Animated Solution for Chemistry - s and p-Block Elements: In context with the industrial preparation of hydrogen from water gas ($\text{CO}+{\text{H}}_2$), which of the following is the correct statement ?

Imagine you are an industrial chemist tasked with producing massive quantities of pure hydrogen gas. One of the most common starting materials you have is water gas, which is a mixture of carbon monoxide ($\text{CO}$) and hydrogen (${\text{H}}_2$).

Your primary objective is to separate the hydrogen from the carbon monoxide. At first glance, you might think about physical separation methods like fractional distillation. However, both $\text{CO}$ and ${\text{H}}_2$ have extremely low boiling points. Cooling these gases down to liquid form to separate them would require a colossal amount of energy, making the process economically unviable. We need a smarter, chemical approach.

Instead of fighting the physical properties of the gases, chemists use a brilliant workaround known as the water-gas shift reaction (often part of the Bosch process). The trick is to transform the hard-to-remove carbon monoxide into a gas that is much easier to separate.

We introduce steam (${\text{H}}_2\text{O}$) into the water gas mixture and pass it over a catalyst—typically iron oxide promoted with chromium oxide (${\text{Fe}}_2{\text{O}}_3/{\text{Cr}}_2{\text{O}}_3$)—at a high temperature of about $673\text{ K}$.

This reaction is a double win! Not only does it consume the problematic carbon monoxide, but it also produces an additional molecule of hydrogen gas.

After the shift reaction, our gas mixture consists of carbon dioxide (${\text{CO}}_2$) and a large amount of hydrogen (${\text{H}}_2$). Now, the separation is straightforward.

Carbon dioxide is an acidic gas, whereas hydrogen is neutral. By passing this gaseous mixture through an alkaline solution, such as potassium hydroxide ($\text{KOH}$) or sodium hydroxide ($\text{NaOH}$), the carbon dioxide undergoes an acid-base neutralization reaction.

The alkali completely absorbs the ${\text{CO}}_2$, trapping it in the aqueous solution as a carbonate salt. The hydrogen gas, being unaffected by the alkali, bubbles through and is collected in a highly pure state.

This elegant sequence of oxidizing $\text{CO}$ to ${\text{CO}}_2$ with steam, followed by the absorption of ${\text{CO}}_2$ in alkali, perfectly matches the industrial reality and confirms our correct option.