Reduction to free Metal Questions in English

(D) The reduction of metal oxides by carbon depends on the thermodynamic stability of the oxides and the affinity of the metal for oxygen compared to carbon.
Metals like $Ca$ and $K$ are highly reactive and form very stable oxides ($CaO$ and $K_2O$).
The Gibbs free energy of formation for these oxides is highly negative,making them difficult to reduce using carbon at standard metallurgical temperatures.
In contrast,oxides of less reactive metals like $Fe$,$Pb$,$Cu$,and $Sn$ can be reduced by carbon because their oxides are less stable than $CO$ or $CO_2$ at higher temperatures.
Therefore,$CaO$ and $K_2O$ cannot be reduced by carbon.

(C) The extraction of aluminum is carried out by the Hall-Heroult process. In this process,pure $Al_2O_3$ (alumina) is dissolved in molten cryolite $(Na_3AlF_6)$ or fluorspar $(CaF_2)$. This mixture lowers the melting point of the electrolyte and increases its electrical conductivity. Therefore,the electrolyte used is a mixture of alumina with molten cryolite.

(B) In the blast furnace,hematite $(Fe_2O_3)$ is reduced to iron. The ore often contains silica $(SiO_2)$ as an impurity (gangue).
To remove this acidic impurity,limestone $(CaCO_3)$ is added as a flux.
At high temperatures,limestone decomposes to form calcium oxide $(CaO)$,which acts as a basic flux:
$CaCO_3 \rightarrow CaO + CO_2$
Then,$CaO$ reacts with the silica impurity to form calcium silicate slag $(CaSiO_3)$:
$CaO + SiO_2 \rightarrow CaSiO_3$
Thus,the correct flux used is limestone.

(C) Blister copper is obtained from the Bessemer converter during the extraction of copper. It contains about $98\%$ pure copper and $2\%$ impurities,which are mainly due to the evolution of $SO_2$ gas that creates blisters on the surface of the solidified metal. Therefore,the correct option is $C$.

(B) Limestone $(CaCO_3)$ acts as a basic flux to remove acidic impurities like silica $(SiO_2)$.
The reaction is: $CaO + SiO_2 \rightarrow CaSiO_3$ (slag).

(D) In the Hall-Heroult process for the extraction of aluminum,pure alumina $(Al_2O_3)$ has a very high melting point $(2323 \ K)$ and is a poor conductor of electricity.
To overcome these issues,molten cryolite $(Na_3AlF_6)$ is added to the electrolyte.
This serves two main purposes:
$1$. It lowers the melting point of the mixture to about $1240 \ K$.
$2$. It increases the electrical conductivity of the melt,facilitating the electrolytic process.

(D) The Goldschmidt thermite process involves the reduction of metal oxides (usually $Fe_2O_3$) using aluminum powder as the reducing agent.
The chemical reaction is: $Fe_2O_3(s) + 2Al(s) \rightarrow 2Fe(l) + Al_2O_3(s) + \text{Heat}$.
Here,$Al$ reduces $Fe_2O_3$ to $Fe$ and gets oxidized to $Al_2O_3$. Thus,$Al$ is the reducing agent.

(D) Steel is an alloy of iron and carbon,where the carbon content typically ranges from $0.15\%$ to $1.5\%$.
Cast iron,on the other hand,contains a higher percentage of carbon,usually between $2.2\%$ and $4.5\%$.
Therefore,the correct range for steel is $0.15 - 1.5\%$.

(C) In the $Hall-Heroult$ process,pure $Al_2O_3$ is mixed with $Na_3AlF_6$ (cryolite) and $CaF_2$ (fluorspar).
This mixture lowers the melting point of the electrolyte and increases its electrical conductivity.
Therefore,the correct mixture used as an electrolyte is molten $Al_2O_3 + Na_3AlF_6$ (often with $CaF_2$ added).

(B) $SiO_2$ is an acidic impurity. To remove acidic impurities,a basic flux is required. $CaO$ acts as a basic flux and reacts with $SiO_2$ to form slag $(CaSiO_3)$. The reaction is: $CaO + SiO_2 \rightarrow CaSiO_3$.

(D) The reduction of metal oxides with aluminum powder is known as the $Aluminothermic$ $process$ or $Goldschmidt$ $process$.
The chemical reaction is: $Cr_2O_3 + 2Al \rightarrow 2Cr + Al_2O_3 + \text{Heat}$.
This reaction is highly exothermic.

(B) The extraction of silver from its ore $(Ag_2S)$ involves the following steps:
$1$. Leaching: $Ag_2S + 4NaCN \rightarrow 2Na[Ag(CN)_2] + Na_2S$. Here,$A$ is $Na[Ag(CN)_2]$.
$2$. Displacement: $2Na[Ag(CN)_2] + Zn \rightarrow Na_2[Zn(CN)_4] + 2Ag$. Here,$B$ is $Ag$ (silver metal).
Therefore,$A = Na[Ag(CN)_2]$ and $B = Ag$.

(A) Smelting is a process of reduction of a metal oxide with carbon or other reducing agents at high temperatures,where the metal is obtained in the molten state.
Roasting and calcination are processes used to convert ores into metal oxides.
Froth flotation is a concentration method for sulfide ores.

(B) During the extraction of copper from copper pyrites $(CuFeS_2)$,the ore is roasted to remove sulfur and convert iron into iron$(II)$ oxide $(FeO)$.
$2CuFeS_2 + 4O_2 \rightarrow Cu_2S + 2FeO + 3SO_2$
Silica $(SiO_2)$ is added as a flux to remove the $FeO$ impurity as slag.
$FeO + SiO_2 \rightarrow FeSiO_3$ (slag)
Therefore,the slag is mainly composed of $FeSiO_3$.

(A) The extraction of aluminum is carried out by the Hall-$H$éroult process.
In this process,pure alumina $(Al_2O_3)$ is dissolved in molten cryolite $(Na_3AlF_6)$ and fluorspar $(CaF_2)$,which lowers the melting point of the mixture and increases its electrical conductivity.
Therefore,$Al_2O_3$ is the compound used for the extraction of aluminum by electrolysis.

(D) Wrought iron is the purest form of commercial iron,containing about $99.5 \%$ to $99.9 \%$ iron.
Because it has the lowest carbon content (less than $0.25 \%$),it has the highest melting point among the given forms of iron,typically around $1500 \ ^\circ C$ to $1550 \ ^\circ C$.

(B) Smelting is a process of reduction in which the metal oxide is reduced to the metal using a reducing agent like $C$ or $CO$.
$Fe_2O_3 + 3C \rightarrow 2Fe + 3CO$
$Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2$

(A) For low-grade copper ores,hydrometallurgy is used. The ore is leached with acid or bacteria,and then the copper is recovered by treating the solution with scrap iron or $H_2$ gas. This process involves metal displacement where $Cu^{2+}$ ions are displaced by $Fe$ atoms: $Cu^{2+}(aq) + Fe(s) \rightarrow Cu(s) + Fe^{2+}(aq)$.

(D) Smelting is a process of reduction of a metal oxide with carbon at high temperatures. $Aluminium$ cannot be extracted by smelting because it has a very high affinity for oxygen. The reduction of $Al_2O_3$ by carbon is not thermodynamically feasible at temperatures achievable in a blast furnace. Therefore,$Aluminium$ is extracted by the electrolytic reduction of fused alumina $(Al_2O_3)$ in the presence of cryolite $(Na_3AlF_6)$.

(C) In the extraction of copper from copper pyrites $(CuFeS_2)$,the concentrated ore is subjected to roasting in a reverberatory furnace to remove moisture and volatile impurities. After roasting,the ore is mixed with silica $(SiO_2)$ and coke and subjected to smelting. During smelting,iron oxide $(FeO)$ reacts with silica to form iron silicate slag $(FeSiO_3)$,while copper remains as a mixture of $Cu_2S$ and $FeS$,which is known as copper matte.

(A) In the extraction of iron from its ore,limestone $(CaCO_3)$ is added as a flux.
It decomposes to form calcium oxide $(CaO)$,which reacts with the silica $(SiO_2)$ impurity present in the ore to form calcium silicate $(CaSiO_3)$,which is known as slag.
The reaction is: $CaO + SiO_2 \rightarrow CaSiO_3$ (Slag).

(A) flux is a substance added to the ore to remove gangue by forming an easily fusible slag.
Basic fluxes are used to remove acidic impurities (like $SiO_2$).
$Silica$ $(SiO_2)$ is an acidic flux,whereas $Limestone$ $(CaCO_3)$,$Calcite$ $(CaCO_3)$,and $Quick lime$ $(CaO)$ are basic fluxes.
Therefore,$Silica$ is not a basic flux.

(A) During the Bessemer conversion process in the extraction of copper,the molten matte ($Cu_2S$ and $FeS$) is subjected to a blast of air.
First,$FeS$ is oxidized to $FeO$,which reacts with silica $(SiO_2)$ to form slag.
Then,the remaining $Cu_2S$ is partially oxidized to $Cu_2O$.
Finally,the $Cu_2S$ reacts with the formed $Cu_2O$ to produce metallic copper,a process known as self-reduction:
$Cu_2S + 2Cu_2O \rightarrow 6Cu + SO_2$.

(A) In the process of smelting,a substance called $Flux$ is added to the ore to remove impurities known as $Gangue$. The $Flux$ reacts with the $Gangue$ to form a fusible material called $Slag$. Therefore,the molten product formed by the combination of flux and impurities is known as $Slag$.

(C) Aluminum is a highly reactive metal and cannot be reduced by carbon because it has a high affinity for oxygen. Therefore,it is extracted from its ore (alumina,$Al_2O_3$) by the process of electrolytic reduction (Hall-$H$éroult process). In this process,molten $Al_2O_3$ mixed with cryolite $(Na_3AlF_6)$ and fluorspar $(CaF_2)$ is electrolyzed.

(B) In a blast furnace,the temperature varies at different heights.
The zone of combustion (or tuyere zone) is where the blast of hot air enters,resulting in the highest temperature,which is approximately $2000 \ K$ to $2200 \ K$.
Therefore,the maximum temperature is in the zone of combustion.

(A) The reaction between $Cu_2S$ and $Cu_2O$ is known as self-reduction or auto-reduction. The chemical equation is: $2Cu_2O + Cu_2S \rightarrow 6Cu + SO_2$. This process is carried out in a reverberatory furnace to extract copper metal.

(B) During the extraction of metals like $Cu$ or $Fe$,a flux is added to remove gangue impurities. The flux reacts with the gangue to form a fusible substance called slag. $Slag$ is lighter than the molten metal and floats on top,which allows it to be easily separated. Furthermore,the slag is designed to have a lower melting point than the metal to ensure it remains in a molten state during the process.

(A) Aluminum is a highly reactive metal,and its oxide $(Al_2O_3)$ is very stable.
Carbon reduction is not feasible because the temperature required is extremely high.
Therefore,the extraction is carried out by the electrolytic reduction of $Al_2O_3$ dissolved in molten cryolite $(Na_3AlF_6)$ and fluorspar $(CaF_2)$,which lowers the melting point and increases conductivity.

(D) $Smelting$ is a process of reduction of a metal oxide ore with carbon (coke) at high temperatures,where the metal is obtained in a molten state. Therefore,the ore is heated to a high temperature to melt it.

(C) In the metallurgy of copper,the molten matte is charged into a Bessemer converter.
During this process,the remaining $FeS$ is oxidized to $FeO$,which forms slag with silica $(SiO_2)$.
Finally,$Cu_2S$ is oxidized to metallic copper.
As the molten copper is poured and cooled,the dissolved $SO_2$ gas escapes,creating bubbles on the surface of the solidified copper.
This gives the copper a blistered appearance,hence it is called $Blister \ copper$.

(A) $Al_2O_3$ is a poor conductor of electricity and has a very high melting point. $Na_3AlF_6$ (cryolite) is added to lower the melting point of the mixture and increase its electrical conductivity,making the electrolysis process more efficient.

(D) In the blast furnace,the reduction of iron oxides $(Fe_2O_3)$ occurs primarily through $CO$.
While coke $(C)$ is used as a fuel and also acts as a reducing agent,$CO$ is the primary reducing agent that reacts with the iron ore at various temperature zones.
Specifically,$Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2$ is the dominant reduction reaction.

(C) Smelting is a process of reduction of a metal oxide with carbon or carbon monoxide at high temperatures.
In the extraction of iron from hematite $(Fe_2O_3)$,the ore is reduced by carbon monoxide $(CO)$ in a blast furnace.
The reaction is: $Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2$.
Option $A$ represents roasting,option $B$ represents calcination,and option $D$ represents the thermite process.

(C) The thermite process involves the reduction of metal oxides by aluminum $(Al)$ to produce the metal and aluminum oxide $(Al_2O_3)$.
This is a highly exothermic reaction used for welding.
In the reaction $2Fe + Al_2O_3 \rightarrow 2Al + Fe_2O_3$,aluminum is being oxidized and iron is being reduced,which is the reverse of the thermite process.
Since $Al$ is a stronger reducing agent than $Fe$,$Al$ can reduce $Fe_2O_3$ to $Fe$,but $Fe$ cannot reduce $Al_2O_3$ to $Al$ under standard conditions.

(D) Blister copper is the product obtained after the Bessemerization process in the extraction of copper.
It contains approximately $98\%$ pure copper and $2\%$ impurities,which are primarily due to the evolution of $SO_2$ gas that creates blisters on the surface of the solidified copper.
Therefore,it is referred to as copper with $2\%$ impurity.

(C) In the Hall-$H$éroult process,pure $Al_2O_3$ is mixed with $Na_3AlF_6$ (cryolite) or $CaF_2$ (fluorspar).
This mixture lowers the melting point of the electrolyte and increases its electrical conductivity,making the process more efficient.

(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 $Blast \ furnace$.

(D) Flux is a substance added to the furnace to remove undesirable impurities (gangue) from the ore. $Flux + \text{Gangue} ightarrow \text{Slag}$. It is commonly used to remove silica $(SiO_2)$ or undesirable metal oxides.

(C) In the Hall-Heroult process,pure $Al_2O_3$ is mixed with cryolite $(Na_3AlF_6)$ and fluorspar $(CaF_2)$.
$Na_3AlF_6$ lowers the melting point of the mixture and increases its electrical conductivity.
$CaF_2$ also helps in lowering the melting point and makes the molten mixture more fluid.

(B) In a blast furnace,the combustion zone (hearth) is the hottest part where coke burns in the presence of hot air to produce $CO_2$ and heat. This reaction is highly exothermic,which maintains the high temperature of the hearth. This zone is known as the oxidizing zone.

(D) Self-reduction (also known as auto-reduction) is typically used for metals with low electropositivity,such as $Hg$,$Cu$,and $Pb$.
$1. \text{ For } Hg: 2HgS + 3O_2$ $\rightarrow 2HgO + 2SO_2; 2HgO + HgS$ $\rightarrow 3Hg + SO_2$
$2. \text{ For } Cu: 2Cu_2S + 3O_2$ $\rightarrow 2Cu_2O + 2SO_2; 2Cu_2O + Cu_2S$ $\rightarrow 6Cu + SO_2$
$3. \text{ For } Pb: 2PbS + 3O_2$ $\rightarrow 2PbO + 2SO_2; 2PbO + PbS$ $\rightarrow 3Pb + SO_2$
$Fe$ (Iron) is a more electropositive metal and is extracted by reduction with carbon (smelting) in a blast furnace,not by self-reduction.

(B) Hydrometallurgy is a technique for the recovery of metals from ores using aqueous solutions. $Ag$ (Silver) and $Au$ (Gold) are commonly extracted using this method. In the process,the metal is leached with a suitable reagent like $NaCN$ or $KCN$ in the presence of air $(O_2)$,followed by displacement with a more reactive metal like $Zn$.

(A) The blast furnace is primarily used for the reduction of oxide ores (such as iron oxides) to their metallic form using carbon monoxide as a reducing agent.

(D) Metallurgy is the scientific and technological process of extracting metals from their ores and preparing them for use. It involves various steps such as concentration of ore,isolation of the metal from its concentrated ore,and purification of the metal.

(B) During the process of smelting,a substance called flux is added to the ore. The function of flux is to react with the non-fusible impurities (gangue) present in the ore to form a fusible substance known as slag. This slag can then be easily removed from the molten metal. Therefore,the primary function of flux is to remove the gangue.

(A) Copper matte is obtained during the extraction of copper from copper pyrites $(CuFeS_2)$.
It is a molten mixture consisting mainly of cuprous sulphide $(Cu_2S)$ and ferrous sulphide $(FeS)$.

(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 the electrolytic mixture for two main reasons:
$1$. It lowers the melting point of the mixture to about $1140 \ K$.
$2$. It increases the electrical conductivity of the molten mass.
Among the given options,the most fundamental purpose for which cryolite is added is to lower the melting point of alumina to make the process energy-efficient and feasible.

(D) The thermite process is a pyrometallurgical technique used to reduce metal oxides to their respective metals using aluminum as a reducing agent.
In this process,a mixture of metal oxide (typically $Fe_2O_3$) and aluminum powder $(Al)$ is ignited.
The reaction is highly exothermic: $Fe_2O_3(s) + 2Al(s) \rightarrow 2Fe(l) + Al_2O_3(s) + \text{Heat}$.
Therefore,the correct mixture is $Al$ powder and metal oxide.