Concentration Questions in English

(C) In $Ultrafiltration$,the separation is based on the particle size of micron-sized particles present in a liquid or gas.
In $Molecular$ $sieving$,the permeability of molecular sieve membranes based on the size and shape of the molecules is employed.
In $Gravity$ $Separation$,the difference in density of particles is employed to separate components.
In $Molecular$ $attraction$,the process involves the exchange of cations and anions between molecules.

(C) Baeyer's process is used for the purification of red bauxite,which contains iron oxide $(Fe_2O_3)$ as the main impurity.
Serpeck's process is used for the purification of white bauxite,which contains silica $(SiO_2)$ as the main impurity.

(B) In Hall's process,the bauxite ore is fused with sodium carbonate $(Na_2CO_3)$ to form soluble sodium aluminate $(NaAlO_2)$.
$Al_2O_3 \cdot 2H_2O + Na_2CO_3 \to 2NaAlO_2 + CO_2 + 2H_2O$
The resulting solution is filtered and treated with $CO_2$ to precipitate aluminum hydroxide:
$2NaAlO_2 + 3H_2O + CO_2 \xrightarrow{333 \ K} 2Al(OH)_3 \downarrow + Na_2CO_3$
Finally,the aluminum hydroxide is calcined to obtain pure alumina:
$2Al(OH)_3 \xrightarrow{1473 \ K} Al_2O_3 + 3H_2O$

(D) The purification of bauxite ore (alumina) depends on the nature of the impurities present:
$(i)$ When the impurity is primarily iron oxides $(Fe_2O_3)$,Baeyer's process is used. In this process,bauxite is treated with concentrated $NaOH$ solution,which dissolves alumina but leaves iron oxide as red mud.
$(ii)$ When the impurity is primarily silica $(SiO_2)$,Serpeck's process is used. In this process,bauxite is heated with coke and nitrogen at high temperatures to form aluminum nitride $(AlN)$,while silica is removed as silicon vapor or slag.

(C) The purification of alumina is carried out by the Baeyer's process,which involves the digestion of bauxite ore with a concentrated solution of $NaOH$ at high temperature and pressure to form soluble sodium aluminate.

(A) The Froth flotation method is based on the principle that the surface of sulphide ores is preferentially wetted by oil (pine oil),while the gangue particles are wetted by water.

(B) The froth floatation process is primarily used for the concentration of sulphide ores.
In this method,the ore particles are preferentially wetted by oil (pine oil),while the gangue particles are wetted by water.
$A$ strong current of air is blown through the suspension,creating a heavy froth.
The sulphide ore particles,being wetted by the oil,attach to the air bubbles and are carried to the surface as a froth,which is then skimmed off.
The gangue particles remain in the water and settle at the bottom.

(A) Froth flotation is a method used for the concentration of sulfide ores based on the difference in wetting properties of the ore and gangue particles with water and oil.
Roasting is a metallurgical process involving heating of ore in the presence of excess air to convert it into an oxide.
Electrolysis is typically used for the refining of metals.
Bessemerization is a process used for the reduction and purification of iron or copper.

(C) The correct answer is $(C)$.
Magnetic separation is a method used for the concentration of ores where either the ore or the impurities are magnetic in nature.
Haematite $(Fe_2O_3)$ is a magnetic iron ore,and therefore,it can be concentrated using magnetic separation.

(B) In the froth floatation process,$Pine \ oil$ is added as a foaming agent to create the froth.
Additionally,collectors like $potassium \ ethyl \ xanthate$ or $amyl \ xanthate$ are added to enhance the non-wettability of the mineral particles.

(C) The froth floatation process is primarily used for the concentration of sulphide ores.
Among the given options,Cinnabar $(HgS)$ is a sulphide ore of mercury.
Therefore,it is concentrated by the froth floatation process.

(B) Cassiterite $(SnO_2)$,also known as tinstone,is an ore of tin. Since it is non-magnetic,it can be separated from magnetic impurities such as $Fe$ and $Mn$ using electromagnetic separation.

(D) Iron ore,such as $Fe_3O_4$ or $Fe_2O_3$,contains magnetic components,while the impurities (gangue) are generally non-magnetic.
Therefore,the magnetic separation method is used for the concentration of iron ore.

(A) $FeCrO_4$ (chromite) is a magnetic impurity.
Therefore,the magnetic separation method is used to remove it from the tin ore.

(C) Chemical separation or Leaching. In this process,the powdered ore is treated with a suitable reagent which can dissolve the ore but not the impurities. For $Al_2O_3 \cdot 2H_2O$ (Bauxite),it is leached with $NaOH$ solution.

(C) Sulphide ores are generally concentrated by the froth floatation process. Since copper pyrites $(CuFeS_2)$ is a sulphide ore,it is concentrated by this method.

(B) Magnetic separation is used when either the ore or the impurities are magnetic in nature.
Magnetite $(Fe_3O_4)$ is magnetic and can be separated from non-magnetic impurities using a magnetic separator.
Similarly,in tin ores,the impurity $FeWO_4$ (wolframite,which is magnetic) is separated from the non-magnetic tin ore $SnO_2$ (cassiterite) using this method.

(D) The froth-floatation method is based on the principle of differential wettability of the ore and gangue particles by water and oil.
In this process,the ore particles are preferentially wetted by the oil (collectors like pine oil),while the gangue (impurities) particles are preferentially wetted by water.
Therefore,the pure ore is not as easily wetted by water as by pine oil,cresylic acid,etc.,which allows it to be carried to the surface in the froth.

(A) The correct answer is $A$. Zinc blende $(ZnS)$ is a sulphide ore.
Sulphide ores are typically concentrated by the $Froth \ floatation$ method,which utilizes the difference in the wetting properties of the ore and the gangue particles with oil and water.

(A) The correct answer is $(A)$.
Froth-flotation is a process specifically used for the concentration of sulphide ores.
Galena $(PbS)$ is a sulphide ore.
Cassiterite $(SnO_2)$ is an oxide ore.
Magnetite $(Fe_3O_4)$ is an oxide ore.
Malachite $(Cu(OH)_2 \cdot CuCO_3)$ is a carbonate ore.
Therefore,only Galena is concentrated by the froth-flotation method,which relies on the preferential wetting of sulphide particles by oil (frothing agent) and gangue particles by water.

(A) In metallurgy,the substance added to remove the gangue (infusible impurities) is called a flux.
The reaction is: $\text{Gangue (Infusible)} + \text{Flux} \to \text{Slag (Fusible)}$.
Therefore,the substance that reacts with gangue to form a fusible material is known as a flux.

(C) Flux is a substance added during the extraction of metals to remove impurities.
It combines with the infusible gangue present in the ore to form a fusible mass known as slag.
$Flux + Gangue \to Slag$

(A) The froth flotation process is primarily used for the concentration of sulphide ores.
$A$ Chalcopyrite $(CuFeS_2)$ is a sulphide ore,which is why it is concentrated by the froth flotation process.

(A) The correct option is $(A)$.
Ore dressing,also known as concentration or beneficiation,is the process of removing unwanted earthy or siliceous impurities (gangue) from the ore before further extraction.

(B) Wolframite ore $[FeWO_4]$ is present as an impurity in tinstone $[SnO_2]$.
Since wolframite is magnetic in nature,it is attracted by the magnetic rollers in an electromagnetic separator.
Tinstone is non-magnetic and falls away from the magnetic field,allowing for effective separation.

(D) The extraction of $Ag$ (Silver) from its ore (like $Ag_2S$) involves leaching the finely powdered ore with a dilute solution of $KCN$ in the presence of air $(O_2)$.
The chemical reaction is: $4Ag(s) + 8CN^-(aq) + 2H_2O(aq) + O_2(g) \rightarrow 4[Ag(CN)_2]^-(aq) + 4OH^-(aq)$.
The soluble complex formed is potassium argentocyanide,$K[Ag(CN)_2]$.
Thus,the element being extracted is Silver $(Ag)$.

(C) The Serpek process is used for the purification of bauxite $(Al_2O_3 \cdot 2H_2O)$ containing silica $(SiO_2)$ as an impurity.
In this process,bauxite is heated with coke and nitrogen at $1800 \ ^\circ C$ to form aluminium nitride $(AlN)$.
The silica $(SiO_2)$ is reduced by coke to silicon $(Si)$,which then volatilizes at this high temperature.
$SiO_2 + 2C \rightarrow Si + 2CO \uparrow$
Thus,coke is used to remove silicon dioxide.

(A) $(I)$ In the $Hall$ process,silica $(SiO_2)$ is removed as $SiF_4$ gas (vapor). This statement is correct.
$(II)$ The $Bayer$ process is used for bauxite containing $Fe_2O_3$ as the main impurity. This statement is correct.
$(III)$ In the $Serpeck$ process,bauxite is heated with coke and nitrogen to form $AlN$ (Aluminum Nitride). This statement is correct.
Therefore,all three statements are correct.

(C) In the Bayer's process for the extraction of aluminum from bauxite,the powdered ore is digested with a concentrated solution of $NaOH$ at $473 - 523 \ K$ and $35 - 36 \ bar$ pressure.
$Al_2O_3 \cdot 2H_2O + 2NaOH \rightarrow 2NaAlO_2 + 3H_2O$
$SiO_2 + 2NaOH \rightarrow Na_2SiO_3 + H_2O$
Here,$Al_2O_3$ (alumina) dissolves to form sodium aluminate $(NaAlO_2)$ and silica $(SiO_2)$ dissolves to form sodium silicate $(Na_2SiO_3)$.
Both are soluble in the reaction mixture.

(C) The substance added to the ore to remove impurities is called $Flux$.
The reaction is: $Flux + \text{Impurity} \rightarrow \text{Slag}$.

(B) The correct matching is as follows:
$(I)$ Magnetic separation is used for magnetic ores like chromite,$FeCr_2O_4$ $(b)$.
$(II)$ Froth flotation is used for sulphide ores like chalcocite,$Cu_2S$ $(a)$.
$(III)$ Gravity separation (levigation) is used for ores with high density compared to gangue,such as silicate ores like $Al_2(SiO_3)_3$ $(c)$.
Therefore,the correct match is $(I-b, II-a, III-c)$.

(A) The Bayer's process is used for the purification of bauxite ore $(Al_2O_3 \cdot 2H_2O)$.
In this process,the powdered bauxite ore is digested with a concentrated solution of $NaOH$ at $473-523 \ K$ and $35-36 \ \text{bar}$ pressure.
This results in the formation of soluble sodium aluminate $(NaAlO_2)$:
$Al_2O_3(s) + 2NaOH(aq) + 3H_2O(l) \rightarrow 2Na[Al(OH)_4](aq)$ or simply $Al_2O_3 + 2NaOH \rightarrow 2NaAlO_2 + H_2O$.

(B) Wolframite $(FeWO_4)$ is an impurity present in tinstone $(SnO_2)$.
Since wolframite is magnetic in nature while tinstone is non-magnetic,they are separated using the magnetic separation method.

(C) The primary ore of aluminum is bauxite $(Al_2O_3 \cdot 2H_2O)$.
Concentration of bauxite is carried out by the leaching process,specifically known as the Bayer process.
In this process,the powdered ore is treated with a concentrated solution of $NaOH$ at $473-523 \ K$ and $35-36 \ \text{bar}$ pressure to dissolve the aluminum as sodium aluminate,leaving behind impurities like $Fe_2O_3$ and $SiO_2$.

(B) In the froth flotation process,froth stabilizers are added to stabilize the froth formed. $Aniline$ and $cresol$ are commonly used as froth stabilizers.

(B) Leaching is a method of ore dressing or ore beneficiation.
It is a process used for the $Concentration$ of ores where the powdered ore is treated with a suitable solvent which dissolves the ore but not the impurities.
Therefore,leaching is a type of chemical concentration process.

(B) The froth flotation process is based on the difference in the wetting properties of the ore and the gangue particles with water and oil.
Ore particles are preferentially wetted by oil,which makes their surface hydrophobic (water-repelling).
As a result,they attach to the air bubbles and rise to the surface along with the froth.
Gangue particles are preferentially wetted by water and remain in the aqueous phase.

(A) The froth flotation method is primarily used for the concentration of sulfide ores.
Among the given options,$Galena$ $(PbS)$ is a sulfide ore.
$Cassiterite$ $(SnO_2)$ is an oxide ore,$Malachite$ $(CuCO_3 \cdot Cu(OH)_2)$ is a carbonate ore,and $Magnetite$ $(Fe_3O_4)$ is an oxide ore.
Therefore,$Galena$ is the correct answer.

(C) The extraction of alumina from bauxite is carried out by the $Bayer's$ process. $Bauxite$ $(Al_2O_3 \cdot 2H_2O)$ is treated with a concentrated solution of $NaOH$ at $473-523 \ K$ and $35-36 \ bar$ pressure. This process is a form of chemical separation known as $Leaching$,where $Al_2O_3$ dissolves to form sodium aluminate,while impurities like $SiO_2$,$Fe_2O_3$,and $TiO_2$ remain undissolved.

(B) Chromite ore $(FeO \cdot Cr_2O_3)$ is a magnetic ore.
It is concentrated by the magnetic separation method,where the powdered ore is passed over a magnetic belt to separate the magnetic ore particles from non-magnetic impurities.

(D) The $Froth \ Flotation$ method is based on the difference in the wetting properties of the ore and the gangue particles with water and oil.
In this process,the sulfide ore particles are preferentially wetted by the oil (pine oil),while the gangue particles are wetted by water.
Since the ore particles become hydrophobic (water-repelling) due to the oil coating,they attach to the air bubbles and rise to the surface as froth,while the hydrophilic gangue particles remain in the water.

(A) The process of removing unwanted siliceous,earthy,or rocky materials (gangue) from the ore is known as concentration or dressing of the ore.

(A) The $Hoopes$ process is an electrolytic refining method used for the purification of aluminum. However,the question refers to the extraction of aluminum from bauxite ore. The $Bayer$ process is used for the purification of bauxite,where bauxite ore is treated with concentrated $NaOH$ to form sodium aluminate. The $Hoopes$ process is specifically for refining aluminum metal,not for treating bauxite ore. Given the options provided,$NaOH$ (concentrated) is the reagent used in the $Bayer$ process for bauxite digestion.

(C) In the froth flotation process,a frother is required to create stable froth.
Pine oil is commonly used as a frother because it helps in forming a stable froth that carries the mineral particles to the surface.
Therefore,the correct option is $C$.

(D) Iron chromate $(FeCrO_4)$ is a magnetic ore.
Magnetic separation is a method used for the concentration of ores where either the ore or the impurities are magnetic in nature.
Since $FeCrO_4$ is magnetic,it can be separated from non-magnetic impurities using a magnetic separator.
Therefore,the correct method is magnetic separation.

(C) The froth flotation method is primarily used for the concentration of sulphide ores.
Among the given options,Cinnabar $(HgS)$ is a sulphide ore.
Horn silver is $AgCl$,Bauxite is $Al_2O_3 \cdot 2H_2O$,and Haematite is $Fe_2O_3$.
Therefore,the correct option is $C$.

(C) Cassiterite $(SnO_2)$ is a non-magnetic ore,while the impurities associated with it (such as wolframite,$FeWO_4 + MnWO_4$) are magnetic. Therefore,magnetic separation is used to remove these magnetic impurities from the non-magnetic cassiterite ore.

(C) Magnetic separation is used when either the ore or the impurities are magnetic in nature.
$Fe_3O_4$ (Magnetite) is a magnetic ore of iron $(Fe)$.
Therefore,magnetic separation is applicable for the concentration of iron ores.

(A) The froth flotation process is primarily used for the concentration of sulfide ores.
Among the given options,Galena $(PbS)$ is a sulfide ore.
Therefore,it is concentrated by the froth flotation process.