Reduction to free Metal Questions in English

(C) In the extraction of copper,the copper sulfide $(Cu_2S)$ is partially roasted to form copper oxide $(Cu_2O)$.
$2Cu_2S + 3O_2 \rightarrow 2Cu_2O + 2SO_2$
The remaining copper sulfide then reacts with the copper oxide to produce metallic copper,a process known as self-reduction.
$2Cu_2O + Cu_2S \rightarrow 6Cu + SO_2$

(A) flux is a substance added to the furnace to remove gangue (impurities) from the ore.
Acidic flux is used to remove basic impurities.
$SiO_2$ (silica) is an acidic oxide and acts as an acidic flux.
It reacts with basic impurities like $CaO$ to form slag: $CaO + SiO_2 \rightarrow CaSiO_3$ (slag).
Therefore,$SiO_2$ is the correct answer.

(C) Metals with high electropositive character are extracted by electrolytic reduction. $Al_2O_3$ is reduced to $Al$ using the Hall-Heroult process,which is an electrolytic reduction method.

(D) In the extraction of $Fe$ (iron),the impurity present is $SiO_2$ (silica),which is acidic in nature. To remove this,$CaO$ (calcium oxide) is added as a flux. The reaction is: $CaO + SiO_2 \rightarrow CaSiO_3$. Here,$CaSiO_3$ (calcium silicate) is the slag formed.

(C) In the blast furnace,the iron ore is reduced to iron. The impurities present in the ore,such as silica $(SiO_2)$,are removed by adding limestone $(CaCO_3)$ as a flux.
$CaCO_3$ decomposes to form $CaO$ and $CO_2$.
$CaCO_3 \rightarrow CaO + CO_2$
$CaO$ then reacts with the silica impurity $(SiO_2)$ to form calcium silicate $(CaSiO_3)$,which is the slag.
$CaO + SiO_2 \rightarrow CaSiO_3$ (Slag)
Therefore,the slag produced is primarily $CaSiO_3$ along with other silicate impurities like aluminium silicate if alumina is present in the ore.

(A) The reduction of metal sulphides to metal is thermodynamically unfavourable because the formation of $CS_2$ is not spontaneous compared to the formation of $CO_2$ when carbon is used as a reducing agent.
Since $CO_2$ is thermodynamically much more stable than $CS_2$,the conversion of metal sulphides to oxides makes the subsequent reduction with carbon thermodynamically feasible.

(B) The process of heating an ore with carbon in the absence of air to extract the metal is known as $Smelting$.
In this process,carbon acts as a reducing agent to reduce the metal oxide to its metallic form.

(B) $Pb$ is extracted from galena $(PbS)$ primarily by self-reduction (roasting followed by reaction with remaining sulfide).
$2PbO + PbS \rightarrow 3Pb + SO_2$
$PbSO_4 + PbS \rightarrow 2Pb + 2SO_2$
$Sn$ is extracted from cassiterite $(SnO_2)$ by reduction with carbon $(C)$:
$SnO_2 + 2C \rightarrow Sn + 2CO$

(C) The extraction of gold $(Au)$ and silver $(Ag)$ from their native ores involves leaching with a dilute solution of $NaCN$ or $KCN$ in the presence of air $(O_2)$,which provides the necessary oxygen to oxidize the metal.
The chemical reaction for gold is:
$4Au(s) + 8CN^-(aq) + 2H_2O(aq) + O_2(g) \rightarrow 4[Au(CN)_2]^-(aq) + 4OH^-(aq)$
This process is known as the MacArthur-Forrest cyanide process.

(A) In a blast furnace,$C$ (coke) is used as a fuel as well as a reducing agent. $C$ reacts with $O_2$ to produce $CO_2$ and heat,and further reacts with $CO_2$ to form $CO$,which acts as the primary reducing agent for metal oxides.

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

(A) In metallurgy,a flux is a chemical substance added to the ore during smelting to remove gangue (impurities).
It reacts with infusible impurities (like $SiO_2$) to form a fusible substance known as slag (e.g.,$CaSiO_3$).
Therefore,the flux converts infusible impurities into a fusible form.

(B) The extraction of $Ag$ from argentite $(Ag_2S)$ involves the following steps:
$1$. Leaching: $Ag_2S + 4NaCN + \frac{1}{2}O_2 \rightarrow 2Na[Ag(CN)_2] + Na_2S$. Here,$O_2$ acts as an oxidizing agent.
$2$. Displacement: $2Na[Ag(CN)_2] + Zn \rightarrow Na_2[Zn(CN)_4] + 2Ag$. Here,$Zn$ acts as a reducing agent.
Thus,$O_2$ is the oxidizing agent and $Zn$ powder is the reducing agent.

(D) In the cyanide process for the extraction of silver,silver metal is dissolved in a dilute solution of sodium cyanide $(NaCN)$ in the presence of air (oxygen) to form a soluble complex.
The chemical reaction is as follows:
$4Ag(s) + 8NaCN(aq) + 2H_2O(aq) + O_2(g) \rightarrow 4Na[Ag(CN)_2](aq) + 4NaOH(aq)$
The complex formed is sodium dicyanoargentate$(I)$,which has the formula $Na[Ag(CN)_2]$.

(B) In the Bessemer converter,the molten matte $(Cu_2S + FeS)$ is subjected to oxidation.
First,the remaining $FeS$ is oxidized to $FeO$,which then reacts with silica $(SiO_2)$ to form slag $(FeSiO_3)$.
After the removal of iron,the remaining $Cu_2S$ undergoes self-reduction (autoreduction) by reacting with the $Cu_2O$ formed by the partial oxidation of $Cu_2S$.
The chemical reaction is: $Cu_2S + 2Cu_2O \rightarrow 6Cu + SO_2$.

(D) In the extraction of iron,$CaO$ acts as a flux and combines with $SiO_2$ (impurity) to form slag,$CaSiO_3$. Therefore,the statement that $SiO_2$ is used as a flux is incorrect.

(C) During the extraction of copper from copper pyrites $(CuFeS_2)$,the ore is roasted and then smelted in a blast furnace.
This process results in the formation of a molten mixture of copper$(I)$ sulfide $(Cu_2S)$ and iron$(II)$ sulfide $(FeS)$,which is known as 'matte'.
Therefore,the correct composition of matte is $Cu_2S + FeS$.

(B) In the blast furnace,$Fe_2O_3$ is reduced to iron using carbon monoxide $(CO)$ as the reducing agent at high temperatures.
The chemical reaction is: $Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2$.

(B) The extraction of silver $(Ag)$ from its ore $(Ag_2S)$ involves the formation of a soluble complex salt,sodium dicyanoargentate$(I)$.
The chemical reactions are:
$Ag_2S + 4NaCN \rightleftharpoons 2Na[Ag(CN)_2] + Na_2S$
$2Na[Ag(CN)_2] + Zn \rightarrow Na_2[Zn(CN)_4] + 2Ag \downarrow$

(C) The given chemical equation represents the extraction of gold from its ore using cyanide process (MacArthur-Forrest process).
The balanced chemical equation is: $4Au + 8CN^{-} + 2H_2O + O_2 \to 4[Au(CN)_2]^- + 4OH^{-}$.
Thus,the metal $M$ is Gold $(Au)$.

(B) The correct answer is $B$. The statement that the impurities present in cast iron are oxidised by air is incorrect. In the reverberatory furnace,the impurities in cast iron are primarily oxidised by $Fe_2O_3$ (hematite) added to the mixture,not by air directly.

(C) The extraction of silver and gold involves the cyanide process (MacArthur-Forrest process).
First,the ore is leached with $NaCN$ in the presence of air $(O_2)$ to form a soluble complex:
$Ag_{2}S + 4 NaCN \xrightarrow{O_{2}} 2 Na[Ag(CN)_{2}] + Na_{2}SO_{4}$
Then,the silver is recovered from the solution by displacement using a more electropositive metal like zinc $(Zn)$:
$2 Na[Ag(CN)_{2}] + Zn \longrightarrow Na_{2}[Zn(CN)_{4}] + 2Ag(\downarrow)$
Thus,silver is recovered by displacement with $Zn$.

(B) In the extraction of copper from its sulphide ore,the ore is subjected to roasting,where some of it is oxidized to $Cu_{2}O$.
This $Cu_{2}O$ then reacts with the remaining $Cu_{2}S$ (cuprous sulphide) to produce copper metal.
The chemical equation for this self-reduction process is:
$2Cu_{2}O + Cu_{2}S \longrightarrow 6Cu + SO_{2} \uparrow$
In this reaction,$Cu_{2}S$ acts as the reducing agent for $Cu_{2}O$.

(A) Metals with high affinity for oxygen,such as $Al$,$Mg$,and $Ca$,form very stable oxides.
$Al_2O_3$ cannot be reduced to metal by carbon because aluminum has a higher affinity for oxygen than carbon does at moderate temperatures.
Instead of reduction,aluminum reacts with carbon at very high temperatures to form aluminum carbide $(Al_4C_3)$.

(C) Alumina,$Al_2O_3$,is a poor conductor of electricity and has a very high melting point.
To facilitate electrolysis,it is mixed with cryolite $(Na_3AlF_6)$ and fluorspar $(CaF_2)$.
These substances lower the melting point of the mixture and increase its electrical conductivity,allowing the electrolysis to occur at a lower temperature.

(B) Pig iron is the most impure form of iron,obtained directly from the blast furnace.
It contains about $3-4.5 \%$ of carbon as the major impurity.
Other impurities like $S, P, Si,$ and $Mn$ are present in much smaller amounts compared to carbon.

(C) In the blast furnace,the limestone $(CaCO_3)$ decomposes to form calcium oxide $(CaO)$,which acts as a flux.
This flux reacts with the silica $(SiO_2)$ impurity (gangue) present in the ore to form a fusible slag called calcium silicate $(CaSiO_3)$.
The reaction is: $CaO_{(s)} + SiO_{2(s)} \rightarrow CaSiO_{3(l)}$.

(B) In the Hall-Heroult process,$Al_2O_3$ is dissolved in molten cryolite $(Na_3AlF_6)$ and fluorspar $(CaF_2)$,which lowers the melting point of the mixture and increases electrical conductivity.
$Al^{3+}$ is reduced to $Al$ at the cathode.
Carbon anodes are oxidized to $CO$ and $CO_2$.
$Na_3AlF_6$ (cryolite) acts as a solvent for $Al_2O_3$,not as the electrolyte itself; the mixture of $Al_2O_3$ and cryolite acts as the electrolyte. Therefore,the statement that $Na_3AlF_6$ serves as the electrolyte is technically false as it is a component of the electrolytic mixture.

(D) The reduction of iron oxides to metallic iron is a key step in metallurgy.
In option $D$,the sequence is:
$1. \ 3Fe + 2O_2 \xrightarrow{\Delta} Fe_3O_4$
$2. \ Fe_3O_4 + CO \xrightarrow{600^{\circ}C} 3FeO + CO_2$
$3. \ FeO + CO \xrightarrow{700^{\circ}C} Fe + CO_2$
This sequence correctly represents the extraction of iron from its oxide ore using carbon monoxide as a reducing agent at specific temperatures.

(A) The process described is: Ore $\xrightarrow{\text{Roasting}}$ Metal oxide $\xrightarrow{\text{Carbon reduction}}$ Metal $M$.
$1$. $Zn$ (Zinc) is extracted from its ore (Zinc blende,$ZnS$) by roasting to form $ZnO$,followed by reduction with carbon (coke) to obtain $Zn$.
$2$. $Al$ (Aluminum) cannot be extracted by carbon reduction because it is a highly reactive metal; it is extracted by electrolytic reduction.
$3$. $Hg$ (Mercury) is extracted from Cinnabar $(HgS)$ by roasting,which directly yields $Hg$ metal (self-reduction),not by carbon reduction.
$4$. $Na$ (Sodium) is highly reactive and is extracted by electrolysis of fused $NaCl$.
Therefore,the metal that fits the given sequence is $Zn$.

(C) The solidified copper obtained after the Bessemerisation process is impure and contains impurities like $Fe$,$Ni$,$Zn$,$Ag$,and $Au$.
It has a blistered appearance due to the evolution of $SO_2$ gas during the cooling process,hence it is called blister copper.
Therefore,both statements $A$ and $B$ are correct.

(B) The thermite process involves the reduction of a metal oxide using aluminum powder as a reducing agent,which is highly exothermic.
Specifically,the reaction between metal oxides (like $Fe_2O_3$ or $MnO_2$) and aluminum is used to extract metals.
Option $B$ shows the reduction of manganese dioxide $(MnO_2)$ by aluminum to produce manganese $(Mn)$ and aluminum oxide $(Al_2O_3)$,which is a classic example of the thermite process.
Therefore,the correct option is $B$.

(D) In an Ellingham diagram,the slope of the line $\Delta G^0$ vs $T$ is given by $\Delta S^0$. $A$ change in the slope of the line indicates a phase change of the metal or the oxide.
At point $A$,the metal $M$ undergoes a phase change (melting),which leads to an increase in entropy,thus changing the slope.
At point $B$,the metal oxide $MO_2$ undergoes a phase change (boiling/vaporization),which further changes the slope.
Therefore,points $A$ and $B$ correspond to the melting point and boiling point of the metal/oxide respectively.

(D) The extraction of metals from their ores involves specific metallurgical processes:
$A$. Copper pyrites $(CuFeS_2)$ is concentrated by froth floatation,followed by roasting and smelting in a reverberatory furnace,not reduction by coke.
$B$. Calamine $(ZnCO_3)$ is first calcined to $ZnO$ and then reduced by coke $(C)$,not $CO$.
$C$. Haematite $(Fe_2O_3)$ is reduced by $CO$ in a blast furnace,but it is not concentrated by leaching.
$D$. Red bauxite $(Al_2O_3 \cdot 2H_2O)$ is concentrated by leaching (Bayer's process) to obtain pure alumina,which is then reduced by electrolysis in molten cryolite $(Na_3AlF_6)$. This is the $CORRECT$ match.

(C) Case hardening is a process used to harden the surface of steel by diffusing carbon or nitrogen into the surface layer.
In the process of case hardening using charcoal,steel is heated in an atmosphere of charcoal $(C)$ or carbon-rich materials to increase the carbon content on the surface,making it harder.
Therefore,the correct option is $C$.

(D) In the Ellingham diagram,the slope of the line for the oxidation of a metal $(M \rightarrow MO)$ changes when the metal undergoes a phase change (melting or boiling).
Looking at the provided diagram,the line for $M \rightarrow MO$ shows a distinct change in slope at a certain temperature.
This change in slope indicates a phase transition of the metal $M$.
Since the reaction $MO(s) + C(s) \rightarrow M(?) + CO(g)$ occurs at temperatures where the metal $M$ is produced,the physical state of $M$ depends on whether the temperature is above or below its melting or boiling point.
Typically,such a change in slope in an Ellingham diagram corresponds to the melting of the metal. Therefore,the metal $M$ can exist as a solid or a liquid depending on the temperature range relative to its melting point.

(B) The electrolysis of alumina is carried out in a steel tank lined with graphite,which acts as the cathode.
The electrolyte consists of alumina $(Al_2O_3)$ dissolved in fused cryolite $(Na_3AlF_6)$ and fluorspar $(CaF_2)$.
Cryolite lowers the melting point of the mixture to approximately $950^{\circ}C$.
Fluorspar $(CaF_2)$ is added to increase the fluidity of the molten mass and to make the mixture a better conductor of electricity.
This allows the liberated aluminium metal to sink to the bottom of the cell for easy collection.

(D) The correct option is $D$.
Explanation:
In the Hall-Heroult process,the electrolytic cell is covered with a layer of powdered coke. This layer serves two primary purposes: it acts as an insulator to prevent the loss of heat from the molten electrolyte,and it protects the electrolyte from oxidation by atmospheric oxygen.

(B) In the extraction of copper from copper glance $(Cu_2S)$ or copper sulphide ore,the process is known as self-reduction or auto-reduction.
First,the sulphide ore is partially roasted in air to form copper$(I)$ oxide:
$2Cu_2S + 3O_2 \rightarrow 2Cu_2O + 2SO_2$
Then,the remaining copper sulphide reacts with the copper oxide formed to produce metallic copper:
$2Cu_2O + Cu_2S \rightarrow 6Cu + SO_2$
This is a self-reduction process where copper sulphide acts as a reducing agent for copper oxide. Among the given options,the reaction sequence representing this principle is $2CuO + CuS \rightarrow 3Cu + SO_2$ (simplified representation of the stoichiometry).

(B) The cyanide process is used for the extraction of $Ag$,which is also known as the $McArthur-Forest$ process.
The reactions occurring during the extraction of silver are:
$Ag_2S + 4NaCN \rightleftharpoons 2Na[Ag(CN)_2] + Na_2S$ (Reversible reaction)
$2Na_2S + 2O_2 + H_2O \rightarrow Na_2S_2O_3 + 2NaOH$ (The presence of $O_2$ shifts the equilibrium to the right by removing $Na_2S$)
$2Na[Ag(CN)_2] + Zn \rightarrow Na_2[Zn(CN)_4] + 2Ag$ (Displacement reaction)

(D) The extraction of silver involves several methods:
$1$. Silver is obtained as a byproduct during the electrolytic refining of copper.
$2$. The Parkes process is used to remove silver from lead using $Zn$.
$3$. The Mac-Arthur Forrest cyanide process involves the reaction: $Ag_2S + 4KCN \rightarrow 2K[Ag(CN)_2] + K_2S$,followed by displacement with $Zn$: $2K[Ag(CN)_2] + Zn \rightarrow K_2[Zn(CN)_4] + 2Ag$.
$4$. Heating $Na[Ag(CN)_2]$ does not yield metallic silver; instead,it decomposes into complex products. Therefore,this is not a method for silver extraction.

(C) In the isolation of mercury from cinnabar $(HgS)$,no external reducing agent is required.
Mercury is obtained by the self-reduction method (auto-reduction).
First,cinnabar is roasted in air to form mercury$(II)$ oxide:
$2HgS + 3O_2 \xrightarrow{\Delta} 2HgO + 2SO_2$
Then,the remaining $HgS$ reacts with $HgO$ to produce mercury metal:
$2HgO + HgS \rightarrow 3Hg + SO_2$

(D) Aluminium metal is extracted by the electrolytic reduction of alumina $(Al_2O_3)$.
Since alumina has a very high melting point and is a poor conductor of electricity,it is dissolved in molten cryolite $(Na_3AlF_6)$ and fluorspar $(CaF_2)$.
This mixture melts at approximately $900^{\circ} C$ and allows for the electrolysis process.
During electrolysis,metallic $Al$ is liberated at the cathode.

(C) The iron obtained from the blast furnace is known as pig iron.
It contains about $4 \%$ carbon and many impurities in smaller amounts (like $S, P, Si, Mn$).
It has a higher carbon content compared to cast iron and wrought iron.

(A) $(i)$. In Downs cell,the electrolyte used is a fused mixture of $40\% NaCl$ and $60\% CaCl_2$ to lower the melting point.
$(ii)$. In the Dow sea water process,magnesium is extracted from sea water,and the electrolyte used is fused $MgCl_2$.
$(iii)$. In the Hall-Heroult process,the electrolyte used is a fused mixture of $Al_2O_3$ and $Na_3AlF_6$ (cryolite).
$(iv)$. In the Moissan process,the electrolyte used is fused $KHF_2$ for the preparation of fluorine.
Therefore,the correct match is $(i-Z, ii-W, iii-X, iv-Y)$.

(C) In the extraction of chromium from chromite ore $(FeCr_2O_4)$,the ore is fused with $NaOH$ in the presence of air to form sodium chromate $(Na_2CrO_4)$ and iron$(III)$ oxide $(Fe_2O_3)$.
$Na_2CrO_4$ is a soluble salt,whereas $Fe_2O_3$ is an insoluble metal oxide.
Therefore,the mixture can be separated by dissolving the mass in water $(H_2O)$,where $Na_2CrO_4$ dissolves and $Fe_2O_3$ remains as a residue.

(A) $I$. $4FeCr_2O_4 + 16NaOH + 7O_2 \rightarrow 8Na_2CrO_4 + 2Fe_2O_3 + 8H_2O$. Here,$(A)$ is $Na_2CrO_4$.
$II$. $2Na_2CrO_4 + 2H^+ \rightarrow Na_2Cr_2O_7 + 2Na^+ + H_2O$. Here,$(B)$ is $H^+$.
$III$. $Na_2Cr_2O_7 + 2C \rightarrow Cr_2O_3 + Na_2CO_3 + CO$. Here,$X$ is $C$.
$IV$. $Cr_2O_3 + 2Al \rightarrow 2Cr + Al_2O_3$. Here,$Y$ is $Al$.
For highly reactive metals like $Al$ (Aluminum),which are at the top of the electrochemical series,electrolytic reduction is required at high temperatures (Hall-Heroult process) because they cannot be reduced by common reducing agents like $C$ or $CO$.

(C) In the extraction of copper,the Bessemer converter is used to convert copper matte $(Cu_2S + FeS)$ into blister copper.
The reactions occurring in the Bessemer converter are:
$1. \ 2FeS + 3O_2 \rightarrow 2FeO + 2SO_2$
$2. \ FeO + SiO_2 \rightarrow FeSiO_3$ (Slag formation)
$3. \ 2Cu_2S + 3O_2 \rightarrow 2Cu_2O + 2SO_2$
$4. \ 2Cu_2O + Cu_2S \rightarrow 6Cu + SO_2$
The reaction $2CuFeS_2 + O_2 \rightarrow Cu_2S + 2FeS + SO_2$ occurs during the roasting process in a reverberatory furnace,not in the Bessemer converter.

(B) In the cyanide process for the extraction of silver,the ore is treated with a dilute solution of $NaCN$ in the presence of air to form a soluble complex: $4Ag + 8CN^- + 2H_2O + O_2 \rightarrow 4[Ag(CN)_2]^- + 4OH^-$.
Zinc is then added to this solution to displace silver from the complex: $2[Ag(CN)_2]^- + Zn \rightarrow [Zn(CN)_4]^{2-} + 2Ag$.
In this reaction,$Zn$ is oxidized to $Zn^{2+}$ and $Ag^+$ is reduced to $Ag$. Therefore,zinc acts as a reducing agent.