Metallurgy

Step 1: Group 1 cyanide (NaCN) is used as a depressant in froth floatation.
Step 2: Sphalerite (ZnS) often contains Galena (PbS) as an impurity.
Step 3: NaCN reacts with ZnS to form a soluble complex , preventing it from forming froth, while PbS goes to the froth.

Step 1: Ellingham diagrams are used to predict the spontaneity of the reduction of metal oxides.
Step 2: They plot the standard Gibbs free energy of formation ( ) per mole of against absolute temperature ( ).
Step 3: The relation used is , which results in a straight line ( ) where slope is .

Step 1: Understanding the Concept:
Bauxite contains impurities like , , and .
During leaching with concentrated NaOH, amphoteric and acidic substances dissolve, while basic impurities remain solid.
Step 2: Detailed Explanation:
1. Alumina ( ) is amphoteric and dissolves to form sodium aluminate.
2. and are basic oxides and do not react with NaOH; they are filtered out as red mud.
3. is an acidic oxide. It reacts with NaOH to form soluble sodium silicate ( ).

Thus, silica leaches out along with alumina.
Step 3: Final Answer:
The correct option is (A) .

Step 1: Understanding the Concept:
During the electrolytic refining of copper, the impure copper is the anode. Metals that are less basic (less electropositive) than copper do not oxidize and instead settle below the anode as "anode mud."
Step 2: Detailed Explanation:
1. More electropositive metals (like ) dissolve in the electrolyte as sulfates.
2. Less electropositive (noble) metals and certain non-metals do not dissolve and form the anode mud.
3. According to standard chemical processing (and NCERT), the common impurities recovered from anode mud in copper refining are:
- Antimony ( )
- Selenium ( )
- Tellurium ( )
- Silver ( )
- Gold ( )
- Platinum ( )
4. Lead ( ) typically forms insoluble which precipitates but is usually classified as part of the sludge/residue rather than the specific commercial impurities meant in this context. Ru is a noble metal but is not a "main" impurity typically mentioned for blister copper.
5. Thus, the count of main impurities listed in standard texts is 6 ( ).
Step 3: Final Answer:
The total number is 6.

Step 1: Understanding the Concept:
In the Hall-Heroult process, pure alumina ( ) is mixed with cryolite ( ) to facilitate electrolysis.
Step 2: Detailed Explanation:
1. Assertion (A): Alumina has a very high melting point ( ) and is a poor conductor in the solid state. Cryolite is added to lower the melting point to approximately and increase electrical conductivity. Thus, the assertion is correct.
2. Reason (R): Cryolite is . Calculating oxidation state: . The oxidation state of Al is indeed +3. Thus, the reason is also a correct statement.
3. Logical Link: The reason for adding cryolite is to act as a flux and a solvent. The fact that Al has a +3 oxidation state in it is not the explanation for why it is used in the extraction of Al from alumina.
Step 3: Final Answer:
Both statements are true individually, but the reason does not explain the assertion.

Step 1: Leaching of Bauxite: (X).
Step 2: Neutralization with (Y): (Z) .
Step 3: Hydrated alumina (Z) is then filtered and heated to give pure alumina.

Step 1: Alumina ( ) has a very high melting point (~2323 K).
Step 2: In the Hall-Heroult process, **Cryolite** ( ) and fluorspar ( ) are added.
Step 3: These lower the melting point to about 1173 K and increase the electrical conductivity of the mixture.

Step 1: Aluminium: Kaolinite is a clay mineral, a form of aluminosilicate .
Step 2: Iron: Siderite is iron carbonate .
Step 3: Copper: Malachite is a green copper carbonate hydroxide mineral .
Step 4: Zinc: Calamine is zinc carbonate .

Step 1: Mercury (a) is a low-boiling metal, so it is refined by Distillation (ii).
Step 2: Copper (b) is refined using Electrolytic Refining (iii).
Step 3: Silicon (c) (and Germanium) requires ultra-high purity for semiconductors, achieved by Zone Refining (iv).
Step 4: Nickel (d) is refined by the Mond process, which is a type of Vapour Phase Refining (i).

In the extraction of copper, when copper oxide ( ) is reduced by hydrogen gas ( ), the copper is reduced to its metallic form and water vapor is produced as a byproduct. This process produces what is referred to as reduced copper.
Blister copper, on the other hand, refers to copper that is in a nearly pure state but still contains small amounts of other elements such as sulfur, which can create small bubbles (blisters) on its surface during the smelting process.
Thus, the correct product is reduced copper, which is the result of the reduction of with .