Animated Solution for Chemistry - General Principles and Processes of Isolation of Metals: The correct statement is

Metallurgy is a fascinating blend of chemistry and engineering, where we transform raw, impure rocks dug from the earth into the shiny, pure metals that build our modern world. This question tests our fundamental understanding of several key metallurgical processes. Let's break down each statement to separate the facts from the fiction.

Leaching of Bauxite

Let's start with the first statement, which discusses the concentration of bauxite. Bauxite is the principal ore of aluminium, but it doesn't come out of the ground pure. It is typically contaminated with silica (), iron oxides (), and titanium dioxide ().

To purify it, we use a chemical method called leaching, specifically known as the Bayer process. The powdered ore is digested with a concentrated solution of sodium hydroxide () at a high temperature () and pressure.

Here is where the beautiful chemistry of amphoteric and acidic oxides comes into play. Aluminium oxide is amphoteric, and silica is acidic. Both of these react with the strong base, , to form soluble complexes:

On the other hand, the impurities like iron oxide and titanium dioxide are basic in nature. They refuse to react with the and remain completely insoluble. When we filter this hot mixture, these insoluble impurities are left behind as a residue commonly called 'red mud'. The filtrate that passes through contains our soluble sodium aluminate and sodium silicate.

Thus, the statement "leaching of bauxite using concentrated solution gives sodium aluminate and sodium silicate" is absolutely correct.

Now, let's quickly see why the other options fall flat.

The Hall-Heroult Process: Statement (b) claims this process is used for both aluminium and iron. This is incorrect. The Hall-Heroult process is an electrolytic reduction method used exclusively for the extraction of aluminium from purified alumina. Iron, being less reactive, is extracted via carbon reduction in a massive blast furnace.

The Iron Hierarchy: Statement (c) states that pig iron is obtained from cast iron. This is chronologically backward! Pig iron is the raw, impure iron (containing about carbon) that flows directly out of the blast furnace. We take this pig iron, melt it down with scrap iron and coke, and cool it to produce cast iron (which has a slightly lower carbon content of about ).

The Story of Blister Copper: Statement (d) attributes the blistered appearance of copper to carbon dioxide. During the final stages of copper extraction in a Bessemer converter, the copper(I) oxide reacts with copper(I) sulphide in an auto-reduction process:

As the molten copper cools and solidifies, the dissolved sulphur dioxide (

$${\text{SO}}_2$$

) gas escapes, leaving behind blister-like eruptions on the surface of the metal. It has nothing to do with .

By systematically analyzing the chemistry behind each process, we can confidently conclude that only the first statement holds true.