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Physical Chemistry

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Physical Chemistry-II

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Inorganic Chemistry

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

Zinc

Introduction:

Atomic Number: $30$
Electronic Configuration: $[A r] 3 d^{10} 4 s^{2}$
Symbol: $Z n$
Zinc is present in the d-block of the Periodic Table, it does not behave like other transition elements. This abnormality is due to the filled d-orbitals.
It has specific gravity of $7.17$
Ores:

-Zinc blend: $Z n S$ (Main Ore)

-Zincite: $Z n O$

-Calamine: $Z n C O_{3}$

Oxidation State: $+ 2$
Forms colourless compound.

Extraction of Zinc using Zinc Blend:

-It can be extracted by two different methods:

i) Carbon reduction process

ii) Electrolyte process

-We discuss Carbon Reduction Process only.

Carbon Reduction Process:

Crushing and Pulverization:

-Ore is crushed by jaw crusher and pulverized( powder) using ball mills.

Concentration:

-As zinc blend $(Z n S)$ is sulphide ore, it is concentrated by froth floatation.

-Pine oil or Eucalyptus oil acts as the frothing agent.

-The sulphide ore is deposited on surface as froth.

Calcination or Roasting:

-Since, it is sulphide ore, the ore is roasted i.e. heated at excess supply of air.

$2 Z n S + 3 O_{2} ⟶ ∆ 2 Z n O + 2 S O_{2}$

-During heating, some $Z n S$ are also converted to $Z n S O_{4}$ .

$Z n S + 3 O_{2} ⟶ △ Z n S O_{4}$

-If Calamine ore was there calcination was done:

$Z n C O_{3} (C a l c ina t i o n) \to Z n O + C O_{2} ↑$

Above, $90 0^{\circ} C$

$Z n S O_{4} \to 2 Z n O + 2 S O_{2} + O_{2}$

During roasting, volatile impurities are removed as oxide.

$S + O_{2} ⟶ ∆ S O_{2} ↑$

$C + O_{2} ⟶ ∆ C O_{2} ↑$

Reduction:

-Roasted $Z n O$ is heated with carbon in furnace to reduce oxide to metallic form.

$Z n O + C + ⟶ ∆ Z n + CO$

Different reduction process are employed. They are:

a) Vertical Retort Process

b) Belgian Process

c) Silesian Process

-As vertical retort process is economical and modern process, it is used.

Continuous Vertical Retort Process:

-In this process ZnO and Coke in $2 : 1$ ratio is taken and heated by burning Producer Gas $(CO + N_{2})$ at about $140 0^{\circ} C$ .

-In this condition, Zinc oxide is reduced to zinc which vaporizes.

-The vapor of Zinc and $CO$ after reduction is passed through condenser after release of volatile impurities called Spelter Zinc.

-The fresh charge is added continuously from charging door and residual waste material is taken out from bottom.

Purification:

-Impurities like Pb, Fe, Cd, etc are present which can be purified by:

a) Liquation:

-Zinc metal is melted on the sloping hearth of reverberatory furnance.

-Molten zinc flows down leaving non-fusible impurities.

b) Fractional Distillation:

-Distillation at $10 0^{\circ} C$ separates $Z n an d C d$ having low boiling point than $P b, F e,$ etc. having higher bpt and distillation at $80 0^{\circ} C$ separates $C d$ $(b pt . 76 7^{\circ} C)$ from zinc $(b pt .90 7^{\circ} C)$ .

c) Electrolytic Refining:

Anode= impure zinc (spelter zinc)
Cathode=pure zinc
Electrolyte of $Z n S O_{4}$ Solution.
Pure zinc is deposited at cathode and impurities are left in bottom as anode mud.

Note:

$Z n O$ is known as philosopher's wool.
$Z n S O_{4} .7 H_{2} O$ is known as White Vitriol.
$Z n C l_{2}$ is called butter of Zinc

Chemical Properties:

Oxidation of air:

$2 Z n + O_{2} + H_{2} O + C O_{2} \to Z n C O_{3} . Z n (O H)_{2}$

But,

$Z n + O_{2} + \to ∆ Z n O$

With Water:

$Z n + H_{2} O \to Z n O + H_{2}$

With Acid:

-Displace $H_{2}$ from non-oxidizing acid.

$Z n + H Cl \to Z n C l_{2} + H_{2}$

$Z n + d i l . H_{2} S O_{4} \to Z n S O_{4} + H_{2}$

$Z n + 2 co n c . H_{2} S O_{4} \to Z n S O_{4} + S O_{2} + 2 H_{2} O$

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

$3 Z n + 8 m o d . co n c . H N O_{3} \to 3 Z n (N O_{3})_{2} + 2 NO + 4 H_{2} O$

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

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

With Alkali:

$Z n + 2 N a O H \to N a_{2} Z n O_{2} + H_{2}$

$Z n + 2 K O H \to K_{2} Z n O_{2} + H_{2}$

Displacement:

$Z n + C u S O_{4} \to C u ↓ + Z n S O_{4}$

$Z n + A g N O_{3} \to A g ↓ + Z n (N O_{3})_{2}$

$Z n + N i S O_{4} \to N i ↓ + Z n S O_{4}$

With Non-Metal:

$Z n + C l_{2} \to ∆ Z n C l_{2}$

$2 Z n + O_{2} \to ∆ 2 Z n O$

$Z n + S \to ∆ Z n S$

Uses

To galvanic iron
To make electrodes.
To make alloys such as brass, german silver, electron, etc.

Galvanization:

-Process of coating zinc over the surface of iron in order to protect it from rusting.

-It is done by following process:

1) Cleaning of the article:- By sand blasting and dipped on dil. HCl or H2SO4 to remove any oxide film and rinsed with water.

2) Galvanization:

i) Ordinary Galvanization:

-Process in which iron steel is dipped into molten zinc for coating.

ii) Heated Galvanization:

-Process in which iron sheet is dipped into molten zinc for coating.

iii) Electro-galvanization:

-It is the method in which electroplating is performed for galvanization.

-Cathode: Iron

-Anode: Zinc

-Electrolyte: $Z n S O_{4}$

Note:

-Zinc obtained by dropping molten zinc in cold water is called granulated zinc.