Refining of metals - class-X

Smelting is process in which metal is extracted from its ore by heating and melting. It is not a method of refining metal. Methods of refining metals are electrolysis poling, liquation, zone refining, vapour phase refining, distillation.

$Ni$ is refined by Mond's process.

Low boiling point metals like Mercury are purified with distillation.

Electrolysis, process by which electric current is passed through a substance to effect a chemical change. The chemical change is one in which the substance loses or gains an electron (oxidation or reduction).

The removal of  metallic impurities from lead is known as 'Softening of lead'.

The purest copper is obtained by an electrolytic process using impure copper as the anode and a thin sheet of pure copper as cathode. The electrolyte is an acidic solution of copper sulphate. By passing electricity copper is dissolved from anode and deposits at cathode.

Both Sodium and calcium are highly reactive metal oxides are not reduced by carbon and these metals are obtained in free state by electrolytic reduction of their molten chloride salts.

In electrolytic refining, impure metal is made the anode and a thin strip of pure metal is made the cathode.

Refining of metals is required because the metals that have been extracted by concentration of ore are still impure.

Separation of impurities from the extracted metals is known as refining of metals.

In the electrolytic refining the process the impure sample is used as anode and pure metal is obtained at cathode. Impurities present at anode are deposited at the bottom and called as anode mud.

Refining of aluminium is done by electrolytic method. The aluminium obtained is 99.99% pure.

Roasting is the method of converting the ore to its oxide form . It is not a method of refining.

Electrolysis is the dissolving of metal from one electrode of an electrolytic cell to another electrode in pure form. It gives the highest purity metal product. The impure silver is cast into a slab which is the anode, while pure silver sheet metal is the cathode.

Sodium is obtained by the electrolysis of fused mixture of $NaCl$ and $CaCl _2$ (Down's process). Reaction can be written as:

After extraction and separation, refining is the last process of Metallurgy. It involves the refining of pure metal finally. 

Copper and Silver are often refined using electrolytic refining, where an impure metal anode is dissolved and pure metal is deposited at the cathode. Silicon and Germanium are typically refined using zone refining.

In electrorefining step, impurities like Fe, Ni, Zn get dissolved in the solution while Au, Ag and Pt are deposited as anode mud below the anode and pure copper deposited at cathode.

The Van Arkel method is a specific technique used for the refining of zirconium and titanium. It involves the formation of a volatile iodide compound which is then thermally decomposed to obtain pure metal.

Anode mud is the insoluble impurity which settles down at the bottom of the anode during electrolytic refining. The soluble impurities go into the solution.

Poling is a method employed in the purification of copper which contains cuprous oxide as an impurity. Silver containing lead as an impurity is not purified by polling.

Sodium and calcium are the metals obtained by electrolysis of their chlorides in molten state. Both are reactive metals.

In the electrolytic refining of zinc

Anode → impure zinc

Cathode → strip of pure zinc

Electrolyte → acidified zinc sulphate solution

At anode → Oxidation of metal

                     (i.e., $Zn \longrightarrow Zn^{2+} + 2e^–$)

                            (impure)

At cathode → reduction of metal ions

                       (i.e., $Zn^{2+} + 2e^– \longrightarrow Zn$)

                          (Form solution)    (pure)

Aluminium is purified by electrolytic reduction. Aluminium lies on the top of electrochemical series therefore it is purified by electrolytic refining.

Metals such as Cu, Ag, Zn, Sn, Pb, Al, Ni, Cr are refined by electrolytic refining method. The impure metal is made the anode of a electrolytic cell, while cathode is thin plate of pure metal. Electrolyte is the solution of a double salt of the metal. On passing the electric current pure metal from the anode dissolves and gets deposited at the cathode. The soluble impurities go into the solution while insoluble or less electropositive impurities settle down below the anode as anode mud or sludge. 

The impure copper from a smelter is cast into a block to form the positive anode and the cathode is made up of purified copper. These are dipped into an electrolyte of copper sulphate solution. purification of aluminium can be carried out by the Hoopes process. This is an electrolytic process.

The sodium and chloride produced in the electrolysis are kept from coming in contact with each other as the sodium is highly reactive and it must be prevented from coming in contact with oxygen as the metal quickly oxidizes under high temperature conditions.

Copper and zinc will be refined in electrolytic refining process for the following reasons.

On passing the current through the electrolyte, pure metal from the anode dissolves into the electrolyte. An equivalent amount of pure metal from electrolyte is deposited on the cathode.

A solution of the metal salt is used as an electrolyte. Impute metal is made the anode and a thin strip of pure metal is made of cathode.

Separation of impurities from the extracted metals is generally done by electrolysis of impure metals.

Lead is refined by electrolytic method. The other metals which are also refined by this method are aluminium and copper.

Sodium metal is refined by electrolytic method. 

Iron obtained after extraction by reduction contains 3−4% carbon and other impurities like phosphorus, manganese etc. This is called as pig iron.

By heating pig iron in furnace it is converted to wrought iron. It is the pure form of iron which contains carbon. It is soft, grey, tough, malleable and ductile.

Refining consists of purifying an impure material, in this case, a metal. It is to be distinguished from other processes such as smelting and calcining in that those two involve a chemical change to the raw material, whereas in refining, the final material is usually identical chemically to the original one, only it is purer.

The purest copper is obtained by an electrolytic process, undertaken using a slab of impure copper as the anode and a thin sheet of pure copper as the cathode. The electrolyte is an acidic solution of copper sulphate. 

The purest copper is obtained by an electrolytic process, undertaken using a slab of impure copper as the anode and a thin sheet of pure copper as the cathode.

Definition of electrolytic reduction: Removal of oxygen (or decrease of its active valency in the case of a positive element) by electrical means.

Nickel metal is purified by the vapour phase refining process. This process is based on the fact that nickel reacts with carbon monoxide to form highly volatile nickel tetracarbonyl which decomposes at high temperature to form pure nickel metal.
 $\displaystyle Ni+4CO \xrightarrow {\text {330-350 K}} Ni(CO) _4$
 $\displaystyle Ni(CO) _4 \xrightarrow { \text {450-470 K}}  \underset {\text {Pure metal }}{Ni}+ 4 CO$

Because of their electronegativity of the chlorine atom in their ores, the electronic influence is more. So, they are extracted by electrolytic reduction. 

Both calcination and roasting are generally carried out in the this furnace, one in absence of air and other in presence of air.
The slag formed during the extraction of Copper metal from Chalcopyrites ore is $FeSiO _3$.
Mond's process involved in the extraction of Nickel is related with formation and decomposition of a tetrahedral complex of nickel metal $[Ni(CO) _4]$. 

Cupellation is a process where ores are treated under high temperatures and controlled operations to separate noble metals like gold and silver from base metals like lead, copper, zinc, and others present in the ore or alloyed metal.

Cupellation is a process where ores are treated under high temperatures and controlled operations to separate noble metals like gold and silver, from base metals like led, copper, zinc, and others present in the ore or alloyed metal.

Cupellation is a process where ores are treated under high temperatures and controlled operations to separate noble metals like gold and silver, from base metals like led, copper, zinc, and others present in the ore or alloyed metal.

Cupellation is a process where ores are treated under high temperatures and controlled operations to separate noble metals like gold and silver, from base metals like led, copper, zinc, and others present in the ore or alloyed metal.

When alloy of silver and lead is rich in silver, cupellation process is used.
The silver metal can be obtained in when alloy of silver and lead is rich in lead is:
i) Parke's process
ii) Pattinson's process

We know the melting point of pure lead is very high. Softening of lead means removal of metallic impurities, except silver, present in the commercial lead. 

Tin is obtained by reducing the ore cassiterite with coal in a reverberatory furnace; limestone is added to produce a slag with impurities, which can be removed.

$SnO _2  +  2C \longrightarrow Sn + 2 CO$.

Crude tin so obtained is contaminated with iron, lead, and other metals. It is, therefore, remelted on an inclined furnace. The process is called liquation. The easily fusible tin metals away and the less fusible impurities are left behind. Molten tin is finally stirred with green poles of wood in contact with air. In this process, any remaining metal impurities are oxidized forming a scum, which rises to the surface and is removed. This process is called polling.

A) Poling is a method employed in the purification of copper which contains cuprous oxide as an impurity.correct.
B) Cupellation is a refining process in metallurgy, where ores or alloyed metals are treated under high temperatures and controlled operations to separate gold and silver, from lead, copper, zinc, arsenic, antimony or bismuth.correct.
C) The process of extracting a metal from its oxide is known as 'smelting'. Most smelting processes involve direct reduction of the ore by carbon to metal and carbon dioxide. The production of primary aluminium is a good example of such a process. Its not oxidation.wrong
D) Roasting is a step of the processing of certain ores More specifically, roasting is a metallurgical process involving gassolid reactions at elevated temperatures with the goal of purifying the metal component(s). During roasting, the sulfide is converted to an oxide, and sulfur is released as sulfurdioxide, a gas.$2Cu _2S + 3O _2\rightarrow  2 Cu _2O + 2 SO _2$.correct.
options A,B & D are correct.

Poling is a process in which the impure metal containing oxide as impurities is purified. It is melted and stirred with green poles of wood. Hydrocarbon gases escaping from the poles act as reducing agents and reduce the oxide impurities e.g., impurity of Cu$ _2$O which is reduced to metallic copper by poling.
$Cu _2O + CO \rightarrow 2Cu + CO _2 \uparrow$
$Cu _2O + H _2 \rightarrow 2Cu + H _2O$

True. Polling is used for converting Copper Oxide $(Cu _2O)$ to Copper $(Cu)$. When ore is heated with wood poles, the poles release charcoal, shoot and gas. The gas released reduces $CuO$ to $Cu$. So the gas takes away impurities. 

Cupellation is a process of separation of gold or silver from impurities by melting the impure metal in a cupel (a flat porous dish made of refractory or high-temperature resistant material  ) and then directing a blast of hot air on it in a special furnace. The impurities, including lead,copper, tin, and other unwanted metals, are oxidized and partly vaporized and partly absorbed into the pores of the cupel.

Poling: A refining process of crude metal for removing metal oxide impurities by stirring molten metal in a ladle with a pole of green wood (poles).