Question

What is wrong with the following procedure for obtaining magnesium? $$ \begin{aligned} \mathrm{MgCO}_{3}(s) \longrightarrow & \mathrm{MgO}(s)+\mathrm{CO}_{2}(g) \\ \mathrm{MgO}(s)+\mathrm{CO}(g) \longrightarrow & \mathrm{Mg}(s)+\mathrm{CO}_{2}(g) \end{aligned} $$

Short answer

The procedure incorrectly uses \( \mathrm{CO} \) as a reducing agent to obtain \( \mathrm{Mg} \); \( \mathrm{CO} \) is not strong enough to reduce \( \mathrm{MgO} \) to \( \mathrm{Mg} \).

Step-by-step solution

Examine the Overall Reaction

Let's combine the two reactions to see the net change. The first reaction is \( \mathrm{MgCO}_{3}(s) \rightarrow \mathrm{MgO}(s) + \mathrm{CO}_{2}(g) \). The second reaction is \( \mathrm{MgO}(s) + \mathrm{CO}(g) \rightarrow \mathrm{Mg}(s) + \mathrm{CO}_{2}(g) \). Adding these reactions, we get the overall reaction: \( \mathrm{MgCO}_{3}(s) + \mathrm{CO}(g) \rightarrow \mathrm{Mg}(s) + 2\mathrm{CO}_{2}(g) \). This suggests magnesium is produced from magnesium carbonate and carbon monoxide.

Check Conservation of Mass and Atoms

In the overall reaction \( \mathrm{MgCO}_{3}(s) + \mathrm{CO}(g) \rightarrow \mathrm{Mg}(s) + 2\mathrm{CO}_{2}(g) \), the atomic species are conserved, meaning the number of each atom (Mg, C, and O) is balanced on both sides of the equation. This context doesn't indicate any errors based on conservation principles alone.

Evaluate Chemical Feasibility

Consider the reactivity and stability of the compounds involved. \( \mathrm{MgO}(s) \) is quite stable, and \( \mathrm{Mg}(s) \) is reactive, specifically in the presence of oxygen. The second reaction \( \mathrm{MgO}(s) + \mathrm{CO}(g) \rightarrow \mathrm{Mg}(s) + \mathrm{CO}_{2}(g) \) requires reducing \( \mathrm{MgO} \) to \( \mathrm{Mg} \), a process that typically requires a very strong reducing agent or electrolytic conditions. Carbon monoxide (\( \mathrm{CO} \)) is not a strong enough reducing agent to convert \( \mathrm{MgO} \) into \( \mathrm{Mg} \).

Conclusion on the Procedure's Error

The error in the procedure lies in the use of \( \mathrm{CO} \) as the reducing agent in converting \( \mathrm{MgO} \) to \( \mathrm{Mg} \). This reaction doesn't proceed under normal conditions due to the insufficient reducing power of carbon monoxide to reduce \( \mathrm{MgO} \) to magnesium metal. Therefore, a stronger reducing agent or different method is required for magnesium extraction.

Key concepts

Magnesium Extraction

Magnesium extraction is a vital industrial process because magnesium is a lightweight and strong metal used in many products, from car parts to mobile devices. The fundamental challenge in magnesium extraction is separating it from the minerals where it naturally occurs, such as magnesium carbonate (MgCO\(_3\)) and magnesium oxide (MgO). These compounds are stable, which makes the extraction challenging.

A typical extraction process would involve converting magnesium carbonate to magnesium oxide by heating (calcination) and then reducing magnesium oxide to metallic magnesium. However, the method must be carefully chosen because not all procedures are feasible or efficient. For instance, using carbon monoxide (CO) as a reducing agent is not effective in breaking down MgO to Mg under normal conditions.

Chemical Reactivity

Understanding chemical reactivity is crucial in determining whether a reaction is feasible. Reactivity refers to how easily a substance tends to undergo a chemical change. For our extraction example, magnesium oxide (MgO) is known to be very stable, meaning it does not react, or change, readily.

To extract magnesium from MgO, a reaction must transform MgO into a less stable form like Mg. In the previous exercise, carbon monoxide was not reactive enough for this task. This highlights the importance of selecting the correct reactions and agents when planning a chemical process. The reactivity of the materials involved dictates not only whether a reaction will occur but also the conditions necessary for it to proceed.

Reduction Process

The reduction process involves gaining electrons, which, in terms of metal extraction, means converting an oxidized form of a metal (like MgO) back into its elemental form. This typically requires a reducing agent, a substance that donates electrons to another compound, thus making it less oxidized, or more 'reduced'.

In typical industrial settings, more powerful reducing agents or alternative methods such as electrolysis are used to ensure that reactions yield the desired products---for instance, turning MgO into Mg. Electrolysis, although energy-intensive, involves passing an electric current to cause a reduction reaction, effectively splitting MgO into magnesium and oxygen, bypassing the need for a chemical reducing agent like CO.

• This highlights the need for energy efficiency in metal extraction processes.
• Choosing the right method depends heavily on available resources, cost considerations, and the desired purity of the extracted metal.