Animated Solution for Chemistry - Metallurgy: The metal that can be purified economically by fractional distillation method is

The Art of Boiling Away Impurities

When we extract metals from their ores, they rarely come out perfectly pure. They are often mixed with other elements, and the final step in metallurgy is refining. There are many ways to refine a metal, but one of the most elegant and straightforward methods is fractional distillation.

Imagine you have a pot of salty water. If you want pure water, you simply boil it. The water turns into steam, leaving the heavy salt behind. You then catch the steam, cool it down, and voilà—pure water! Distillation of metals works on the exact same principle. It relies entirely on the difference in boiling points between the metal you want and the impurities you don't.

In our problem, we are asked which metal among Iron (Fe), Zinc (Zn), Copper (Cu), and Nickel (Ni) can be economically purified using this method. To answer this, we need to look at their physical properties, specifically how easily they vaporize.

Let's look at the heavyweights first. Iron, Copper, and Nickel are robust transition metals with incredibly strong metallic bonds. Because of these strong bonds, it takes a massive amount of thermal energy to break their atoms apart and turn them into a gas.

For instance, Copper boils at around $2562^{\circ }\text{C}$, Nickel at $2730^{\circ }\text{C}$, and Iron at a staggering $2862^{\circ }\text{C}$. Trying to boil these metals on an industrial scale just to purify them would require an astronomical amount of energy. It would be completely uneconomical.

Zinc

Now, let's look at Zinc (Zn). Zinc is a bit of an outlier among transition metals. It has a completely filled d-orbital ($3d^{10}4s^2$). Because its d-electrons are perfectly paired and stable, they don't participate much in metallic bonding. This makes the metallic bonds in Zinc relatively weak.

As a result, Zinc has a surprisingly low boiling point of just about $907^{\circ }\text{C}$. In the world of metallurgy, this makes Zinc a volatile metal.

When crude zinc (which often contains impurities like Iron, Lead, and Cadmium) is heated in a distillation furnace, the Zinc reaches its boiling point relatively quickly. It vaporizes into a gas, leaving the stubborn, high-boiling impurities like Iron and Lead behind in the furnace. The zinc vapor is then channeled away and condensed back into a highly pure liquid, which is cast into solid blocks.

It is crucial to remember that Zinc isn't alone in this behavior. The elements directly below it in the periodic table—Cadmium (Cd) and Mercury (Hg)—also have completely filled d-orbitals and exhibit similar volatility. Mercury is so volatile it's a liquid at room temperature!

Therefore, whenever you see a question about refining by distillation, always look for the volatile trio: Zn, Cd, and Hg. They are the undisputed champions of this purification technique.