Animated Solution for Chemistry - s and p-Block Elements: Water does not produce $\text{CO}$ on reacting with

This question takes us on a fascinating journey through the industrial preparation of gases and the fundamental nature of oxides. We are asked to identify which of the given substances—methane (${\text{CH}}_4$), carbon ($\text{C}$), carbon dioxide (${\text{CO}}_2$), or propane (${\text{C}}_3{\text{H}}_8$)—does not produce carbon monoxide ($\text{CO}$) when reacted with water.

To solve this, we need to understand two distinct chemical phenomena: the high-temperature reaction of steam with hydrocarbons/carbon, and the room-temperature dissolution of acidic oxides in water.

Imagine you are in a massive chemical plant. One of the most crucial intermediate mixtures produced industrially is syngas (synthesis gas), which is a mixture of carbon monoxide and hydrogen gas. How do we make it? We strip oxygen from water using carbon or hydrocarbons at blisteringly high temperatures!

When steam (${\text{H}}_2\text{O}$) is passed over red-hot coke (pure carbon) at around $1270\text{ K}$, a highly endothermic reaction occurs:

Similarly, hydrocarbons like methane and propane can be forced to react with steam. This process, known as steam reforming, requires a nickel catalyst to break the strong $\text{C-H}$ and $\text{O-H}$ bonds:

In all these cases, the carbon atom is partially oxidized to form carbon monoxide ($\text{CO}$). Therefore, options (a), (b), and (d) all produce $\text{CO}$.

Carbon Dioxide

Now, let's look at carbon dioxide (${\text{CO}}_2$). Unlike methane or pure carbon, the carbon atom in ${\text{CO}}_2$ is already fully oxidized; it sits at its maximum oxidation state of $+4$.

When ${\text{CO}}_2$ interacts with water, it doesn't undergo a redox reaction to form $\text{CO}$. Instead, it simply hydrates. Carbon dioxide is an acidic oxide (the anhydride of carbonic acid). When it dissolves in water, it forms a weak acid:

This is the exact reaction that gives your favorite sodas their fizz and contributes to the natural acidity of rainwater. No carbon monoxide is produced in this process.

By analyzing the chemical behavior of each substance with water, it becomes crystal clear that while hydrocarbons and carbon act as reducing agents at high temperatures to strip oxygen from steam (forming $\text{CO}$), carbon dioxide merely dissolves to form carbonic acid. Thus, ${\text{CO}}_2$ is the correct answer.