General Principles And Processes Of Isolation

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General Principles And Processes Of Isolation – General Principles And Processes Of Isolation is ncert notes for class 12th..

Minerals

Minerals are naturally occurring chemical substances in the earth’s crust obtained by mining.

Ores

The minerals from which we can obtain metal chiefly, profitably and easily are known as ores.

Principal ores of some important metals are-

General Principles And Processes Of Isolation

Gangue

The undesired materials present in the ore are known as gangue.

Metallurgy

The process of extracting pure form of a metal from their ores is called metallurgy.

Flux– The substance which is added in the ore to convert non-fusible gangue to fusible compound is called flux. There maybe acidic flux and basic flux.

Slag– The fusible compound formed by the combination of flux and gangue is called slag.

Crushing of Ores– Big lumps of ore are first broken into small pieces by crushers and then with the help of grinder, it changes into powder form.

Concentration of Ores – Concentration, benefaction or dressing is the removal of the unwanted materials from the ore. It involves several steps such as hydraulic washing, magnetic separation, froth floatation method and leaching.

Hydraulic Washing Method – This method is based on the difference between density of the ore particles and particles of impurities(gangue).

Magnetic Separation Method– Magnetic separation is based on the difference in the magnetic properties of the ore and the impurities. It is used if either the ore or the gangue is magnetic.

Froth Floatation Method– This method is based on the wetting preference of ore and gangue particles with water and oil. Generally sulphide ores are concentrated by this method.

Calcination– The process of heating metal ore on the absence of air is called calcination.

Roasting– The process of heating metal ore below its melting point in the presence of air is called roasting.

NOTE* In calcination and roasting, ore is converted to oxide.

Pyrometallurgy– The process of extraction of a metal by heating the metal oxide with a suitable reducing agent is known as pyrometallurgy.

Hydrometallurgy– The process of extraction of metal by dissolving the ore in a suitable reagent followed by precipitation or displacement of the metal by a more electropositive metal is known as hydrometallurgy.

Smelting– Mixing of ore with coke and different flux and fusion at high temperature is known as smelting.

Electrolytic Process– By this method Cu, Al, Ag metals are extracted.

Self-reduction– By this method copper, lead and mercury are extracted from there sulphides. e.g. Extraction of copper metal

{2Cu}_{2} {S} + {3O}_{2}\longrightarrow {2Cu}_{2} {O} + {2SO}_{2}

{2Cu}_{2} {O} + {Cu}_{2} {S} \xrightarrow{Self  - reduction} {6Cu} + {SO}_{2}

Thermodynamic Principles of Metallurgy– The reduction of metal should be thermodynamically feasible. For the change in Gibbs free energy,  \Delta {(G)} must be negative. It is describe by the relation: \Delta {(G°)} = \Delta{H} - {T} \Delta {S}

Where, \Delta{H} = enthalpy change and \Delta {S} is entropy change. This change can also written as \Delta {G°} = -RT  ln  K

where, K is equilibrium constant. If reactants and products of two reactions put together in a system to give overall value of \Delta {G} = negative, the reaction is feasible.

Coupling of Reaction– If the value of \Delta {G} is positive for any reaction, then to make such reaction spontaneous, it is coupled with another reaction of large -ve \Delta {G} value so that the sum of two \Delta {G}   becomes -ve. This is known as coupling of reaction.

Ellingham diagram– Ellingjam diagram is the graphical representation of Gibbs energy change {vs} absolute temperature for a process.

Cast iron– Cast iron is made by melting pig iron with scrap iron and coke using hot air blast. It contains 3% of carbon, It is extremely hard and brittle.

Wrought Iron– This iron is the purest form of commercial iron.

Gibbs Energy– The concept of electrode potential is useful in the isolation of metals where the sum of the two redox couples is positive so that the gibbs energy change is negative.

Distillation– Distillation is very useful for low boiling metals such as Hg and Zn. The mixed metal is evaporated to obtain the pure metal as distillate.

Liquification– Liquification used for low melting metals like tin, which can flow on sloping surface.

Polling– In this method molten metal is stirred with green wooden poles at high temperature. At this high temperature, green wood liberates hydrocarbon gases like methane (CH4), which reduces oxides present in the metal.

Electro – refining – Most of the metals are purified by this method. In this method, the impure metal is turns into a block which forms the anode while cathode is a rod or plate of pure metal. These electrodes are hang up in an electrolyte which is the solution of a soluble salt of the metal. When electric current is passed, metal ions form the electrolyte are deposited at the cathode in the form of pure metal. The soluble impurities present in the crude metal, go into the solution while insoluble impurities settle down below the anode as anode mud or anode sludge.

Vapour phase refining – when metal can be converted to its volatile compound and is collected elsewhere; which on decomposition gives pure metal. This method is known as vapour phase refining. Example mond’s process.

Zone refining- Zone refining is used to obtain metals of high purity. It is based on the principle that the impurities are more soluble in molten state than in the solid state of metal.

Chromatographic method– Chromatographic method is based on the principle that different components of a mixture are differently observed on an adsorbent. The absorbed components are removed by using suitable solvent called eluants. This method is very useful for purification of the elements which are available in minute quantities and the impurities are not very different in chemical properties from element to be purified.

Park’s method– This method is used to purify silver.

Uses of aluminium

  • In making coins used to wrap items like chocolates and cigarettes.
  • In Paint industry.
  • In extraction of chromium and magnesium from their oxides

Uses of copper-

  • In making electric wires.
  • In making a steam types of water.
  • In making several alloys.

Uses of iron

  • Cast iron is used for Casting stoves etc.
  • In making Railway sleepers, gutter pipes etc.
  • In making wrought iron and steel.
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