Animated Solution for Chemistry - s and p-Block Elements: Match List-I with List-II. $\begin{array}{ll}\text{List-I}& \text{List-II}\\ \text{A. Sodium carbonate}& \text{(i) Deacon}\\ \text{B. Titanium}& \text{(ii) Castner-Kellner}\\ \text{C. Chlorine}& \text{(iii) van-Arkel}\\ \text{D. Sodium hydroxide}& \text{(iv) Solvay}\end{array}$ Choose the correct answer form the options given below.

The world of industrial chemistry is fascinating. It's all about taking simple, abundant raw materials and transforming them into highly valuable products through clever chemical pathways. In this problem, we are tasked with matching four important chemical substances with their respective industrial manufacturing or purification processes. Let's dive deep into each of these processes and understand the beautiful chemistry behind them.

Making Washing Soda

Our first compound is Sodium carbonate ($N{a}_{2}C{O}_3$), commonly known as washing soda. The industrial marvel used to produce it is the Solvay process.

The brilliance of the Solvay process lies in its use of inexpensive raw materials: brine (sodium chloride) and limestone (calcium carbonate). The process begins by passing ammonia ($N{H}_3$) and carbon dioxide ($C{O}_2$) through water to form ammonium bicarbonate:

This ammonium bicarbonate is then reacted with a saturated solution of sodium chloride (brine). Because sodium bicarbonate ($NaHC{O}_3$) is sparingly soluble in water, it precipitates out of the solution:

Finally, the precipitated sodium bicarbonate is filtered, dried, and heated to yield our target product, sodium carbonate:

The carbon dioxide released here is cleverly recycled back into the first step, making the process highly efficient!

Purifying Titanium

Next on our list is Titanium ($Ti$). Titanium is a crucial transition metal known for its high strength-to-weight ratio and corrosion resistance. However, extracting it in its purest form is challenging. This is where the van-Arkel method comes into play.

This method is a classic example of vapor phase refining. The impure titanium is heated in an evacuated vessel with iodine ($I_2$). The titanium reacts to form a volatile covalent compound, titanium tetraiodide ($Ti{I}_4$), leaving the impurities behind:

The gaseous $Ti{I}_4$ is then passed over a white-hot tungsten filament heated to around $1700\text{ K}$. At this extreme temperature, the compound decomposes, depositing ultra-pure titanium on the filament and releasing iodine gas, which can be reused:

Producing Chlorine

Our third substance is Chlorine ($C{l}_2$). While today most chlorine is produced via the electrolysis of brine, historically, Deacon's process was a major industrial method.

Deacon's process involves the catalytic oxidation of hydrogen chloride ($HCl$) gas. The $HCl$ gas is mixed with atmospheric oxygen and passed over a catalyst, typically cupric chloride ($CuC{l}_2$), at a temperature of about $723\text{ K}$:

This reaction is an elegant way to recover valuable chlorine gas from hydrogen chloride, which is often a byproduct of other industrial chlorination reactions.

Synthesizing Caustic Soda

Finally, we have Sodium hydroxide ($NaOH$), widely known as caustic soda. The industrial production of this strong base is achieved using the Castner-Kellner cell.

This process involves the electrolysis of an aqueous solution of sodium chloride (brine). The genius of the Castner-Kellner cell is its use of a flowing mercury cathode. In a normal electrolytic cell, hydrogen gas would evolve at the cathode because water is easier to reduce than sodium ions. However, the mercury cathode has a high overpotential for hydrogen evolution. This allows the sodium ions ($N{a}^{+}$) to be reduced instead, forming a sodium amalgam with the mercury:

This amalgam is then moved to a separate chamber where it is treated with water. The sodium reacts vigorously to form sodium hydroxide and hydrogen gas, while the mercury is recovered and pumped back into the cell:

By understanding the chemistry of these processes, the matching becomes crystal clear: - Sodium carbonate is made by the Solvay process (A $\to$ iv). - Titanium is purified by the van-Arkel method (B $\to$ iii). - Chlorine is produced by Deacon's process (C $\to$ i). - Sodium hydroxide is synthesized in the Castner-Kellner cell (D $\to$ ii).

This perfectly aligns with our first option. Mastering these industrial processes is not just about memorizing names; it's about appreciating the chemical ingenuity that powers our modern world!