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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

Inorganic Chemistry

Introduction Compound of Metals Hydroxide Chlorides And Nitrates Sulphates And Carbonates General Metallurgy Sodium and Its Compounds Copper Zinc Iron

Sodium and Its Compounds

Indroduction:

Sodium is soft, silverly white, highly reactive metal which does not occur free in nature.
To prevent its reaction in the atmosphere, it is kept in kerosene oil.
It can be easily cut with a knife.
It is able to conduct heat and electricity.
It is strongest reducing agent.

Difficulties on Extraction of Sodium:

i) Other agents can't reduce Sodium as it itself is a powerful reducing agent.

ii) Sodium is tarnished in air.

iii) Carbon reduction and hydrogen reduction is not feasible because it reacts with them to form carbide and hydroxide.

Down's electrolytic cell overcome these difficulties and sodium was extracted successfully from molten NaCl.

Extraction of Sodium by Down's Process

Anode:- Graphite (Only $1$ )
Cathode:- Iron ( $2$ cathode)
Sodium is obtained by the electrolysis of $m o lt e n$ $N a Cl$ .
Anode and cathode are separated from each other by a cylindrical steel gauge diaphragm so that $N a$ and $C l_{2}$ are kept apart.
Down's cell consists of a rectangular container of steel.
Inside of the tank is lined with firebricks.
Electrolyte is the mixture of $N a Cl$ and $C a C l_{2}$ in the ratio of $40 : 60$ by mass.
$C a C l_{2}$ is mixed to reduce the melting temperature of NaCl from about $80 0^{.} C - 60 0^{.} C$ $600^{\circ} - 800^{\circ} C$
Therefore, there is chance of reduction of $N a^{+}$ or $C a^{++}$ ions at cathode.
Due to standard reduction potential of Na is greater than that of $C a$ , $N a$ is deposited at cathode.
Fused Sodium Chloride ionizes as:

$N a Cl \to 2 N a^{+} + 2 C l^{-}$

At Cathode:

$2 N a^{+} + 2 e^{-} \to 2 N a (R e d u c t i o n)$

At Anode:

$2 C l^{-} \to C l_{2} + 2 e^{-} (O x i d a t i o n)$

Overall:

$2 N a^{+} + 2 e^{-} \to 2 N a$

$2 C l^{-} \to C l_{2} + 2 e^{-}$

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$2 N a^{+} + 2 C l^{-} \to 2 N a + C l_{2}$

Note: $N a$ is collected in bottle containing Kerosene and $C l_{2}$ is escaped from head.

Chemical Properties of Sodium:

Action with air:

$N a + O_{2} \to N a_{2} O + H_{2} O ⟶ m o i s t u re N a O H + C O_{2} \to N a_{2} C O_{3}$

But in dry air $N a_{2} O$ is only formed

$4 N a + O_{2} \to N a_{2} O$

While burning Na on air, moisture of oxide and peroxide formed

$6 N a + 3 O_{2} \to 2 N a_{2} O + N a_{2} O_{2}$

Reaction with $H_{2} O$ :

$2 N a + 2 H_{2} O \to 2 N a O H + H_{2} + ∆$

$2 H_{2} + O_{2} \to 2 H_{2} O + f l am e$

Reaction with acid:

$2 N a + 2 H Cl \to 2 N a Cl + H_{2}$

Reaction with Alcohol:

$R - O - H + 2 N a \to 2 R - O - N a + H_{2}$

Where, $R = a l k y l g ro u p$ like $C H_{3}, C_{2} H_{5}$

Reaction with Ammonia:

$2 N a + 2 N H_{3} ⟶ △ 2 N a N H_{2} + H_{2}$

Reaction with $C O_{2}$ :

$4 N a + 3 CO 2 ⟶ △ 2 N a 2 CO 3 + C$

Reaction with Reducing agent:

Being strong reducing agent, it reduces $S i O_{2}, B_{2} O_{3}, T i C l_{4}$ , etc.

$4 N a + S i O_{2} ⟶ △ S i + 2 N a_{2} O$

$4 N a + T i C l_{4} ⟶ △ T i + 4 N a Cl$

$6 N a + B_{2} O_{3} ⟶ △ 2 B + 2 N a_{2} O$

Reaction with non-metal:

$2 N a + H_{2} ⟶ △ 2 N a O H$

$2 N a + S ⟶ △ N a_{2} S$

$2 N a + C l_{2} ⟶ △ 2 N a Cl$

$3 N a + P ⟶ △ N a_{3} P$

$6 N a + N_{2} ⟶ △ 2 N a_{3} N$

Uses:

Used in sodium vapor lamps.
Used in Lassaigne's test for detection of foreign element of organic compounds.

Manufacture of Caustic Soda $(N a O H)$

Caster Kellner Process:

Consists of large rectangular tank, divided into three compartments by slate partition, very close to bottom, but not touched with bottom.
In Outer Compartment:

-There are graphite anode and flowing mercury acts as cathode.

-They are filled with saturated brine.

In Middle Compartment:

-There are $I ro n$ as $c a t h o d e$ and flowing $M erc u ry$ acts as $an o d e$ .

Contains $d i l . N a O H$ solution.

The whole cell is pivoted at one end and rests on an eccentric wheel at other end.
On passing electric current the brine is electrolysed on outer compartments.
Chlorine is liberated at anode and Sodium is discharged at mercury cathode forming $N a H g$ .
The eccentric wheel oscillates the cell slowly, thereby bringing amalgam to middle compartment.

$N a H g \to N a + H g (A t A n o d e)$

$H_{2} O \to H^{+} + O H^{-} (i o ni z a t i o n)$

$2 H^{+} + 2 e^{-} ⟶ △ H_{2} (A tC a t h o d e) (L ib er a t e d o u t)$

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$N a^{+} + O H^{-} \to N a O H$

When Solution in inner compartment is sufficiently concentrated (about $20 %$ ), it is drawn out and evaporated to dryness.

Purification:

-Unlike $N a$ (By Down's process which is almost $100 %$ pure), NaOH contains some $N a_{2} C O_{3}$ , by reaction with $C O_{2}$ in air, which is made pure by dissolving in alcohol, which is finally removed by filtration.

Kellner Solvay Method:

In this manufacture process, sodium chloride (saturated brine) is electrolysed and discharged in flow of mercury to form sodium amalgam in upper tank and brought it to lower tank where it is hydrolysed to form sodium hydroxide.
It has a bunch of carbon anode and flowing mercury acts as mercury cathode in upper tank.
Brine solution is solution of $N a Cl$ with $H_{2} O$ , so it contains $N a^{+}, C l^{-}, H^{+}, O H^{-}$ ions.
On electrolysis $C l^{-}$ and $H^{+}$ ions are discharged leaving $N a^{+}, O H^{-}$ ions, i.e. components of $N a O H$

In Upper Tank:

- $N a Cl ⇌ N a^{+} + C l^{-}$

At Cathode:-(Reduction)

$2 N a^{+} + 2 e^{-} \to 2 N a$

$2 N a + 2 H g \to 2 N a H g$

At Anode:-(Oxidation)

$2 C l^{-} - e^{-} \to 2 Cl \to C l_{2} (re m o v e d f ro m o u tl e t)$

In Lower tank:

-Hydrolyzation of Sodium Amalgam

$2 N a H g + 2 H_{2} O \to 2 N a O H + H_{2} ↑ + 2 H g$

-The regenerated mercury is recirculated in upper tank (in mercury reservoir)

Manufacture of Sodium Carbonate (Na₂CO₃)

-Sodium Carbonate generally known as washing soda, has manufacture principle as CO₂ is bubbled on brine solution saturated with ammonia sodium bicarbonate is formed which on heating gives washing soda.

$N H_{3} + H_{2} O + C O_{2} ⟶ △ N H_{4} H C O_{3}$

(sufficient amount of $C O_{2}$ )

$N H_{4} H C O_{3} + N a Cl ⟶ △ N H_{4} Cl + N a H C O_{3}$

$2 N a H C O_{3} ⟶ △ N a_{2} C O_{3} + C O_{2} ↑ + H_{2} O$

Details:

i) Saturation of brine with ammonia:

- $N H_{3}$ gas is mixed with little $C O_{2}$ (from ammonia recovery tower).

-Any $M g$ or $C a$ salts present are precipitation.

$2 N H_{3} + C O_{2} + 2 H_{2} O \to (N H_{4})_{2} C O_{3}$

$C a C l_{2} + (N H_{4})_{2} C O_{4} \to C a C O_{3} + 2 N H_{4} Cl$

$M g C l_{2} + (N H_{4}) C O_{3} \to M g C O_{3} + 2 N H_{4} Cl$

- $C a C O_{3} / M g C O_{3}$ are removed by passing through filter.

ii) Carbonate Tower:

-Ammonical brine is made trickle down from top of carbonation tower and meet with steam of $C O_{2}$ passing from bottom.

$C O_{2} + H_{2} O + N H_{3} \to N H_{4} H C O_{3}$

$N a Cl + N H_{4} H C O_{3} \to N a H C O_{3} + N H_{4} Cl$

- $C O_{2}$ required for carbocation is prepared by heating limestone in lime kiln.

$C a C O_{3} ⟶ △; 10 0^{\circ} C C a O + C O_{2}$

$C a O + H_{2} O \to C a (O H)_{2}$ (used on ammonia recovery tower)

iii) Filtration :

- $N a H C O_{3}$ (Sodium Bicarbonate) is filtrate with the help of vacuum filter.

iv) Ammonia recovery tower :

-Filtrate from vacuum filter containing $N H_{4} Cl$ and little $N a H C O_{3}$ is sent on long tower, ammonia recovery tower. $C a (O H)_{2}$ obtained from lime kiln is also passed on tower.

$N H_{4} H C O_{3} \to N H_{3} + H_{2} O + C O_{2}$

$2 N H_{4} H C O_{3} + C a (O H)_{2} \to 2 N H_{3} + 2 H_{2} O + C a C l_{2}$

-Mixture of $C O_{2}$ and $N H_{3}$ is sent to ammonia absorber for saturation of brine.

v) Calcination of $N a H C O_{3}$ :

- $N a H C O_{3}$ thus obtained is heated strongly.

$2 N a H C O_{3} ⟶ △ N a_{2} C O_{3} + H_{2} O + C O_{2}$

NOTE:

$N a_{2} C O_{3} .10 H_{2} O$ (deca hydrated Na2CO3) = washing soda
$N a_{2} C O_{3}$ = Soda ash
$N a H C O_{3}$ = Baking Soda