Metallurgy

The froth flotation method is a selective separation process used in mineral processing to separate hydrophobic materials from hydrophilic materials.
It is widely used for the extraction and purification of sulphide ores.
Let's examine each statement: I.
**Used for the purification of sulphide ores:** Froth flotation is indeed primarily used for concentrating sulphide ores, such as copper sulphide (CuS), zinc sulphide (ZnS), and lead sulphide (PbS), by separating them from gangue (impurities like silica, clay, etc.
).
This statement is correct.
II.
**Used for the roasting of sulphide ores:** Roasting is a pyrometallurgical process where sulphide ores are heated strongly in the presence of excess air to convert them into metal oxides or sulphates.
Froth flotation is a physical separation method based on surface properties and is used before roasting in some cases, not as the roasting process itself.
This statement is incorrect.
III.
**It is based on the relative densities of gangue and ore particles:** While gravity separation methods rely on differences in densities, froth flotation is primarily based on the differences in the wettability (hydrophobicity and hydrophilicity) of the ore and gangue particles.
This statement is incorrect.
IV.
**It is based on the wetting properties of gangue and ore particles in frothing agent and water:** In froth flotation, the ore particles are preferentially wetted by oil (or a suitable collector) and become hydrophobic, attaching to air bubbles.
The gangue particles are preferentially wetted by water and remain in the aqueous phase.
Frothing agents stabilize the froth, allowing the hydrophobic ore particles to be carried to the surface and separated.
This statement is correct.
Therefore, the correct statements regarding the froth flotation method are I and IV.

The O-H bond length in water molecules in the gas phase is well known to be approximately 95.7 pm (picometers).
Thus, the correct bond length is .

To solve this, we need to identify the metals associated with the given ores and their atomic numbers:
- Sphalerite: Sphalerite is the primary ore of zinc ( ). The atomic number of zinc is 30. Therefore, , and the atomic number of is 30.
- Malachite: Malachite is a common ore of copper ( ). The atomic number of copper is 29. Therefore, , and the atomic number of is 29.
Now, let's evaluate the options:
- Option (1): 30, 82 – Incorrect, as 82 corresponds to lead ( ), not copper.
- Option (2): 82, 30 – Incorrect, as 82 is lead ( ), not zinc, and 30 is zinc, not copper.
- Option (3): 30, 29 – Correct, as 30 is zinc ( ) and 29 is copper ( ).
- Option (4): 29, 30 – Incorrect, as 29 is copper (not the metal for sphalerite) and 30 is zinc (not the metal for malachite).
So, the atomic numbers of and are 30, 29.

Step 1: Understand the definition of each given metallurgical process.
Froth flotation: A separation technique based on the difference in the wettability of mineral and gangue particles.
Roasting: Heating an ore in the presence of air to convert it to a metallic oxide or other compound.
Hydrometallurgy: The extraction of metals from their ores using aqueous solutions.
Leaching: The process of selectively dissolving a desired mineral from an ore using a suitable reagent, while the impurities remain insoluble.
Step 2: Match the description in the question with the correct process.
The question specifically describes the selective dissolution of the ore while leaving impurities undissolved. This is the definition of leaching. Final Answer: The final answer is

Ellingham diagrams represent the temperature dependence of the stability of compounds. A metal can reduce the oxide of another metal if its line lies below the other's in the diagram. Below 1673K, Mg line lies below Al, so Mg can reduce Al\textsubscript{2}O\textsubscript{3}, not the other way around. The statement that Al reduces MgO is incorrect.

The Tyndall effect is an important property of colloidal systems. It is defined as the scattering of visible light by particles in a colloid or in very fine suspensions.

• Statement S-I: Correct. When a beam of light passes through a colloid, the light gets scattered by the dispersed particles in the colloidal solution, and this scattered light becomes visible. This is known as the Tyndall effect. Examples: sunlight scattering through mist, smoke in a dark room, etc.
• Statement S-II: Also correct. For the Tyndall effect to be observable, the particle size of the dispersed phase should be comparable to the wavelength of visible light (around 400–700 nm). If the particle size is much smaller, no significant scattering occurs, and thus, no Tyndall effect will be seen.

Both conditions are essential and valid.

Statement I: Correct. Zeolites are widely used as shape-selective catalysts due to their porous structure.
Statement II: Correct. Zeolites have a three-dimensional Al-O-Si framework with well-defined pores and cavities.
Statement III: Incorrect. Zeolites \textit{are} found in nature (e.g., volcanic rocks) and can also be synthesized artificially.
Statement IV: Correct. Zeolites (especially ZSM-5) are extensively used in petroleum refining for catalytic cracking of hydrocarbons.
Thus, the correct combination is I, II, and IV only, making option (3) correct.

Zone refining: This method is used for the purification of metals like indium (In) and gallium where impurities are swept by a molten zone. So, A → II. Liquation: In this method, a low melting metal like tin (Sn) is separated from higher melting impurities. So, B → I. Vapour phase refining: This technique refines metals like zirconium (Zr), using a volatile compound. So, C → IV. Distillation: Metals like zinc (Zn) with low boiling points are purified by distillation. So, D → III. Hence, the correct matching is: A → II, B → I, C → IV, D → III

White metal is a term that can refer to several different alloys depending on the context.
However, the most common and historically significant "white metal" alloy is **Babbitt metal**.
Babbitt metal is primarily an alloy of **tin (Sn)**, with smaller amounts of other metals like **copper (Cu)** and **antimony (Sb)**.
Lead (Pb) can also be a major component in some variations of Babbitt metal, especially cheaper grades.
Looking at the options provided:
Option (A) Li & Mg: This alloy is known for being lightweight and is used in aerospace applications, but it's not typically referred to as "white metal".

Option (B) Li & Pb: Alloys of lithium and lead are used in some specialized applications, but this is not the standard composition of "white metal".

Option (C) Pb & Sn: An alloy of lead (Pb) and tin (Sn) is a common type of white metal, particularly in the context of solders and some bearing materials (though often with antimony and copper added for strength and hardness in bearings).
This fits the description of a common "white metal" alloy.

Option (D) Pb & Al: Alloys of lead and aluminum are used in some bearing applications, but this specific binary alloy is not the primary association with the term "white metal".
Given the common usage of "white metal" to refer to lead-tin based alloys (often with other additions), option (C) is the most appropriate answer among the choices.
It's worth noting that the term "white metal" can be ambiguous and might sometimes refer to other whitish-silvery alloys.
However, in the context of common alloys, lead and tin are strongly associated with this term.

The electronegativity of group 13 elements decreases as we move down the group. B has the highest electronegativity, followed by Al, Ga, In, and Tl. Thus, the correct order is B > Al > Ga > In > Tl.

I) Mercury (Hg) is refined by distillation since it is volatile — correct.
II) Copper (Cu) is refined by poling — correct.
III) Boron (B) is purified by zone refining — correct.
IV) Titanium (Ti) is purified by Van Arkel method, not liquation — incorrect.

Let's classify the oxides one by one: - : Acidic oxide
- : Amphoteric
- : Amphoteric
- : Amphoteric
- : Neutral oxide
- : Amphoteric
- : Basic
- : Basic Amphoteric oxides: Number of amphoteric oxides = 4

Step 1: Identify ores
• Kaolinite is an ore of \textit{aluminum} (Al)
• Malachite is an ore of \textit{copper} (Cu) Step 2: Match with options
Only option (3) correctly pairs Al with kaolinite and Cu with malachite.

Hall-Heroult process: Used for the extraction of aluminum (Al).
Mond process: Used for the purification of nickel (Ni).
Van-Arkel process: Used for the purification of titanium (Ti) and zirconium (Zr).
Zone refining process: Used for the purification of indium (In), silicon (Si), germanium (Ge), and other semiconductors.

Step 1: Verifying Statement-I In the Hall-Heroult process, aluminum oxide ( ) has a high melting point (~2000 K), making electrolysis inefficient. To reduce this, cryolite ( ) is added: - Lowers the melting point to ~1000 K, making electrolysis easier. - Enhances conductivity, allowing efficient ion migration in the molten electrolyte. Thus, Statement-I is correct. Step 2: Verifying Statement-II The zone refining method is used for purification of semiconductor metals, such as silicon and germanium, not zirconium. Zirconium is purified using the van Arkel method, which involves thermal decomposition of zirconium tetraiodide ( ). Thus, Statement-II is incorrect. Conclusion Thus, the correct answer is:

In the froth flotation process, various reagents are used: 1.
Frothers (Foaming agents): These substances enhance the formation of a stable froth.
Examples include pine oil, fatty acids, eucalyptus oil.
Pine oil is a primary frother.
2.
Collectors: These enhance the non-wettability of the mineral particles and help them attach to air bubbles.
Examples include xanthates (e.
g.
, sodium ethyl xanthate) and fatty acids.
3.
Froth Stabilizers: These substances stabilize the froth, making it last longer so that the mineral can be skimmed off.
Cresols and aniline are common examples of froth stabilizers.
They reduce the surface tension of the froth bubbles to prevent them from coalescing too quickly.
4.
Depressants/Activators: Depressants prevent certain minerals from floating (e.
g.
, NaCN for ZnS in presence of PbS).
Activators enhance the floatability of a desired mineral (e.
g.
, CuSO for ZnS).
Based on this: - Xanthate: Collector.
- Aniline: Can act as a froth stabilizer.
Cresols are more commonly cited, but aniline fits the role.
- Pine oil: Frother.
- NaCN: Depressant.
Therefore, aniline is used as a froth stabilizer.
This matches option (2).

Statement-I: is amphoteric in nature.
Aluminium oxide ( ) can react with both acids and bases.
- Reaction with acid (e.
g.
, HCl): (acts as a base).
- Reaction with base (e.
g.
, NaOH): (sodium aluminate) (acts as an acid).
Since it reacts with both acids and bases, is amphoteric.
So, Statement-I is correct.
Statement-II: is more basic than .
Gallium (Ga) and Thallium (Tl) are both in Group 13.
Ga is in Period 4, Tl is in Period 6.
Down a group, metallic character generally increases, and the basicity of oxides tends to increase (while acidity decreases).
- is acidic.
- is amphoteric.
- is amphoteric (though predominantly acidic character is less than Al O , more basic).
- is basic.
- is basic.
As we go down Group 13, the oxides become more basic.
Thallium is below Gallium.
Therefore, is more basic than .
So, Statement-II is correct.
Both statements are correct.
This matches option (1).

Step 1: Industrial Preparation of Diborane Diborane ( ) is typically produced industrially by the reaction of boron trifluoride ( ) with sodium hydride ( ) at high temperatures. This reaction occurs at approximately 450 K, yielding diborane ( ) efficiently. Conclusion Thus, the correct answer is:

Zone refining is used to produce semiconductor-grade metals with high purity. The process involves the movement of a molten zone through the metal, which purifies the metal by segregating impurities.

Step 1: Electronegativity order
Correct order is , so statement-I is incorrect.
Step 2: Nature of boric acid
Boric acid is a weak monobasic acid, but it acts as a Lewis acid, not protic acid. Hence statement-II is incorrect.
Step 3: Conclusion
Both statements are incorrect.

Step 1: Verifying Statement-I In the Hall-Heroult process, aluminum oxide ( ) has a high melting point (~2000 K), making electrolysis inefficient. To reduce this, cryolite ( ) is added: - Lowers the melting point to ~1000 K, making electrolysis easier. - Enhances conductivity, allowing efficient ion migration in the molten electrolyte. Thus, Statement-I is correct. Step 2: Verifying Statement-II The zone refining method is used for purification of semiconductor metals, such as silicon and germanium, not zirconium. Zirconium is purified using the van Arkel method, which involves thermal decomposition of zirconium tetraiodide ( ). Thus, Statement-II is incorrect. Conclusion Thus, the correct answer is:

Step 1: Industrial Preparation of Diborane Diborane ( ) is typically produced industrially by the reaction of boron trifluoride ( ) with sodium hydride ( ) at high temperatures. This reaction occurs at approximately 450 K, yielding diborane ( ) efficiently. Conclusion Thus, the correct answer is:

Diborane (B H ) contains:
- Four terminal B-H bonds (2c-2e), so X = 4
- Two bridging hydrogen bonds (3c-2e), so Y = 2
Thus, X + Y = 4 + 2 = 6

In the froth flotation process, various reagents are used: 1.
Frothers (Foaming agents): These substances enhance the formation of a stable froth.
Examples include pine oil, fatty acids, eucalyptus oil.
Pine oil is a primary frother.
2.
Collectors: These enhance the non-wettability of the mineral particles and help them attach to air bubbles.
Examples include xanthates (e.
g.
, sodium ethyl xanthate) and fatty acids.
3.
Froth Stabilizers: These substances stabilize the froth, making it last longer so that the mineral can be skimmed off.
Cresols and aniline are common examples of froth stabilizers.
They reduce the surface tension of the froth bubbles to prevent them from coalescing too quickly.
4.
Depressants/Activators: Depressants prevent certain minerals from floating (e.
g.
, NaCN for ZnS in presence of PbS).
Activators enhance the floatability of a desired mineral (e.
g.
, CuSO for ZnS).
Based on this: - Xanthate: Collector.
- Aniline: Can act as a froth stabilizer.
Cresols are more commonly cited, but aniline fits the role.
- Pine oil: Frother.
- NaCN: Depressant.
Therefore, aniline is used as a froth stabilizer.
This matches option (2).

Statement-I: is amphoteric in nature.
Aluminium oxide ( ) can react with both acids and bases.
- Reaction with acid (e.
g.
, HCl): (acts as a base).
- Reaction with base (e.
g.
, NaOH): (sodium aluminate) (acts as an acid).
Since it reacts with both acids and bases, is amphoteric.
So, Statement-I is correct.
Statement-II: is more basic than .
Gallium (Ga) and Thallium (Tl) are both in Group 13.
Ga is in Period 4, Tl is in Period 6.
Down a group, metallic character generally increases, and the basicity of oxides tends to increase (while acidity decreases).
- is acidic.
- is amphoteric.
- is amphoteric (though predominantly acidic character is less than Al O , more basic).
- is basic.
- is basic.
As we go down Group 13, the oxides become more basic.
Thallium is below Gallium.
Therefore, is more basic than .
So, Statement-II is correct.
Both statements are correct.
This matches option (1).

Step 1: Understand the Leaching Process.
Leaching is a chemical concentration method used for ores where the ore is soluble in a suitable solvent, but the impurities are not. The metal is then recovered from the solution. This process is particularly effective for precious metals (like gold and silver) and for aluminum. Step 2: Analyze each metal for concentration by leaching. \begin{itemize} \item I) Ag (Silver): Silver ores (like argentite, Ag S) are concentrated by cyanide leaching (MacArthur-Forrest cyanide process). The ore is treated with a dilute solution of sodium or potassium cyanide in the presence of air (oxygen). Silver forms a soluble dicyanoargentate(I) complex. So, silver is concentrated by leaching. \item II) Au (Gold): Gold is also extracted by cyanide leaching. Gold reacts with oxygen and cyanide ions to form a soluble dicyanoaurate(I) complex. So, gold is concentrated by leaching. \item III) Zn (Zinc): Zinc ores (like sphalerite, ZnS) are primarily concentrated by froth flotation, followed by roasting. While there can be hydrometallurgical routes involving leaching for zinc, the primary and most common concentration method is froth flotation for sulfide ores. For oxide ores, sometimes acid leaching is used, but it's not typically the \textit{initial} concentration step for the ore itself in the way cyanide leaching is for Ag/Au or Bayer process for Al. Therefore, it's generally not considered among the metals \textit{primarily} concentrated by leaching in this context. \item IV) Al (Aluminum): Aluminum ore (bauxite, Al O .nH O) is concentrated by the Bayer process, which is a leaching process. Bauxite is digested with a hot concentrated solution of NaOH, which dissolves alumina to form soluble sodium meta-aluminate, while impurities like iron oxides remain insoluble. So, aluminum is concentrated by leaching. \end{itemize} Step 3: Identify the correct combination.
From the analysis, Ag (I), Au (II), and Al (IV) are metals whose ores are concentrated by leaching. Zinc (III) is generally not. Step 4: Match with the given options.
The combination I, II& IV only matches option (4).

In a blast furnace, the reduction of iron oxide takes place in stages. At temperatures above 900 K, iron(II) oxide ( ) is reduced by carbon monoxide to iron metal. This corresponds to the third reaction.

Copper matte is the product formed during the smelting of copper ores. It mainly contains copper(I) sulfide (Cu S) and iron(II) sulfide (FeS).

- Froth flotation is used for sulphide ores like sphalerite (ZnS).
- Malachite and bauxite are concentrated by other methods.