Reduction to free Metal Questions in English

(C) In the electrolytic extraction of aluminum,pure alumina $(Al_2O_3)$ has a very high melting point and is a poor conductor of electricity.
Cryolite $(Na_3AlF_6)$ is added to alumina to lower its melting point and increase its electrical conductivity.

(D) Calcium is obtained by the electrolysis of a fused mixture of calcium chloride $(CaCl_2)$ with about $16 \%$ calcium fluoride $(CaF_2)$ in a graphite crucible.
$CaF_2$ is added to lower the melting point of the mixture and to increase the electrical conductivity.

(C) In the $Down's \ process$,$CaCl_2$ is added to the electrolyte $(NaCl)$ to lower the melting point of the mixture from $1075 \ K$ to approximately $850 \ K$.
This reduction in temperature helps in saving energy and prevents the volatilization of metallic sodium.

(D) $CaF_2$ is added to the mixture to lower its melting point and increase electrical conductivity.
To prevent magnesium from oxidation during the electrolytic extraction process,the entire operation is carried out in an atmosphere of coal gas.

(D) Thermite welding is based on the fact that aluminium has a great affinity for oxygen and its oxidation is a highly exothermic process. In this process,aluminium powder is used to reduce metal oxides (like $Fe_2O_3$) to their respective metals,releasing a large amount of heat.

(C) $Aluminium$ oxide $(Al_2O_3)$ has a very high negative enthalpy of formation,which makes it thermodynamically very stable.
Because of this high stability,it cannot be easily reduced by common chemical reducing agents like carbon or hydrogen.
Therefore,it is typically reduced by electrolytic reduction.

(A) The correct answer is $(A)$.
In the thermite process,aluminum $(Al)$ powder is used as a reducing agent to reduce metal oxides (like $Fe_2O_3$) to their respective metals.
The reaction is highly exothermic: $Fe_2O_3 + 2Al \rightarrow 2Fe + Al_2O_3 + \text{Heat}$.

(C) The Goldschmidt aluminothermic process uses a mixture known as thermite.
Thermite consists of a mixture of metal oxide (usually $Fe_2O_3$) and aluminum powder $(Al)$ in a ratio of $3:1$ by mass.
The chemical reaction is: $Fe_2O_3 + 2Al \rightarrow 2Fe + Al_2O_3 + \text{Heat}$.

(A) The Serpeck's process is used for the purification of bauxite ore containing silica as an impurity.
In this process,bauxite is heated with coke and nitrogen at $1800 \ ^\circ C$ to form aluminum nitride $(AlN)$.
The chemical reaction is: $Al_2O_3 + 3C + N_2 \rightarrow 2AlN + 3CO$.
The aluminum nitride $(AlN)$ formed is then hydrolyzed with water:
$AlN + 3H_2O \rightarrow Al(OH)_3 + NH_3$.
Thus,ammonia $(NH_3)$ is obtained as a by-product in this process.

(D) . Cryolite $(Na_3AlF_6)$ is added to alumina $(Al_2O_3)$ during the Hall-$H$éroult process for two main reasons:
$1$. It decreases the melting point of the mixture from approximately $2323 \ K$ to about $1140 \ K$,which saves energy.
$2$. It increases the electrical conductivity of the molten mixture,facilitating the electrolysis process.

(B) Cryolite $(Na_3AlF_6)$ is added during the electrolytic extraction of aluminium for two main reasons:
$(1)$ To decrease the melting point of the mixture from $2323 \ K$ to approximately $1140 \ K$,which saves energy.
$(2)$ To increase the electrical conductivity of the molten electrolyte.

(B) In the Hall-$H$éroult process for the extraction of aluminium,pure $Al_2O_3$ has a very high melting point (approx. $2050 \ ^\circ C$).
Adding molten cryolite $(Na_3AlF_6)$ serves two main purposes:
$1$. It significantly lowers the melting point of the mixture to about $950 \ ^\circ C$,which saves energy.
$2$. It increases the electrical conductivity of the molten mass,facilitating the electrolysis process.

(C) In the Hall-$H$éroult process for the extraction of aluminium,pure alumina $(Al_2O_3)$ is dissolved in molten cryolite $(Na_3AlF_6)$.
This mixture is used as the electrolyte because it lowers the melting point of the mixture and increases its electrical conductivity.

(B) Aluminium is obtained by the Hall-$H$éroult process,which involves the electrolysis of alumina $(Al_2O_3)$ dissolved in molten cryolite $(Na_3AlF_6)$.
The cryolite lowers the melting point of the mixture and increases its electrical conductivity.
The overall reaction is:
$2Al_2O_3 + 3C \rightarrow 4Al + 3CO_2$
At the cathode:
$Al^{3+} + 3e^- \rightarrow Al$
At the anode:
$C(s) + O^{2-} \rightarrow CO + 2e^-$
$C(s) + 2O^{2-} \rightarrow CO_2 + 4e^-$

(B) In the Hall-Heroult process,pure alumina $(Al_2O_3)$ has a very high melting point (about $2323 \ K$) and is a poor conductor of electricity.
Cryolite $(Na_3AlF_6)$ is added to alumina to lower its melting point to about $1140 \ K$ and to increase its electrical conductivity,making the electrolysis process more efficient.

(B) Fluorspar $(CaF_2)$ is added in small quantities during the electrolytic reduction of alumina $(Al_2O_3)$ dissolved in fused cryolite $(Na_3AlF_6)$.
Its primary functions are to lower the melting point of the mixture and to increase the electrical conductivity of the melt,which facilitates the electrolysis process at a lower temperature of approximately $1140 \, K$.

(D) In the Hall-Heroult process for the electrolytic production of aluminium,the electrolytic cell consists of a steel vessel lined with carbon (graphite),which acts as the cathode.
Graphite rods are suspended in the molten electrolyte,which act as the anode.
Therefore,both the cathode and the anode are made of carbon (graphite).

(C) In the commercial electrochemical process for aluminium extraction,known as the Hall-$H$éroult process,the electrolyte used is a molten mixture of $Al_2O_3$ (alumina),$Na_3AlF_6$ (cryolite),and $CaF_2$ (fluorspar).
Cryolite lowers the melting point of the mixture and increases its electrical conductivity.

(B) Cryolite $(Na_3AlF_6)$ is added to the aluminium oxide $(Al_2O_3)$ during electrolysis.
It serves two main purposes:
$1$. It lowers the melting point of the mixture from approximately $2050 \ ^\circ C$ to about $950 \ ^\circ C$.
$2$. It increases the electrical conductivity of the molten mass,thereby accelerating the process.

(C) The Hall-Heroult process involves the electrolytic reduction of alumina $(Al_2O_3)$.
Pure alumina has a very high melting point and is a poor conductor of electricity.
To overcome this,alumina is dissolved in a fused mixture of cryolite $(Na_3AlF_6)$ and fluorspar $(CaF_2)$.
This mixture serves two main purposes:
$1$. It lowers the melting point of the mixture to approximately $1240 \ K$.
$2$. It increases the electrical conductivity of the melt.
Therefore,the correct option is $C$.

(C) In the electrolytic method of obtaining aluminium from purified bauxite,cryolite $(Na_3AlF_6)$ is added to the charge because it reduces the melting point of bauxite (from $2050\ ^oC$ to approximately $900\ ^oC$) and increases the electrical conductivity of the mixture.

(B) . Pure alumina $(Al_2O_3)$ is a bad conductor of electricity and has a very high melting point of about $2000\ ^\circ C$.
At this temperature,the formed $Al$ metal vaporizes because its boiling point is $1800\ ^\circ C$.
To lower the melting point and improve conductivity,$Na_3AlF_6$ (cryolite) and $CaF_2$ (fluorspar) are added to the alumina.

(D) The extraction of lead from its principal ore,galena $(PbS)$,involves a process known as self-reduction or auto-reduction.
In the reverberatory furnace,the ore is partially roasted in air to convert some $PbS$ into $PbO$ and $PbSO_4$:
$2PbS + 3O_2 \rightarrow 2PbO + 2SO_2$
$PbS + 2O_2 \rightarrow PbSO_4$
After partial roasting,the air supply is cut off,and the temperature is raised. The remaining $PbS$ reacts with the $PbO$ and $PbSO_4$ formed to produce metallic lead:
$PbS + 2PbO \rightarrow 3Pb + SO_2$
$PbS + PbSO_4 \rightarrow 2Pb + 2SO_2$
This process is called self-reduction.

(A) Thomas slag is a byproduct of the steel industry,specifically produced during the manufacturing of steel from pig iron containing phosphorus. It is chemically known as tetracalcium phosphate,represented as $Ca_3(PO_4)_2 \cdot CaO$ or $Ca_4P_2O_9$. It is used as a fertilizer.

(B) The thermite process involves the reduction of a metal oxide by aluminum powder.
The most common thermite mixture consists of iron$(III)$ oxide $(Fe_2O_3)$ and aluminum $(Al)$ powder.
The reaction is highly exothermic: $Fe_2O_3 + 2Al \rightarrow 2Fe + Al_2O_3 + \text{Heat}$.

(C) The cyanide process (also known as the Mac-Arthur Forest process) is used in the extraction of both $Au$ (Gold) and $Ag$ (Silver).
In this process,the metal is leached with a dilute solution of $NaCN$ or $KCN$ in the presence of air (as a source of $O_2$),which acts as an oxidizing agent.
The metals form soluble complex salts with the $CN^-$ ion,such as $[Au(CN)_2]^-$ and $[Ag(CN)_2]^-$,due to the presence of a lone pair of electrons on the nitrogen atom of the cyanide ion.

(A) The ease of reduction of a metal oxide depends on the thermodynamic stability of the oxide,which is related to the standard Gibbs free energy of formation $(\Delta G_f^\circ)$.
Metals with higher negative values of $\Delta G_f^\circ$ form more stable oxides,making them harder to reduce.
According to the Ellingham diagram,alkali and alkaline earth metals like $Cs$ and $Mg$ have very stable oxides compared to transition metals like $Zn$ or $Ag$.
Among the given options,$Cs$ (Cesium) is an alkali metal with a very high affinity for oxygen,making its oxide the most stable and thus the most difficult to reduce to the metal.

(B) In the extraction of $Zn$ from its ore (usually $ZnO$),the reduction is carried out by heating with coke $(C)$.
Since $Zn$ has a low boiling point $(907 \ ^\circ C)$,it is obtained in the vapor state.
The metal is then recovered by condensation of the metal vapors.
Because the metal itself is volatile and can be separated from the non-volatile impurities by distillation,the addition of a flux to form a slag is not required.

(B) Smelting is a pyrometallurgical process used to extract a metal from its ore by heating it beyond its melting point in the presence of a reducing agent like coke or $CO$.
This process involves the reduction of metal oxides to their metallic state.
For example,in the extraction of iron:
$Fe_2O_3 + 3C \to 2Fe + 3CO$
$Fe_2O_3 + 3CO \to 2Fe + 3CO_2$

(A) Smelting is a process of reduction of a metal oxide with carbon or carbon monoxide at high temperatures.
This process is typically carried out in a $Blast \ furnace$ to extract metals like iron from their ores.

(A) During the extraction of copper from copper pyrites $(CuFeS_2)$,the ore is roasted in a reverberatory furnace. The resulting molten mass,known as copper matte,consists primarily of a mixture of cuprous sulfide $(Cu_2S)$ and ferrous sulfide $(FeS)$.

(D) An $Electric \ furnace$ can produce the highest temperature among the given options. It uses electrical energy to generate heat,which can reach temperatures exceeding $3000 \ ^\circ C$,whereas other furnaces like $Blast \ furnace$ or $Reverberatory \ furnace$ are limited by the combustion of fuels.

(D) Smelting is a process of reduction of a metal oxide ore with a reducing agent like carbon (coke) at high temperatures,often in the presence of a flux to remove impurities as slag.

(A) The process of extraction of a metal in its molten (fused) state by using a reducing agent in the presence of a flux is called $Smelting$.
For example,oxides of less electropositive metals like $Pb$,$Zn$,$Fe$,and $Cu$ are reduced by carbon or other reducing agents at high temperatures to obtain the metal in a fused state.

(B) Smelting is a process of reduction of a metal oxide with carbon at high temperatures.
In the reaction $Fe_2O_3 + 3C \to 2Fe + 3CO$,iron oxide is reduced by carbon to metallic iron,which is a characteristic smelting process.
Therefore,the correct option is $(B)$.

(A) In metallurgy,flux is a substance added to the ore to react with infusible impurities (gangue) to form a fusible material known as slag.
$Flux + \text{Gangue} \rightarrow \text{Slag}$

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

(C) In the extraction of iron,the iron ore contains acidic impurities of $SiO_2$ (silica).
To remove this,a basic flux,$CaCO_3$ (limestone),is added.
$CaCO_3$ decomposes to form $CaO$,which reacts with $SiO_2$ to form $CaSiO_3$ (slag).
$CaCO_3 \to CaO + CO_2$
$CaO + SiO_2 \to CaSiO_3$ (Slag)

(B) $CaCO_3 \to CaO + CO_2$
$\underset{\text{Flux}}{CaO} + \underset{\text{Impurity of haematite}}{SiO_2} \to \underset{\text{Slag}}{CaSiO_3}$
In the extraction of iron,limestone $(CaCO_3)$ decomposes to form calcium oxide $(CaO)$,which acts as a flux to remove acidic impurities like silica $(SiO_2)$ in the form of slag $(CaSiO_3)$.

(B) During the extraction of copper from copper pyrites $(CuFeS_2)$,the iron impurity $(FeO)$ is removed by adding silica $(SiO_2)$ as a flux.
The reaction is: $FeO (s) + SiO_2 (s) \to FeSiO_3 (l)$ (slag).
Thus,the slag formed is iron silicate $(FeSiO_3)$.

(C) The extraction of silver $(Ag)$ involves hydrometallurgy,where a complex is formed.
The chemical reactions are as follows:
$Ag_2S + 4NaCN \to 2Na[Ag(CN)_2] + Na_2S$
$2Na[Ag(CN)_2] + Zn \to Na_2[Zn(CN)_4] + 2Ag$
In this process,silver is dissolved in a sodium cyanide solution to form the soluble complex $Na[Ag(CN)_2]$.

(B) The amalgamation process involves the use of mercury $(Hg)$ to extract noble metals like silver $(Ag)$ or gold $(Au)$ from their ores.
In the extraction of silver,the ore is treated with mercury to form an amalgam,which is then distilled to recover the pure metal.
The chemical principle involves the formation of a metal-mercury alloy (amalgam) followed by distillation: $Ag + Hg \to Ag-Hg \text{ (amalgam)}$.
Therefore,silver is the metal extracted by this process.

(C) In the process of metallurgy,the flux reacts with the gangue to form a fusible substance called slag.
For example,in the extraction of iron,$CaO$ (flux) reacts with $SiO_2$ (gangue) to form $CaSiO_3$ (slag).
Thus,$CaSiO_3$ is the slag.

(B) Silica $(SiO_2)$ is an acidic impurity (gangue). To remove it,a basic flux such as calcium oxide $(CaO)$ is added to form a fusible slag,calcium silicate $(CaSiO_3)$.
$SiO_2 (\text{acidic impurity}) + CaO (\text{basic flux}) \to CaSiO_3 (\text{slag})$

(D) In metallurgy,the unwanted earthy impurities present in the ore are called $Gangue$.
To remove these impurities,a substance called $Flux$ is added.
The $Flux$ reacts with the $Gangue$ to form a fusible substance known as $Slag$.
$Flux + Gangue \rightarrow Slag$
Therefore,the correct statement is that fluxes are carefully chosen to combine with the gangue present in the ore to produce easily fusible slag to carry away the impurities.

(B) In a modern blast furnace,the charge (or burden) consists of a mixture of calcined iron ore (iron oxides),limestone $(CaCO_3)$,and coke.
$1$. The iron ore provides the source of iron.
$2$. Limestone acts as a flux to remove impurities like silica $(SiO_2)$ by forming slag $(CaSiO_3)$.
$3$. Coke acts as both a fuel and a reducing agent to reduce iron oxides to metallic iron.

(D) The blast furnace is divided into different zones based on temperature gradients. The combustion zone,located at the bottom where hot air is blasted,reaches the highest temperature of approximately $2200 \, K$ (often cited as $1800 \, K - 2200 \, K$).

Zone	Temperature
Combustion zone	$2200 \, K$
Fusion zone	$1600 \, K$
Slag zone	$1300 \, K$
Reduction zone	$800 \, K$

(D) Flux is a substance added to the ore to remove gangue (impurities) by forming a fusible material called slag.
Depending on the nature of the impurity,different types of flux are used.
If the impurity is acidic (e.g.,$SiO_2$),a basic flux (e.g.,$CaO$) is used.
If the impurity is basic (e.g.,$FeO$),an acidic flux (e.g.,$SiO_2$) is used.
Therefore,flux is used to remove both acidic and basic impurities.