Reduction to free Metal Questions in English

(A) The Ellingham diagram is a graphical representation of the change in Gibbs free energy $(\Delta G)$ of formation of oxides,sulfides,and halides of elements as a function of temperature $(T)$.
It is essentially a plot of $\Delta G$ versus $T$ for the oxidation or reduction reactions of metals.
This diagram helps in predicting the feasibility of thermal reduction of metal oxides.

(D) In the extraction of iron,$SiO_2$ is present as an acidic impurity. To remove it,a basic flux like $CaO$ is added.
The reaction is: $\mathop {CaO}\limits_{\text{Flux}} + \mathop {SiO_2}\limits_{\text{Impurity}} \to \mathop {CaSiO_3}\limits_{\text{Slag}}$
Thus,the slag produced is $CaSiO_3$.

(C) In the aluminothermite process,metal oxides (like $Cr_2O_3$ or $Fe_2O_3$) are reduced to their respective metals using aluminium powder.
The chemical reaction is: $Cr_2O_3 + 2Al \to Al_2O_3 + 2Cr$.
In this reaction,aluminium $(Al)$ gets oxidised to $Al_2O_3$ and reduces the metal oxide to metal. Therefore,$Al$ acts as a reducing agent.

(D) $1$. $CuFeS_2$ (Copper pyrites) is concentrated by froth flotation,not leaching.
$2$. $Au$ (Gold) is purified by zone refining or electrolytic refining,not polling.
$3$. $Fe_2O_3$ (Hematite) is reduced by carbon (smelting) in a blast furnace,not electrolysis.
$4$. $PbS$ (Galena) is extracted by roasting to form $PbO$,which then reacts with remaining $PbS$ to produce lead metal. This process is known as self-reduction or auto-reduction. Thus,$PbS - \text{Reduction} - \text{Self reduction}$ is the correct match.

(A) In the Ellingham diagram,the point of intersection of two lines represents the temperature at which the two metals (or a metal and carbon) have an equal affinity for oxygen.
The line for the oxidation of zinc $(2Zn + O_2 \rightarrow 2ZnO)$ and the line for the oxidation of carbon $(2C + O_2 \rightarrow 2CO)$ intersect at $1000^{\circ}C$.
Therefore,at $1000^{\circ}C$,zinc and carbon have equal affinity for oxygen.

(B) In an Ellingham diagram,a metal oxide can be reduced by a reducing agent if the $\Delta G^\circ$ line of the reducing agent lies below the $\Delta G^\circ$ line of the metal oxide at a given temperature.
The reduction reaction is $ZnO + C \to Zn + CO$.
From the provided Ellingham diagram,the line for the oxidation of carbon $(2C + O_2 \to 2CO)$ intersects the line for the oxidation of zinc $(2Zn + O_2 \to 2ZnO)$ at approximately $1000 \, ^\circ C$.
For temperatures above $1000 \, ^\circ C$,the $\Delta G^\circ$ line for the formation of $CO$ lies below the $\Delta G^\circ$ line for the formation of $ZnO$. Therefore,carbon can act as a reducing agent for $ZnO$ only at temperatures greater than $1000 \, ^\circ C$.

(D) In an Ellingham diagram,a metal can reduce the oxide of another metal if the former's oxidation line lies below the latter's line at a given temperature.
At $1100 \, ^oC$,the line for the formation of $MgO$ is significantly below the line for the formation of $ZnO$.
Therefore,$Mg$ can effectively reduce $ZnO$ to $Zn$.
The reaction $ZnO + Mg \to MgO + Zn$ has the most negative Gibbs free energy change $(\Delta G)$ among the given options,making it the most spontaneous reaction.

(B) Metals lying above $H$ in the electrochemical series are not obtained from their oxides by simple heating.
On heating,$ZnO$ will not give $Zn$ metal because $Zn$ is a moderately reactive metal.
However,it can be reduced with $C$ or $H_2$ to give the free metal:
$ZnO + C \rightarrow Zn + CO$
$ZnO + CO \rightarrow Zn + CO_2$
$ZnO + H_2 \xrightarrow{\text{above } 400^{\circ} C} Zn + H_2O$
In contrast,$HgO$ and $Ag_2O$ are oxides of noble metals and decompose upon heating to give $Hg$ and $Ag$ respectively:
$2HgO \rightarrow 2Hg + O_2$
$2Ag_2O \rightarrow 4Ag + O_2$

(B) In the extraction of copper from copper glance $(Cu_2S)$,the ore is roasted in a limited supply of air to partially convert $Cu_2S$ into $Cu_2O$:
$2Cu_2S + 3O_2 \to 2Cu_2O + 2SO_2$
After roasting,the temperature is increased to carry out self-reduction (auto-reduction),where the remaining $Cu_2S$ acts as a reducing agent for $Cu_2O$:
$2Cu_2O + Cu_2S \to 6Cu + SO_2$
This process is known as self-reduction or auto-reduction.

(D) The reduction of a metal oxide by carbon is thermodynamically feasible only if the Gibbs free energy change $(\Delta G)$ for the reaction is negative.
$Al_2O_3$ has a very high negative enthalpy of formation,meaning it is extremely stable.
Carbon cannot reduce $Al_2O_3$ to $Al$ because the affinity of $Al$ for oxygen is much higher than that of $C$ for oxygen at moderate temperatures.
Therefore,the enthalpy of formation of $Al_2O_3$ is too high for carbon to act as a reducing agent.

(B) In the process of metallurgy,a flux is added to remove gangue (impurities).
Flux reacts with gangue to form a fusible material called slag.
For example,if the impurity is $SiO_2$ (acidic),a basic flux like $CaO$ is added.
$CaO + SiO_2 \rightarrow CaSiO_3$ (Calcium silicate).
Thus,the slag consists of molten impurities generally in the form of metal silicate.

(D) In the extraction of copper from copper pyrite $(CuFeS_2)$,the ore is roasted to convert iron sulfide into ferrous oxide $(FeO)$.
$FeO$ is a basic impurity.
To remove this basic impurity,an acidic flux,$SiO_2$,is added.
$FeO + SiO_2 \rightarrow FeSiO_3$ (slag).
Thus,$SiO_2$ is used as the flux.

(D) flux is a substance added to the ore during smelting to remove gangue (impurities).
If the gangue is acidic (e.g.,$SiO_2$),a basic flux (e.g.,$CaO$) is added to form a fusible slag $(CaSiO_3)$.
If the gangue is basic (e.g.,$FeO$),an acidic flux (e.g.,$SiO_2$) is added to form a fusible slag $(FeSiO_3)$.
Therefore,a flux is used to remove both acidic and basic impurities depending on the nature of the gangue present in the ore.

(A) The alumino-thermite process is used for the extraction of metals like $Cr$ and $Mn$ from their oxides using aluminium powder as a reducing agent.
To initiate the reaction,an ignition mixture is required to provide the necessary heat.
This ignition mixture consists of magnesium powder and barium peroxide $(BaO_2)$.

(B) Smelting is a process of reduction in which the roasted or calcined ore is mixed with a suitable flux and fuel and then heated to a high temperature above its melting point. In this process,the metal oxide is reduced to its metallic state by a reducing agent like carbon or carbon monoxide.

(C) The blast furnace is used for the extraction of iron from its ore.
Because the temperature inside the blast furnace is extremely high,the inner lining must be made of materials that can withstand high heat without melting or reacting.
These are known as fire bricks or refractory bricks,which are primarily composed of alumina $(Al_2O_3)$ and silica $(SiO_2)$.

(B) Silica $(SiO_2)$ is an acidic impurity (gangue). To remove an acidic impurity,a basic flux is required. The basic flux reacts with the acidic impurity to form a fusible slag. For example,$CaO$ (basic flux) reacts with $SiO_2$ (acidic impurity) to form $CaSiO_3$ (slag).

(D) Highly reactive metals like $Al$,$Na$,$Mg$,and $Ca$ are extracted by the electrolytic reduction of their fused salts because they cannot be reduced by carbon or other common reducing agents.
$Al$ is extracted by the Hall-$H$éroult process,which involves the electrolytic reduction of alumina $(Al_2O_3)$ dissolved in molten cryolite $(Na_3AlF_6)$.

(A) The most common and economical method for the extraction of metals from their oxide ores is reduction by carbon. In this process,the metal oxide is heated with coke (carbon),which acts as a reducing agent to produce the metal and carbon monoxide or carbon dioxide. This is widely used for metals like $Fe$,$Zn$,$Pb$,etc.

(A) In metallurgy,a basic lining is required in furnaces where basic impurities (like $P_4O_{10}$) are to be removed or when the slag formed is acidic. $MgO \cdot CaO$ (calcined dolomite) or $MgO$ (magnesia) are commonly used as basic refractory materials for lining the furnace.

(D) The cyanide process,also known as the Mac-Arthur Forrest process,is used for the extraction of gold $(Au)$ and silver $(Ag)$ from their ores.
In this process,the crushed ore is treated with a dilute solution of sodium cyanide $(NaCN)$ in the presence of air $(O_2)$,which acts as an oxidizing agent.
The metal dissolves in the cyanide solution to form a soluble complex:
$4M + 8CN^- + 2H_2O + O_2 \rightarrow 4[M(CN)_2]^- + 4OH^-$ (where $M = Au$ or $Ag$).
Therefore,both $Au$ and $Ag$ are extracted using this method.

(B) In the process of metallurgy,specifically in the thermite process,aluminum is used to reduce metal oxides (like $Cr_2O_3$ or $Fe_2O_3$) to their respective metals.
Since aluminum undergoes oxidation $(Al \rightarrow Al^{3+} + 3e^-)$ and reduces the metal oxide,it acts as a strong reducing agent.

(C) In the Hall-Heroult process for the extraction of aluminum,pure $Al_2O_3$ is mixed with $Na_3AlF_6$ (cryolite) and $CaF_2$ (fluorspar).
This mixture is used as the electrolyte because it lowers the melting point of the mixture and increases its electrical conductivity.
Therefore,the correct option is $C$.

(B) The extraction of $Pb$ (lead) from its ore galena $(PbS)$ is primarily carried out by the self-reduction process (also known as air reduction).
In this process,$PbS$ is partially roasted to form $PbO$,which then reacts with the remaining $PbS$ to produce $Pb$ metal: $2PbS + 3O_2 \rightarrow 2PbO + 2SO_2$ and $PbS + 2PbO \rightarrow 3Pb + SO_2$.
The extraction of $Sn$ (tin) from its ore cassiterite $(SnO_2)$ is carried out by carbon reduction,where $SnO_2$ is heated with coke (carbon) in a furnace: $SnO_2 + 2C \rightarrow Sn + 2CO$.

(A) In metallurgy,flux is a substance added to the ore to remove gangue (impurities).
It reacts with infusible impurities (gangue) to form a fusible material known as slag.
Thus,the process converts infusible impurities into fusible impurities,which can be easily removed from the molten metal.

(B) In the blast furnace,the reduction of iron oxides ($Fe_2O_3$ and $Fe_3O_4$) occurs primarily by $CO$ gas at lower temperatures $(500-800 \ K)$.
The reaction is: $Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2$.
At higher temperatures $(> 1073 \ K)$,carbon $(C)$ also acts as a reducing agent,but $CO$ is the primary reducing agent in the upper cooler parts of the furnace.

(B) During the extraction of metals like $Fe$ (iron) and $Cu$ (copper),a flux is added to remove gangue impurities.
The flux reacts with the gangue to form a fusible material called slag.
Slag is essentially a silicate or phosphate compound.
Properties of slag:
$1$. It is lighter than the molten metal,so it floats on the surface of the molten metal,protecting it from oxidation.
$2$. It has a lower melting point than the metal,allowing it to remain in a liquid state for easy removal.

(C) The alumino-thermite process involves the reduction of metal oxides (like $Cr_2O_3$ or $Fe_2O_3$) using aluminum powder as a reducing agent.
This process is highly exothermic and is commonly used for the extraction of metals like $Cr$ and $Mn$ from their respective oxides.
Therefore,among the given options,$Cr$ is the correct metal extracted via this method.

(B) Cryolite is $Na_3AlF_6$.
In the Hall-$H$éroult process,pure alumina $(Al_2O_3)$ has a very high melting point $(2323 \ K)$.
Adding cryolite $(Na_3AlF_6)$ lowers the melting point of the mixture to about $1240 \ K$ and also increases the electrical conductivity of the melt,making the electrolysis process more efficient.

(C) In the metallurgy of copper,the sulfide ore is first roasted to form $Cu_2O$ and $Cu_2S$.
Some $Cu_2O$ reacts with $Cu_2S$ in a process known as self-reduction (or auto-reduction) to produce copper metal.
The chemical reaction is: $2Cu_2O + Cu_2S \rightarrow 6Cu + SO_2$.

(A) The self-reduction method (also known as auto-reduction) is used for the extraction of metals that have low affinity for oxygen,such as $Cu$,$Hg$,and $Pb$.
For copper,the reaction is: $2Cu_2S + 3O_2 \rightarrow 2Cu_2O + 2SO_2$ followed by $2Cu_2O + Cu_2S \rightarrow 6Cu + SO_2$.
For mercury,the reaction is: $2HgS + 3O_2 \rightarrow 2HgO + 2SO_2$ followed by $2HgO + HgS \rightarrow 3Hg + SO_2$.
Therefore,$Cu$ and $Hg$ are extracted using this method.

(B) In metallurgy,a flux is added to remove gangue (impurities) from the ore.
If the impurity is acidic (e.g.,$SiO_2$),a basic flux is used.
If the impurity is basic (e.g.,$FeO$),an acidic flux is used.
Limestone $(CaCO_3)$ acts as a basic flux because it decomposes to form calcium oxide $(CaO)$,which reacts with acidic silica $(SiO_2)$ to form slag $(CaSiO_3)$:
$CaCO_3 \rightarrow CaO + CO_2$
$CaO + SiO_2 \rightarrow CaSiO_3$ (slag).
Therefore,limestone is used to remove acidic impurities.

(C) An $Electric \ furnace$ uses electrical energy to generate heat,which allows it to reach significantly higher temperatures (often exceeding $3000 \ ^\circ C$) compared to fuel-fired furnaces like the blast furnace,reverberatory furnace,or muffle furnace. Therefore,the correct option is $C$.

(B) During the extraction of copper from copper pyrites $(CuFeS_2)$,the ore is roasted to remove sulfur and then smelted in a blast furnace.
In the furnace,iron oxide $(FeO)$ is formed as an impurity.
Silica $(SiO_2)$ is added as a flux to remove this impurity.
$FeO + SiO_2 \rightarrow FeSiO_3$ (slag).
Thus,the slag formed is iron silicate $(FeSiO_3)$.

(C) During the extraction of iron in a blast furnace,limestone $(CaCO_3)$ is added as a flux.
It decomposes to form calcium oxide $(CaO)$.
$CaO$ reacts with the impurity silica $(SiO_2)$ present in the ore to form calcium silicate $(CaSiO_3)$,which is the slag.
$CaO + SiO_2 \rightarrow CaSiO_3$ (Slag).

(C) Highly reactive metals like $Ca$,$Mg$,and $Al$ are extracted by the electrolysis of their fused salts because they cannot be reduced by carbon or other common reducing agents.
$Cr$ (Chromium) is typically obtained by the reduction of its oxide $(Cr_2O_3)$ with aluminum (Alumino-thermic process) or by other chemical reduction methods,not by electrolysis of its salt in the extraction process.

(D) In the process of metallurgy,a substance called $Flux$ is added to the ore to remove the impurities (gangue).
$Flux$ reacts with the gangue to form a fusible material known as $Slag$.
Therefore,the substance added is $Flux$.

(C) In the hydrometallurgical process for the extraction of silver,$Na[Ag(CN)_2]$ is formed by the leaching of silver ore with $NaCN$ solution.
To recover silver from this complex,a more electropositive metal like zinc $(Zn)$ is added.
The displacement reaction is: $2Na[Ag(CN)_2] + Zn \rightarrow Na_2[Zn(CN)_4] + 2Ag$.
Since $Zn$ is more reactive than $Ag$,it displaces silver from the complex.

(A) The extraction of gold involves leaching the ore with a dilute solution of $NaCN$ or $KCN$ in the presence of air $(O_2)$,which provides $O_2$ to oxidize gold to $Au^+$.
The chemical reaction is:
$4Au(s) + 8CN^-(aq) + 2H_2O(aq) + O_2(g) \to 4[Au(CN)_2]^-(aq) + 4OH^-(aq)$
Here,$X$ is $[Au(CN)_2]^-$.
Gold is then recovered from this complex by displacement using zinc $(Zn)$:
$2[Au(CN)_2]^-(aq) + Zn(s) \to [Zn(CN)_4]^{2-}(aq) + 2Au(s)$
Here,$Y$ is $[Zn(CN)_4]^{2-}$.
Thus,$X = [Au(CN)_2]^-$ and $Y = [Zn(CN)_4]^{2-}$.

(D) In the metallurgy of copper,the concentrated ore is roasted in a reverberatory furnace.
After roasting,the ore is smelted with silica $(SiO_2)$ and coke.
During this process,iron oxide $(FeO)$ reacts with silica to form iron silicate slag $(FeSiO_3)$.
The remaining copper sulfide $(Cu_2S)$ and some unreacted iron sulfide $(FeS)$ form a molten mixture known as matte.
Therefore,matte is a mixture of $Cu_2S + FeS$.

(C) In a blast furnace,the combustion zone (also known as the tuyere zone) is located at the bottom where hot air is blasted into the furnace.
This region has the highest temperature,reaching approximately $2000 \ K$ to $2200 \ K$,due to the exothermic reaction of coke with oxygen: $C + O_2 \rightarrow CO_2 + \text{Heat}$.

(B) The plots of $\Delta G$ (Gibbs free energy change) versus $T$ (temperature) are known as Ellingham diagrams. These diagrams were first used by Harold Ellingham to evaluate the feasibility of metal oxide reduction by various reducing agents.

(A) The conversion of pig iron into cast iron (or wrought iron) involves the removal of impurities like $C$,$Si$,$Mn$,$S$,and $P$ by oxidation. In the reverberatory furnace,the hearth is lined with $Fe_2O_3$. This $Fe_2O_3$ oxidizes the carbon present in the pig iron to carbon monoxide $(CO)$:
$Fe_2O_3 + 3C \rightarrow 2Fe + 3CO$.

(B) In the Bessemer converter,the molten matte $(Cu_2S + FeS)$ is subjected to a blast of air.
First,the remaining $FeS$ is oxidized to $FeO$,which then reacts with silica $(SiO_2)$ to form slag.
After the removal of iron,the remaining $Cu_2S$ undergoes self-reduction (autoreduction) in the presence of air:
$2Cu_2S + 3O_2 \to 2Cu_2O + 2SO_2$
$2Cu_2O + Cu_2S \to 6Cu + SO_2$
Both reactions $C$ and $B$ occur in the converter,but the primary reaction that leads to the formation of metallic copper via self-reduction is $2Cu_2O + Cu_2S \to 6Cu + SO_2$.

(B) Smelting is a process of reduction of a metal oxide with carbon at high temperatures.
In the given options,the reaction $Fe_2O_3 + 3C \to 2Fe + 3CO$ represents the reduction of iron oxide by carbon,which is the characteristic reaction of the smelting process in a blast furnace.
Option $A$ represents calcination/dehydration.
Option $C$ represents calcination.
Option $D$ represents roasting.

(D) Highly electropositive metals (such as $Na, K, Mg, Ca, Al$) have a very high affinity for oxygen and cannot be reduced by common reducing agents like carbon or carbon monoxide.
Therefore,these metals are extracted by the electrolysis of their molten ionic salts (fused chlorides or oxides),where the metal is deposited at the cathode.

(D) Bessemerization is a process used in the metallurgy of copper $(Cu)$.
In this process,molten matte $(Cu_2S + FeS)$ is taken in a Bessemer converter.
Air is blown through the molten matte to oxidize $FeS$ to $FeO$,which then reacts with silica $(SiO_2)$ to form slag $(FeSiO_3)$.
Finally,the remaining $Cu_2S$ is reduced to metallic copper,known as blister copper.

(D) In the extraction of zinc,zinc oxide $(ZnO)$ is reduced by coke $(C)$ at high temperatures $(1673 \ K)$:
$ZnO + C \rightarrow Zn + CO$
Here,the carbon monoxide $(CO)$ gas produced escapes and burns at the mouth of the furnace with a characteristic blue flame.

(D) The extraction of copper from copper pyrites $(CuFeS_2)$ involves roasting in a blast furnace. $CuFeS_2$ is converted into $Cu_2S$ and $FeO$. $FeO$ is then removed as slag by adding silica $(SiO_2)$ to form $FeSiO_3$. The principle behind this process is that at high temperatures,iron has a greater affinity for oxygen than sulfur,allowing it to be selectively oxidized and removed as slag,while copper remains as a sulfide.