

iii) With $co n c . H N O_{3}$ gives $N O_{2}$ .

$Z n + 4 co n c . H N O_{3} ⟶ 4 Z n (N O_{3})_{2} + 2 H_{2} O + 2 N O_{2}$

Note: $F e$ and $S n$ react with $H N O_{3}$ in same manner.

d) $A g$ :

i) $A g + d i l . H N O_{3}$ gives $NO$ .

ii) $A g + co n c . H N O_{3}$ gives $N O_{2}$ .

To Summarize:

i) Generally $M e t a l$ with $C o n c . H N O_{3}$ gives $N O_{2}$ .

Exception: $H g$ ang $M g$ gives $NO$ .

ii) $Z n (w i t h d i l .), C u (w i t h co l d an d d i l .), F e (w i t h d i l .)$ gives $N_{2} O$ .

iii) $C u (w i t h h o t an d d i l .), P b (w i t h d i l .), H g (w i t h d i l .), A g (w i t h d i l .)$ give $NO$ .

Exception: $H g an d M g (w i t h co n c .)$ give $NO$ .

iv) $Z n, S n w i t h v ery d i l$ give $N H_{4} N O_{3}$ .

v) $M g w i t h d i l . H N O_{3}$ give $H_{2}$ .

5) $H N O_{3}$ also oxidizes with non metals, metalloids and compounds.

$H 2 S ⟶ NO$

$S O_{2} ⟶ NO$

6) Oxidizes Sugar $(C_{1} 2 H_{2} 2 O_{11})$ into Oxalic acid and gives $N O_{2}$ .

Uses :

-To prepare explosives, dyes, drugs, fertilizers.

-Used in purification of gold and Silver, Nitration of Organic compounds.