‌

Navigation

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

Halogens

Introduction:

Greek word 'Halos': sea salts and 'gen': producer.
Belongs to the group $V II A$ of the periodic table.
Eg: $F, Cl, B r, I$
Astatine is a radioactive element.
Fluorine is the most reactive and called super halogen.
Iodine occurs in petroleum oil.
Outermost configuration is $n s^{2} n p^{5}$ .
Exists as diatomic molecules containing single covalent bonds.
Order of I.E = $F > Cl > B r > I$ .
Order of Electro-negativity = $F > Cl > B r > I$ .
Order of Electro-affinity = $Cl > F > B r > I$ .
Order of Reactivity = $F_{2} > C l_{2} > B r_{2} > I_{2}$ .
Oxidizing Power= $F_{2} > C l_{2} > B r_{2} > I_{2}$ .
Order of Melting point= $F_{2} < C l_{2} < B r_{2} < I_{2}$ .
Order of Atomic Radii= $F_{2} < C l_{2} < B r_{2} < I_{2}$ .
Order of Bond dissociation energy= $C l_{2} > B r_{2} > F_{2} > I_{2}$ .
They occur in combined form.
State: $F_{2}$ and $C l_{2}$ =Gases, $B r_{2}$ =Liquid and $I_{2}$ =Solid.

$C a F_{2}$ = Fluospar

$N a Cl$ =Rock salt

$K Cl$ = Slyvine

$K Cl . M g C l_{2} .6 H_{2} O$ =Carnalite

$N a_{3} A I F_{6}$ = Cryolite

$N a I O_{3}$ =Caliche

Oxidation state

-varies from $- 1$ to $+ 7$ .- $Cl$ form most no. of oxides. $C l_{2} O > Cl O_{2} > C l_{2} O_{6} > C l_{2} O_{7}$

Least stable = $F_{2}$ (Super Halogen).
Most stable = $I_{2}$

Preparation of Halogens:

$F_{2}$ =It can only prepared by electrolytic oxidation of $F^{-}$ but not by chemical oxidation.

i.e. By electrolysis of $H F$ in presence of $K F$ .

$KH F_{2} \to H F + K F$

$K F ⇌ K^{+} + F^{-}$

$H F ⇌ H^{+} + F^{-}$

At Cathode: $2 H^{-} + 2 e^{-} \to H_{2} ↑$

At Anode: $2 F^{-} - 4 e^{-} \to 2 F_{2} ↑$

General Preparation of $C l_{2}, B r_{2},$ and $I_{2}$ .

-These are prepared by heating $N a X$ with Conc.H2SO4 and $M n O_{2}$ .

$N a X + co n c . H_{2} S O_{4} \to △ N a H S O_{4} + H X] \times 2$

$M n O_{2} + C o n c . H_{2} S O_{4} \to △ M n S O_{4} + H_{2} O + [O]$

$[O] + 2 H X \to △ H_{2} O + X_{2}$

Overall:

$2 N a X + M n O_{2} + 3 co n c . H_{2} S O_{4} \to 2 N a H SO 4 + M n SO 4 + 2 H_{2} O + X_{2}$

Preparation of $C l_{2}$ without heating :

For this $K M n O_{4}$ is treated with $co n c . H Cl$ .

$2 K M n O_{4} + 16 co n c . H Cl \to 2 K Cl + M n C l_{2} + 8 H_{2} O + 5 C l_{2}$

Manufacture of Bromine using Carnalite:

-Carnalite is double salt of $K Cl . M g Cl .6 H_{2} O$ and it contains impurities $K B r$ and $M g B r_{2}$ .

$2 K B r + C l_{2} \to △ B r_{2} + 2 K Cl$

$M g B r_{2} + C l_{2} \to △ B r_{2} + 2 K Cl$

Manufacture of iodine using sea weeds:

-Seas weeds contain impurities $K I$ and $N a I$ .Iodine is obtained by heating these impurities with and $M n O_{2}$ .

$2 K I + M n O_{2} + 3 co n c . H_{2} S O_{4} \to 2 I_{2} + M n S O_{4} + 2 KH S O_{4}$

Preparation of Iodine using chili salt petre.

Chile salt petre $(N a N O_{3})$ contains impurity caliche $(N a I O_{3})$ .

$2 N a I O_{3} + 5 N a H S O_{3} \to 2 N a_{2} S O_{4} + 3 N a H S O_{4} + H_{2} O + I_{2}$

Chemical Properties:

1)Reaction with hydrogen: It gives acid. Eg: $H F, H Cl, H B r, H I$

$H_{2} + F_{2} ⟶ d a r k 2 H F$

$H_{2} + C l_{2} ⟶ l i g h t 2 H Cl$

$H_{2} + C l_{2} ⟶ △ 2 H B r$

$H_{2} + I_{2} ⟶ △ 2 H I$

2)With Metals:

Halogens combine with metal forming their halides.

$N a + C l_{2} \to 2 N a Cl$

3)With non metals:

Halogens combine with non metal forming their halides.

$S + C l_{2} \to S F_{6}$

4)With alkali:

$F_{2} + N a O H co l d ⟶ N a F + O F_{2} + H_{2} O$

$F_{2} + N a O H h o t ⟶ N a F + O_{2} + H_{2} O$

$C l_{2} + N a O H co l d \to N a Cl + N a ClO + H_{2} O$

$C l_{2} + N a O H h o t ⟶ N a Cl + N a Cl O_{3} + H_{2} O$

-Similar reaction with $B r_{2}$ and $I_{2}$ as $C l_{2}$

5) Oxidising Property

a) $F_{2}$ oxidizes $K Cl O_{3}$ to $K Cl O_{4}$ .

b) $H_{2} S$ is oxidized by halogen $S$ .

c) $S O_{2}$ is oxidized to $H_{2} S O_{4}$ .

d) $N a_{2} S O_{3}$ is oxidized to $N a_{2} S O_{4}$ .

e) $F erro u s$ is oxidized to $f err i c$

f) $N a_{2} S_{2} O_{3}$ to $N a_{2} S_{4} O_{6}$ .

6) Reaction of $C l_{2}$ with slaked lime :

$C l_{2} + C a (O H)_{2} co l d ⟶ C a C l_{2} + C a (OCl)_{2} + H_{2} O$

$C l_{2} + C a (O H)_{2} w a r m ⟶ C a OC l_{2} + H_{2} O$

$C l_{2} + C a (O H)_{2} h o t ⟶ C a C l_{2} + C a (Cl O_{3})_{2} + H_{2} O$

Uses:

To sterilize water.
As a bleaching agent.
Iodine to make antiseptic solution.
$C l_{2}$ for the preparation poisonous gases like Phoshene $(COC l_{2})$ ,Mustard gas, Tear gas $(CC l_{3} . N O_{2})$ ,etc.
$C l_{2}$ for preparation of bleaching powder $(C a OC l_{2})$ and the bleaching action of $C l_{2}$ is due to oxidation and is permanent.

Note:

-Carnalite is ore of Mg and is salt of Cl.

-Carnalite is used to manufacture bromine.

Hydrogen Halides

Introduction:

State: $H F$ =Liquid (due to $H -$ bond), $H Cl, H B r & H I$ =Gases.
Colour: Colourless in liquid state and white crystalline in solid state.
Highly soluble in water.
Order of Melting Point: $H F > H I > H B r > H Cl$
Order of Stability: $H F > H Cl > H B r > H I$ .
Order of Ionic character : $H F > H Cl > H B r > H I$ .
Order of Reactivity and reducing action : $H F < H Cl < H B r < H I$ .
Order of Dipole Moment: $H F > H Cl > H B r > H I$ .
Order of Bond Length: $H F > H Cl > H B r > H I$ .
Boiling Point: $H F < H I < H B r < H Cl$

Preparations:

Preparation of $H F$ :

$C a F_{2} + co n c . H_{2} S O_{4} ⟶ H F + C a S O_{4}$

Preparation of $H Cl$ :

$co n c . H_{2} S O_{4} + N a Cl \to H Cl + N a H S O_{4}$ .

-This is also dry test for $C L^{-}$ .

For $H B r$ and $H I$

$N a B r + H_{3} P O_{4} ⟶ H B r + N a_{3} P O_{4}$

$N a I + H_{3} P O_{4} ⟶ H I + N a_{3} P O_{4}$

Note: - $H B r$ and $H I$ can also be prepared by heating Phosphorous, Halogen and Water.

$P + 4 B r_{2} ⟶ △ PB r_{3} + PB r_{5}$

$PB r + 4 H_{2} O ⟶ 3 H B r + H_{3} P O_{4}$

$PB r_{3} + 3 H_{2} O ⟶ 3 H B r + H_{3} P O_{3}$

Chemical Properties:

1)Oxidation by air $H I, H B r$ and $H Cl$ are oxidized to $I_{2}, B r_{2}$ and $C l_{2}$ .

But $H F$ is not oxidized.

2)Reducing character

$H I > H B r > H Cl > H F$

a) With acidified $K M n O_{4}$ :

$2 K M n S O_{4} + H_{2} S O_{4} + H I ⟶ K_{2} S O_{4} + M n S O_{4} + H_{2} O + I_{2}$

b) With acidified $K_{2} C r_{2} O_{7}$ :

$K_{2} C r_{2} O_{7} + H_{2} S O_{4} + H B r ⟶ K_{2} S O_{4} + C r_{2} (S O_{4})_{3} + H_{2} O + B r_{2}$

c) With $co n c . H_{2} S O_{4}$ :

$co n c . H_{2} S O_{4} + H B r ⟶ S O_{2} + H_{2} O + B r_{2}$

3) Test reaction :

Silver Nitrate $(A g N O_{3})$ taste is carried out.

$H F$ = no ppt $H B r$ = Pale yellow ppt

$H Cl$ =White ppt $H I$ = Yellow ppt

Uses:

$H Cl$ :

-Used to make Aqua regia. $(3 co n c . H Cl + co n c . H N O_{3})$

-Used as lab reagent.

$H B r$ :

-used to prepare $A g B r$ $&$ $K B r$ that are used in photography and medicine respectively.

$H I$ :

-Used as reducing agent.

-Used to make $A g I$ for photography.

$H F$ :

-Used to make itching glass

$S i O_{6} + 6 H F ⟶ H_{2} S i F_{6} + H_{2} O$

Oxyacids of Halogens:

Fluorine forms only one oxyacid, hypofluorous acid $(H OF)$ .
Other halogens forms several oxyacids of types.

Types and their oxidation number:

-Hypohalous acid $(H XO)$ = $+ 1$

-Halous acid $(H X O_{2})$ = $+ 3$

-Halic acid $(H X O_{3})$ = $+ 5$

-Perhalic acid $(H X O_{4})$ = $+ 7$

Properties:

Acidic Strength:

i) Same Halogen:

$H Cl O_{4} > H Cl O_{3} > H Cl O_{2} > H ClO$

ii) Different Halogen:

$H OCl > H OB r > H O I$ (electro-negativity decreases order $Cl < B r < I$ )

$H Cl O_{2} > H B r O_{2} > H I O_{2}$

$H Cl O_{3} > H B r O_{3} > H I O_{3}$

$H Cl O_{4} > H B r O_{4} > H I O_{4}$

Thermal Stability of Oxyacid:

$H ClO < H Cl O_{2} < H Cl O_{3} < H Cl O_{4}$

Oxidizing Power:

$H ClO > H Cl O_{2} > H Cl O_{3} > H Cl O_{4}$