Reduction to free Metal Questions in English

(C) According to the Ellingham diagram,the reduction of $Al_2O_3$ by $Mg$ is thermodynamically feasible because the curve for the formation of $MgO$ lies below the curve for the formation of $Al_2O_3$ at temperatures below $1665 \ K$.
However,the use of magnesium as a reducing agent for the extraction of aluminium is not economical due to the high cost of magnesium compared to the value of the aluminium produced.
Therefore,statement $3$ is incorrect.

(B) Limestone $(CaCO_3)$ is used as a flux in the extraction of $Fe$ from haematite in a blast furnace.
It decomposes to $CaO$,which acts as the flux to remove the silicate impurity (gangue) present in the ore as molten slag.
$CaCO_3 \xrightarrow{\Delta} CaO + CO_2$
$CaO + SiO_2 \xrightarrow{\Delta} CaSiO_3$ (slag)

(A) In the extraction of iron from haematite $(Fe_2O_3)$,the main impurity present is silica $(SiO_2)$,which is acidic in nature.
To remove this acidic impurity,a basic flux,limestone $(CaCO_3)$,is added.
At high temperatures,$CaCO_3$ decomposes to form $CaO$ $(CaCO_3 \rightarrow CaO + CO_2)$.
The $CaO$ (flux) reacts with $SiO_2$ (impurity) to form calcium silicate $(CaSiO_3)$,which is known as slag.
Thus,$x = SiO_2$ and $y = CaSiO_3$.

(D) In the blast furnace,the temperature range of $500-800 \ K$ is the lower temperature zone.
In this zone,the following reduction reactions occur:
$(i)$ $3 Fe_2O_3 + CO \rightarrow 2 Fe_3O_4 + CO_2$
$(iii)$ $Fe_3O_4 + 4 CO \rightarrow 3 Fe + 4 CO_2$
$(iv)$ $Fe_2O_3 + CO \rightarrow 2 FeO + CO_2$
Reaction $(ii)$ is not a primary reduction step in this specific temperature range.
Therefore,the correct reactions are $(i)$,$(iii)$,and $(iv)$.

(B) The iron obtained from a blast furnace contains about $4 \%$ carbon and many impurities in smaller amounts (e.g.,$S, P, Si, Mn$).
This form of iron is known as pig iron.

(B) In the blast furnace,the reduction of iron oxides occurs at different temperature ranges.
At the temperature range of $900-1500 \ K$ (lower part of the furnace),the following reactions take place:
$FeO + CO \rightarrow Fe + CO_2$
$C + CO_2 \rightarrow 2CO$
$CaO + SiO_2 \rightarrow CaSiO_3$ (slag formation).
Thus,the reaction $FeO + CO \rightarrow Fe + CO_2$ occurs in this zone.

(D) In the Hall-Heroult process for the extraction of aluminium from alumina $(Al_2O_3)$,the following reactions occur:
At the cathode: $Al^{3+} + 3e^- \rightarrow Al(l)$
At the anode: $C(s) + O^{2-} \rightarrow CO(g) + 2e^-$ and $C(s) + 2O^{2-} \rightarrow CO_2(g) + 4e^-$
Statements $(1)$,$(2)$,and $(3)$ are correct: Cryolite $(Na_3AlF_6)$ is added to $Al_2O_3$ to lower its melting point and increase electrical conductivity. $A$ steel vessel with a carbon lining acts as the cathode,and graphite rods act as the anode.
Statement $(4)$ is incorrect because $CO_2$ gas is generated at the anode due to the oxidation of the carbon rods,not at the cathode.

(B) Iron ores contain acidic impurities like silica $(SiO_2)$.
These impurities react with calcium carbonate $(CaCO_3)$ to form molten slag.
The chemical reaction is as follows:
$CaCO_3 + SiO_2 \rightarrow CaSiO_3 + CO_2 \uparrow$
Here,$CaSiO_3$ (calcium silicate) is the slag formed.

(A) In the metallurgy of copper,copper pyrites $(CuFeS_2)$ are roasted to remove sulfur as $SO_2$ and convert iron to $FeO$,which is removed as slag $FeSiO_3$ by adding silica $(SiO_2)$.
After this,the remaining copper matte contains $Cu_2S$ and some $FeS$.
This matte is subjected to Bessemerization,where $Cu_2S$ reacts with the remaining $Cu_2O$ (formed by partial oxidation of $Cu_2S$) to produce metallic copper:
$2Cu_2O + Cu_2S \rightarrow 6Cu + SO_2$.
This process is known as self-reduction or auto-reduction.

(B) During the extraction of copper from copper pyrites $(CuFeS_2)$,the ore is roasted in a reverberatory furnace. The resulting mixture,known as copper matte,consists mainly of cuprous sulfide $(Cu_2S)$ and ferrous sulfide $(FeS)$.
$2CuFeS_2 + O_2 \longrightarrow Cu_2S + 2FeS + SO_{2(g)}$

(A) The reduction of a metal oxide is represented by the reaction: $MO(s/l) + C(s) \rightarrow M(s/l) + CO(g)$.
According to the Gibbs free energy equation,$\Delta G = \Delta H - T\Delta S$.
For the reaction to be spontaneous,$\Delta G$ must be negative.
When the metal oxide is in the liquid state,the entropy of the system is higher compared to the solid state.
Consequently,the entropy change $(\Delta S)$ for the reduction process becomes more positive (or less negative) when the reactant is in the liquid state,making the term $-T\Delta S$ more negative,which facilitates the reduction process.

(C) Copper matte is a mixture of $Cu_2S$ and $FeS$.
During the smelting of roasted copper ore (copper pyrites,$CuFeS_2$),the ore is heated with silica $(SiO_2)$ in a blast furnace.
The iron oxide $(FeO)$ formed reacts with silica to form slag $(FeSiO_3)$,while the remaining $Cu_2S$ and $FeS$ form the molten copper matte.
$2CuFeS_2 + O_2 \longrightarrow Cu_2S + 2FeS + SO_2$

(C) In the electrolytic reduction of alumina (Hall-Heroult process),the molten electrolyte contains $Al_2O_3$ dissolved in cryolite $(Na_3AlF_6)$.
At the cathode,the reduction of aluminum ions takes place:
$Al^{3+} + 3e^- \longrightarrow Al$

(C) Copper matte is obtained during the extraction of copper from copper pyrites.
It is primarily a mixture of copper$(I)$ sulphide $(Cu_2S)$ and iron$(II)$ sulphide $(FeS)$.

(C) The Ellingham diagram is a graphical representation showing the temperature dependence of the stability of compounds,typically metal oxides and sulfides.
It plots the change in standard Gibbs free energy of formation $(\Delta G^{\circ})$ against temperature $(T)$.
This diagram is used to predict the feasibility of the reduction of metal oxides by various reducing agents.

(A) The extraction of gold involves the leaching of gold metal with cyanide ions in the presence of air $(O_2)$ to form the soluble complex $A$:
$4 Au_{(s)} + 8 CN^{-}_{(aq)} + 2 H_2O_{(aq)} + O_{2(g)} \longrightarrow 4 [Au(CN)_2]^{-}_{(aq)} (A) + 4 OH^{-}_{(aq)}$
Next,the gold is recovered from the complex by displacement with a more electropositive metal like zinc,forming the complex $B$:
$2 [Au(CN)_2]^{-}_{(aq)} + Zn_{(s)} \longrightarrow [Zn(CN)_4]^{2-}_{(aq)} (B) + 2 Au_{(s)}$
Thus,$A$ is $[Au(CN)_2]^{-}$ and $B$ is $[Zn(CN)_4]^{2-}$.
Therefore,option $A$ is the correct answer.

(C) The extraction of silver from argentite $(Ag_2S)$ involves the following steps:
$1$. Leaching: $4Ag + 8CN^- + 2H_2O + O_2 \longrightarrow 4[Ag(CN)_2]^- + 4OH^-$. Here,$O_2$ acts as an oxidising agent.
$2$. Precipitation: $2[Ag(CN)_2]^- + Zn \longrightarrow 2Ag + [Zn(CN)_4]^{2-}$. Here,$Zn$ dust acts as a reducing agent.
Thus,$O_2$ is the oxidising agent and $Zn$ dust is the reducing agent.

(B) Statement-$I$ is correct: The Ellingham diagram is a plot of $\Delta G^{\ominus}$ versus $T$ for the formation of oxides. It helps in selecting a suitable reducing agent because a metal can reduce the oxide of another metal if the $\Delta G^{\ominus}$ for the reduction reaction is negative. This occurs when the line for the reducing agent lies below the line for the metal oxide in the Ellingham diagram.
Statement-$II$ is incorrect: In the Ellingham diagram,a more negative value of $\Delta G^{\ominus}$ indicates greater stability of the metal oxide. Therefore,a metal oxide with a lower (more negative) $\Delta G^{\ominus}$ is more stable than an oxide with a higher (less negative) $\Delta G^{\ominus}$.

(A) According to the Ellingham diagram,the line for the formation of $MgO$ lies below the line for the formation of $Al_2O_3$ at temperatures below $1350^{\circ} C$.
Therefore,$Mg$ can reduce $Al_2O_3$ to $Al$ below $1350^{\circ} C$.
Above $1350^{\circ} C$,the line for $Al_2O_3$ formation lies below the line for $MgO$ formation.
Consequently,$Al$ can reduce $MgO$ to $Mg$ above $1350^{\circ} C$.
Since both statements contradict these facts,both $(A)$ and $(B)$ are wrong.

(B) $SiO_2$ (silica) is used as an acid flux in metallurgy.
It reacts with basic gangue (like $CaO$) to form slag $(CaSiO_3)$.

(C) In the extraction of iron from its ore (hematite,$Fe_2O_3$),the main impurity present is silica $(SiO_2)$,which is acidic in nature.
To remove this acidic impurity,a basic flux,limestone $(CaCO_3)$,is added.
Inside the blast furnace,$CaCO_3$ decomposes to form calcium oxide $(CaO)$,which reacts with $SiO_2$ to form a fusible slag,calcium silicate $(CaSiO_3)$.
The reactions are:
$CaCO_3 \rightarrow CaO + CO_2$
$CaO + SiO_2 \rightarrow CaSiO_3$ (slag).
Thus,$X = SiO_2$ and $Y = CaCO_3$.

(A) Molten $Al_2O_3 + Na_3AlF_6$ as electrolyte,carbon coated steel vessel cathode,and graphite anode are used to produce aluminium $(Al)$ by electrolysis.
This process is known as the Hall-$H$éroult process.
In this process,purified alumina is mixed with $Na_3AlF_6$ (cryolite),which lowers the melting point of the mixture and increases its electrical conductivity.
In the electrolytic cell,the steel vessel acts as the cathode (coated with carbon),and graphite rods act as the anode.
The overall reaction is $2Al_2O_3 + 3C \longrightarrow 4Al + 3CO_2 \uparrow$.
The electrolytic reactions are as follows:
$Al_2O_3 \longrightarrow 2Al^{3+} + 3O^{2-}$.
At cathode: $Al^{3+} + 3e^{-} \longrightarrow Al_{(l)}$.
At anode: $C_{(s)} + 2O^{2-} \longrightarrow CO_{2(g)} + 4e^{-}$.
The oxygen liberated at the anode reacts with the carbon of the anode to produce $CO_2$.
Hence,option $(A)$ is the correct answer.

(C) Iron is extracted from its ore,haematite $(Fe_2O_3)$,in a blast furnace. The ore is fed into the top of the furnace along with coke and limestone.
Carbon monoxide acts as a reducing agent during the reaction in the blast furnace,and limestone $(CaCO_3)$ decomposes in the hot furnace to form calcium oxide $(CaO)$.
Calcium oxide reacts with the silica $(SiO_2)$ impurity present in the ore to form a molten slag.
The chemical reaction is:
$CaO + SiO_2 \longrightarrow CaSiO_3$
Thus,the slag formed is calcium silicate $(CaSiO_3)$.

(C) The reaction between $Cu_2O$ and $Cu_2S$ is a self-reduction process used in the extraction of copper.
The chemical equation is: $2Cu_2O + Cu_2S \longrightarrow 6Cu + SO_2$.
In this process,cuprous sulphide $(Cu_2S)$ acts as a reducing agent for cuprous oxide $(Cu_2O)$.
This reaction occurs in the $Bessemer$ converter during the metallurgy of copper.

(D) During the extraction of iron from haematite ore $(Fe_2O_3)$,the roasted ore is mixed with coke and limestone and heated in a blast furnace.
Coke acts as a reducing agent to reduce iron oxides to metallic iron.
Limestone $(CaCO_3)$ decomposes to form calcium oxide $(CaO)$,which acts as a flux.
This flux reacts with acidic impurities like silica $(SiO_2)$ present in the ore to form calcium silicate $(CaSiO_3)$,which is known as slag.
Therefore,the role of limestone is to act as a flux.

(D) In the extraction of silver by the cyanide process (also known as the Mac-Arthur Forrest process),the silver ore is treated with a dilute solution of $NaCN$ in the presence of air to form a soluble complex,$Na[Ag(CN)_2]$.
The chemical reaction is: $Ag_2S + 4NaCN \rightleftharpoons 2Na[Ag(CN)_2] + Na_2S$.
Air is passed through the solution to oxidize $Na_2S$ to $Na_2SO_4$,preventing the reverse reaction.
Finally,$Zn$ is added to the solution to displace silver from the complex: $2Na[Ag(CN)_2] + Zn \longrightarrow Na_2[Zn(CN)_4] + 2Ag \downarrow$.
$Na_2S_2O_3$ is not used in this process.

(A) Nickel oxide $(NiO)$ is reduced by water gas $(CO + H_2)$ to obtain the metal. The other oxides are reduced by different reducing agents as shown below:
$ZnO + C \xrightarrow{\Delta} Zn + CO$
$WO_3 + 3H_2 \xrightarrow{\Delta} W + 3H_2O$
$Fe_2O_3 + 3CO \xrightarrow{\Delta} 2Fe + 3CO_2$
$2NiO + \underbrace{CO + H_2}_{\text{Water gas}} \longrightarrow 2Ni + CO_2 + H_2O$

(A) The thermite reaction involves the reduction of ferric oxide $(Fe_2O_3)$ by aluminium $(Al)$ powder.
The balanced chemical equation is:
$Fe_2O_3 + 2Al \rightarrow 2Fe + Al_2O_3$
From the stoichiometry of the reaction,$1$ mole of $Fe_2O_3$ reacts with $2$ moles of $Al$.
However,the question refers to the mass ratio or parts by weight commonly used in the thermite process.
In the standard thermite mixture,$3$ parts of ferric oxide $(Fe_2O_3)$ are mixed with $1$ part of aluminium powder $(Al)$ by weight.
Therefore,$X = 3$ and $Y = 1$.

(A) Bauxite powder reacts with coke and nitrogen as follows:
$Al_2O_3 + 3C + N_2 \xrightarrow{2075 \ K} 2AlN (X) + 3CO$
When $AlN$ reacts with water,it undergoes hydrolysis:
$AlN + 3H_2O \longrightarrow Al(OH)_3 + NH_3 \uparrow$
Thus,the gas formed is ammonia $(NH_3)$.

(D) $Ni$ anode is used in the electrolytic extraction of $Na$ by Castner's process. In this process,molten $NaOH$ is electrolyzed using a $Ni$ anode and an iron cathode.

(A) In Down's process,metallic sodium is extracted by the electrolysis of a fused mixture of $NaCl$,$CaCl_2$,and $KF$.
The addition of $CaCl_2$ and $KF$ lowers the melting point of $NaCl$ from $801^{\circ}C$ to approximately $600^{\circ}C$,which helps in reducing energy consumption and prevents the vaporization of sodium metal.
Therefore,the electrolyte used is a mixture of $NaCl$,$CaCl_2$,and $KF$.

(A) The Ellingham diagram is a graphical representation of the variation of the change in standard Gibbs free energy $(\Delta G^{\circ})$ with temperature $(T)$.
Thus,$X = \Delta G^{\circ}$ and $Y = T$.

(C) The given reaction is a classic example of the Thermite process,which is used for the reduction of metal oxides using aluminum as a reducing agent.
In the Thermite process,aluminum reduces metal oxides like $Fe_{2}O_{3}$ to produce the metal and aluminum oxide $(Al_{2}O_{3})$.
The reaction is: $Fe_{2}O_{3(s)} + 2 Al_{(s)} \xrightarrow{\text{Heat}} Al_{2}O_{3(s)} + 2 Fe_{(s)}$.
Comparing this with the given equation $M_{2}O_{3} + 2 Al \rightarrow Al_{2}O_{3} + 2 M$,we can identify that $M$ is Iron $(Fe)$.

(A) In the extraction of gold,the metal is leached with a dilute solution of $NaCN$ in the presence of air (oxygen) to form the complex $X = [Au(CN)_2]^-$.
Then,gold is recovered by displacement with zinc,which forms the complex $Y = [Zn(CN)_4]^{2-}$.
The chemical equations are:
$4Au + 8CN^- + 2H_2O + O_2 \rightarrow 4[Au(CN)_2]^- + 4OH^-$
$2[Au(CN)_2]^- + Zn \rightarrow [Zn(CN)_4]^{2-} + 2Au$
Thus,$X$ is $[Au(CN)_2]^-$ and $Y$ is $[Zn(CN)_4]^{2-}$.

(B) The given reactions represent the self-reduction (auto-reduction) process.
This process is used for the extraction of less reactive metals like $Cu$,$Hg$,and $Pb$ from their sulfide ores.
In the case of copper,the reactions are:
$2Cu_2S + 3O_2 \rightarrow 2Cu_2O + 2SO_2$
$Cu_2S + 2Cu_2O \rightarrow 6Cu + SO_2$
Therefore,the metal $M$ is $Cu$.

(C) 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,it is dissolved in molten cryolite $(Na_3AlF_6)$.
Fluorspar $(CaF_2)$ is added in small quantities to the mixture to lower the melting point of the electrolyte and to increase its electrical conductivity.
Therefore,both $(b)$ and $(c)$ are correct roles of fluorspar.

(A) Roasted copper pyrite on smelting with sand produces $FeSiO_{3}$ as fusible slag and $Cu_{2}S$ as matte.
For removing the gangue,silica $(SiO_{2})$ is added as a flux to react with iron oxide $(FeO)$ formed during the roasting process to form iron silicate $(FeSiO_{3})$ slag.
The chemical reactions are:
$2FeS + 3O_{2} \longrightarrow 2FeO + 2SO_{2}$
$FeO + SiO_{2} \longrightarrow FeSiO_{3}$
Copper matte mainly consists of a mixture of $Cu_{2}S$ and $FeS$.

(A) The melting point of pure $CaCl_{2}$ is very high $(1045 \ K)$.
Adding $CaF_{2}$ to the electrolyte mixture lowers the melting point of the electrolyte.
This allows the electrolysis process to be carried out at a lower temperature,which saves energy and prevents the evaporation of the electrolyte.