Occurrence and Extraction of Metals Questions in English

(B) The ores of iron are minerals from which iron can be extracted profitably. Common iron ores include Hematite $(Fe_2O_3)$ and Magnetite $(Fe_3O_4)$.
- $A$: Cuprite is an ore of copper $(Cu_2O)$.
- $B$: Magnetite is an ore of iron $(Fe_3O_4)$.
- $C$: Malachite is an ore of copper $(Cu_2CO_3(OH)_2)$.
- $D$: Bauxite is an ore of aluminium $(Al_2O_3 \cdot 2H_2O)$.
Therefore, the correct option is $B$.

(C) The process of extracting a metal from its ore and refining it to obtain it in a pure form is known as $Metallurgy$.
$Calcination$ and $Roasting$ are specific chemical processes used during the extraction of metals from ores,while $Smelting$ is a form of extractive metallurgy used to produce a metal from its ore. $Metallurgy$ is the comprehensive term that encompasses all these processes.

(C) The concentration of sulphide ores is typically carried out using the $Froth$ $Floatation$ method.
In this process,the finely powdered ore is mixed with water and pine oil in a tank.
Compressed air is blown through the mixture,creating froth.
Since sulphide ores are preferentially wetted by oil,they stick to the froth and rise to the surface,while the gangue particles (impurities) are wetted by water and settle at the bottom.
The froth containing the concentrated ore is then skimmed off.

(B) The froth flotation process is primarily used for the concentration of sulphide ores.
Copper pyrites $(CuFeS_2)$ is a sulphide ore of copper.
Hematite $(Fe_2O_3)$ is an oxide ore,Cuprite $(Cu_2O)$ is an oxide ore,and Siderite $(FeCO_3)$ is a carbonate ore.
Therefore,Copper pyrites is the correct answer as it is a sulphide ore.

(B) The process of heating carbonate ores in the absence of air or in a limited supply of air to convert them into their respective metal oxides is called $Calcination$.
For example, $ZnCO_3 \xrightarrow{\Delta} ZnO + CO_2$.
In contrast, $Roasting$ involves heating sulfide ores in the presence of excess air.

(B) The process of heating sulphide ores strongly in the presence of excess air is known as $Roasting$.
In this process, the metal sulphide reacts with oxygen to form metal oxide and sulphur dioxide gas.
For example: $2ZnS + 3O_2 \rightarrow 2ZnO + 2SO_2$.
$Calcination$ is used for carbonate ores in limited air, while $Roasting$ is specific to sulphide ores.

(A) The process of removing gangue (impurities like sand,soil,etc.) from the ore is known as concentration of ore or ore dressing.
Common methods for concentration include hydraulic washing,magnetic separation,froth flotation,and leaching.
$A$. Centrifugation is a physical method used for separation based on density,which is often employed in the concentration of ores.
$B$. Calcination is a process of heating ore in the absence of air to remove volatile impurities and moisture.
$C$. Roasting is a process of heating sulfide ores in the presence of excess air.
$D$. Chemical reduction is used to extract metal from the concentrated ore.
Therefore,centrifugation is a method used for the concentration of ore.

(D) The process of removing gangue from an ore is known as concentration or dressing of ore.
Common methods for concentration include Froth flotation,Magnetic separation,and Centrifugation (or Gravity separation).
Calcination is a process used in the extraction of metals from concentrated ore,where the ore is heated strongly in the absence of air to convert carbonates into oxides.
Therefore,Calcination is a metallurgical process used for refining/extraction,not for the concentration of ore.

(D) The froth flotation process is primarily used for the concentration of sulphide ores.
In this process,the ore is finely powdered and mixed with water.
Collectors like pine oil or turpentine are added,which make the sulphide ore particles water-repellent (hydrophobic).
These sulphide particles get wetted by the oil and rise to the surface along with the froth,while the gangue particles (like sand or clay) are wetted by water and settle at the bottom.

(B) The method described involves placing finely powdered ore on a rotating grooved table.
As the table rotates,the heavier ore particles settle in the grooves,while the lighter gangue (impurities) particles are washed away by a stream of water.
This process is known as Gravity Separation or the Wilfley table method,which relies on the difference in densities between the ore and the gangue.
Therefore,the correct option is $B$.

(A) The magnetic separation method is used for the concentration of ores where either the ore or the impurities (gangue) are magnetic in nature.
Iron ores,such as magnetite $(Fe_3O_4)$ or hematite $(Fe_2O_3)$,are magnetic.
In this process,the powdered ore is passed over a conveyor belt moving over magnetic rollers.
The magnetic ore particles are attracted to the magnetic roller and fall closer to it,while the non-magnetic impurities fall further away,allowing for effective separation.
Therefore,iron ore is concentrated using this method.

(A) Roasting is a metallurgical process used for sulphide ores.
In this process, the concentrated sulphide ore is heated strongly in the presence of excess air.
As a result, the sulphide ore is converted into its corresponding metal oxide and sulphur dioxide gas is released.
For example: $2ZnS + 3O_2 \rightarrow 2ZnO + 2SO_2$.

(C) The process of extracting metals from their oxides using aluminium as a reducing agent is known as the thermite reaction or aluminothermic process.
In this process, highly reactive metals like aluminium are used to reduce the oxides of less reactive metals such as chromium $(Cr_2O_3)$ and manganese $(MnO_2)$.
The reaction is highly exothermic, releasing a large amount of heat, which melts the metal produced.
For example: $Cr_2O_3 + 2Al \rightarrow 2Cr + Al_2O_3 + \text{Heat}$.

(D) Aluminum is a highly reactive metal,and its oxide,alumina $(Al_2O_3)$,is very stable.
It cannot be reduced by common reducing agents like carbon or carbon monoxide because the affinity of aluminum for oxygen is much higher than that of carbon.
Therefore,aluminum is extracted from alumina by the process of electrolytic reduction (electrolysis of molten alumina dissolved in cryolite).

(A) Metals that are high in the reactivity series,such as $Al$,$Mg$,$Ca$,$Na$,and $K$,have a higher affinity for oxygen than carbon does.
Therefore,their oxides cannot be reduced by carbon.
Among the given options,$Al$ (Aluminium) is the most reactive metal and its oxide $(Al_2O_3)$ cannot be reduced by carbon.
Other metals like $Fe$,$Zn$,and $Pb$ are less reactive and their oxides can be reduced by carbon.

(C) The most common and effective method for the refining of copper metal is $Electrolytic$ $refining$.
In this process, an impure copper block is used as the anode, and a thin strip of pure copper is used as the cathode.
An aqueous solution of copper sulfate $(CuSO_4)$ mixed with dilute sulfuric acid $(H_2SO_4)$ is used as the electrolyte.
When an electric current is passed through the solution, pure copper from the anode dissolves into the electrolyte and deposits onto the cathode, while impurities settle at the bottom of the anode as 'anode mud'.

(D) Refining is the process of purifying an impure metal. Common methods of refining include Liquation,Electrolytic refining,and Zone refining.
Calcination is a process used in the extraction of metals,specifically for converting carbonate ores into oxides by heating them in a limited supply of air. It is a step in the extraction process,not a method of refining.

(B) In the electrolytic refining of copper,an electrolytic cell is set up using an aqueous solution of copper sulfate $(CuSO_4)$ acidified with sulfuric acid as the electrolyte.
An impure block of copper is used as the anode,while a thin strip of pure copper is used as the cathode.
When an electric current is passed through the electrolyte,pure copper from the anode dissolves into the solution,and an equivalent amount of pure copper from the electrolyte gets deposited on the cathode.
Therefore,a pure copper rod is used as the cathode.

(A) In the electrolytic refining of copper,an impure copper rod is used as the anode and a thin strip of pure copper is used as the cathode.
When an electric current is passed through the electrolyte (acidified copper sulfate solution),copper ions $(Cu^{2+})$ from the solution move towards the cathode.
At the cathode,these $Cu^{2+}$ ions gain two electrons and get reduced to form pure copper metal,which deposits on the cathode.
Therefore,pure copper deposits at the cathode.

(C) In the electrolytic refining of copper,an impure copper rod is used as the anode and a thin strip of pure copper is used as the cathode.
When an electric current is passed through the electrolyte (acidified copper sulfate solution),the impure copper from the anode dissolves into the solution as $Cu^{2+}$ ions.
These $Cu^{2+}$ ions then migrate to the cathode,where they gain electrons and deposit as pure copper metal.
As the impure copper anode continuously loses copper atoms to the solution,its weight decreases over time.
Conversely,the weight of the pure copper cathode increases as more copper is deposited on it.

(C) Liquation is a metallurgical process used for the purification of metals that have a low melting point compared to their impurities.
In this process,the crude metal is placed on the sloping hearth of a furnace and heated.
The metal melts and flows down the slope,leaving behind the non-fusible impurities.
Tin $(Sn)$ is a classic example of a metal purified by this method because it has a relatively low melting point $(231.9 \ ^\circ C)$ compared to the impurities associated with it.

(B) Liquation is a metallurgical process used for the purification of metals that have low melting points,such as tin $(Sn)$,lead $(Pb)$,and bismuth $(Bi)$.
In this process,the impure metal is placed on the sloping hearth of a reverberatory furnace and heated gently.
The metal melts and flows down the slope,leaving behind the infusible impurities on the hearth.
Thus,the correct option is $B$.

(A) Fractional distillation is a process used for the separation of a mixture into its components or fractions.
It works on the principle of the difference in the boiling points of the components present in the mixture.
When the mixture is heated,the component with the lower boiling point vaporizes first,followed by the component with the higher boiling point.
This method is commonly used to separate components of crude oil or to separate gases from the air.

(B) In the process of electrolytic refining, an impure metal rod is used as the anode and a thin strip of pure metal is used as the cathode.
When an electric current is passed through the electrolyte, the pure metal from the anode dissolves into the electrolyte, and an equivalent amount of pure metal from the electrolyte deposits on the cathode.
The insoluble impurities present in the impure metal, which do not dissolve in the electrolyte, settle down at the bottom of the electrolytic cell below the anode.
This collection of insoluble impurities is known as $Anode \text{ } mud$.

(C) Zone refining is a method used to purify semiconductors like $Si$,$Ge$,and $Ga$.
This process is based on the principle that impurities are more soluble in the molten state of the metal than in the solid state.
$A$ circular mobile heater is fixed at one end of a rod of the impure metal.
As the heater moves,the pure metal crystallizes out of the melt,and the impurities pass into the adjacent molten zone.
This process is repeated several times until the impurities are concentrated at one end,which is then cut off.

(A) The process of extracting pure alumina $(Al_2O_3)$ from bauxite ore is known as the Bayer's process.
In this process,bauxite is treated with a concentrated solution of sodium hydroxide $(NaOH)$ at high pressure and temperature.
This dissolves the alumina to form sodium aluminate,while impurities like silica,iron oxide,and titanium oxide remain as insoluble residues (red mud).
The solution is then filtered,and the pure alumina is precipitated out.

(C) The Bayer process is the principal industrial means of refining bauxite to produce alumina $(Al_2O_3)$.
In this process,bauxite ore is treated with a hot concentrated solution of sodium hydroxide $(NaOH)$.
The concentration of the sodium hydroxide solution used is typically around $45\%$ by weight.
This treatment dissolves the aluminum-bearing minerals to form sodium aluminate,while impurities like iron oxide remain as a solid residue (red mud).

(B) The $Bayer$ process is the principal industrial means of refining bauxite to produce alumina $(Al_2O_3)$.
In this process,finely ground bauxite ore is digested with a hot concentrated solution of $NaOH$ under pressure.
The $Al_2O_3$ present in the bauxite reacts with $NaOH$ to form soluble sodium aluminate ($NaAlO_2$ or $Na[Al(OH)_4]$).
The chemical reaction is: $Al_2O_3(s) + 2NaOH(aq) + 3H_2O(l) \rightarrow 2Na[Al(OH)_4](aq)$.

(A) Bayer's process is used for the purification of bauxite ore to obtain pure alumina $(Al_2O_3)$.
In this process,the bauxite ore is treated with a concentrated solution of sodium hydroxide $(NaOH)$ at high temperature and pressure.
The impurities like silica,iron oxide,and titanium oxide are removed during the process.
The final alumina obtained after calcination is highly pure,typically containing about $99.5\%$ pure $Al_2O_3$.
Therefore,the impurity remaining in the alumina is approximately $100\% - 99.5\% = 0.5\%$.

(B) The extraction of aluminium from pure alumina $(Al_2O_3)$ is carried out by the electrolytic reduction process known as the Hall-Heroult process.
In this process,pure alumina is dissolved in molten cryolite $(Na_3AlF_6)$,which lowers the melting point of the mixture and increases its electrical conductivity.
Electrolysis is then performed in a steel tank lined with carbon,where aluminium is deposited at the cathode.

(D) Cryolite is a rare mineral with the chemical composition $Na_{3}AlF_{6}$.
It is chemically known as sodium hexafluoroaluminate.
It is primarily used in the electrolytic process of extracting aluminium from alumina $(Al_{2}O_{3})$ to lower the melting point of the mixture and increase its electrical conductivity.

(B) In the $Hall-Heroult$ process,pure alumina $(Al_2O_3)$ has a very high melting point and is a poor conductor of electricity.
To overcome these issues,cryolite $(Na_3AlF_6)$ and fluorspar $(CaF_2)$ are added to the alumina.
These substances lower the melting point of the mixture to approximately $1240 \ K$ and increase its electrical conductivity,facilitating the electrolytic reduction of aluminum.

(C) The most abundant metal in the Earth's crust is $Aluminium$ $(Al)$,which accounts for approximately $8.1\%$ of the crust by weight.
The second most abundant metal in the Earth's crust is $Iron$ $(Fe)$,which accounts for approximately $5.0\%$ of the crust by weight.
Therefore,$Iron$ is the second most abundant metal found on Earth.

(A) The extraction of iron from its ore (mainly hematite, $Fe_2O_3$) is carried out in a $Blast$ furnace.
In this process, iron ore, coke, and limestone are fed into the top of the furnace, while hot air is blasted into the bottom.
The coke acts as a fuel and a reducing agent, converting iron oxides into molten iron.

(B) In a blast furnace, the primary ore used for the extraction of iron is $Hematite$ $(Fe_2O_3)$.
During the process, the ore is reduced by carbon monoxide $(CO)$ at high temperatures to produce molten iron.
The chemical reaction is: $Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2$.

(A) In the blast furnace,limestone $(CaCO_3)$ is added as a flux. It decomposes to form calcium oxide $(CaO)$.
$CaCO_3 \rightarrow CaO + CO_2$
The calcium oxide $(CaO)$ reacts with the silica $(SiO_2)$ impurity present in the ore to form molten calcium silicate $(CaSiO_3)$,which is known as slag.
$CaO + SiO_2 \rightarrow CaSiO_3$ (Slag)
Therefore,the correct answer is calcium silicate.

(C) In the blast furnace,iron oxides are reduced by carbon monoxide $(CO)$ at different temperature zones.
$1$. At lower temperatures $(500-800 \ K)$: $3Fe_{2}O_{3} + CO \longrightarrow 2Fe_{3}O_{4} + CO_{2}$ and $Fe_{3}O_{4} + CO \longrightarrow 3FeO + CO_{2}$.
$2$. At higher temperatures $(> 1000 \ K)$: $FeO + CO \longrightarrow Fe + CO_{2}$.
Option $C$ is incorrect because $Fe_{3}O_{4}$ is being reduced to $Fe_{2}O_{3}$ (an oxidation process) and it produces solid carbon,which does not occur in this reduction sequence.

(C) Haematite is one of the most important ores of iron.
Its chemical formula is $Fe_{2}O_{3}$.
- $Fe_{3}O_{4}$ is the formula for Magnetite.
- $FeCO_{3}$ is the formula for Siderite.
- $FeS_{2}$ is the formula for Iron Pyrites (Fool's Gold).
Therefore,the correct option is $C$.

(D) In a blast furnace,$Coke$ $(C)$ acts as a reducing agent. It reacts with oxygen to form carbon monoxide $(CO)$,which then reduces iron oxides to molten iron. Furthermore,the presence of $Coke$ and the reducing atmosphere created by $CO$ prevents the re-oxidation of the molten iron produced.

(A) In the extraction of iron from its ore,limestone $(CaCO_{3})$ is added as a flux.
At high temperatures,limestone decomposes to form calcium oxide $(CaO)$ and carbon dioxide $(CO_{2})$.
The calcium oxide $(CaO)$ reacts with the silica $(SiO_{2})$ impurity present in the ore to form calcium silicate $(CaSiO_{3})$,which is known as slag.
The chemical reaction is: $CaO + SiO_{2} \rightarrow CaSiO_{3}$ (slag).
Therefore,the correct molecular formula for calcium silicate is $CaSiO_{3}$.

(D) Let us evaluate each group:
$(1)$ Iron - Magnetite - $Fe_{3}O_{4}$: This is correct. Magnetite is an oxide ore of iron with the formula $Fe_{3}O_{4}$.
$(2)$ Iron - Siderite - $FeS_{2}$: This is incorrect. Siderite is $FeCO_{3}$. $FeS_{2}$ is Iron Pyrites.
$(3)$ Copper - Copper glance - $Cu_{2}S$: This is correct. Copper glance (Chalcocite) is a sulfide ore of copper with the formula $Cu_{2}S$.
$(4)$ Copper - Dolomite - $Al_{2}O_{3}$: This is incorrect. Dolomite is $CaCO_{3} \cdot MgCO_{3}$. $Al_{2}O_{3}$ is Corundum (an ore of Aluminum).
Therefore, only groups $(1)$ and $(3)$ are correct.

(B) The correct pairings are as follows:
$1$. Extraction of sulphur is done by the $Frasch$ method $(1-q)$.
$2$. Production of nitric acid is done by $Ostwald's$ method $(2-s)$.
$3$. Production of sulphuric acid is done by the $Contact$ process $(3-p)$.
$4$. Production of ammonia gas is done by $Haber's$ process $(4-r)$.
Therefore,the correct sequence is $(1-q), (2-s), (3-p), (4-r)$.

(A) The mineral of sulfur among the given options is Galena $(PbS)$.
Galena is the primary ore of lead and is chemically known as lead sulfide.
Silica is silicon dioxide $(SiO_2)$.
Horn silver is silver chloride $(AgCl)$.
Siderite is iron carbonate $(FeCO_3)$.

(C) Sulphur is extracted from underground deposits in the earth's crust using the $Frasch$ process.
In this method,superheated water $(170 \ ^\circ C)$ is pumped into the sulphur deposit to melt it.
The molten sulphur is then forced to the surface by compressed air.
$Contact$ process is used for the manufacture of sulphuric acid.
$Haber's$ process is used for the production of ammonia.
$Oswald's$ process is used for the production of nitric acid.