Question

In 1899 the German chemist Ludwig Mond developed a process for purifying nickel by converting it to the volatile nickel tetracarbonyl \(\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]\) (b.p. \(=\) \(\left.42.2^{\circ} \mathrm{C}\right)\) $$ \mathrm{Ni}(s)+4 \mathrm{CO}(g) \rightleftharpoons \mathrm{Ni}(\mathrm{CO})_{4}(g) $$ (a) Describe how you can separate nickel and its solid impurities. (b) How would you recover nickel? \(\left[\Delta H_{\mathrm{f}}^{\circ}\right.\) for \(\mathrm{Ni}(\mathrm{CO})_{4}\) is \(\left.-602.9 \mathrm{kj} / \mathrm{mol} .\right]\)

Short answer

In the Mond process, Nickel reacts with Carbon monoxide to form nickel tetracarbonyl. The nickel tetracarbonyl is volatile, so it separates from the solid impurities when heated. To recover the nickel, the nickel tetracarbonyl is heated, causing it to decompose back into nickel and carbon monoxide.

Step-by-step solution

Understand Mond Process

The Mond process is a method for purifying nickel. In this process, Nickel reacts with Carbon monoxide to form nickel tetracarbonyl. The reaction is a reversible reaction, which means it can also be reversed under certain conditions. The nickel tetracarbonyl is a volatile compound, which means it easily evaporates and can be separated from other solid impurities.

Perform Separation

In the process, the impure nickel reacts with the carbon monoxide gas to form nickel tetracarbonyl. The mixture is heated and nickel tetracarbonyl gas forms and separates from the solid impurities because it is volatile. This forms the basis of the separation technique.

Recovery of Nickel

To recover nickel, the temperature is increased, nickel tetracarbonyl decomposes into nickel and carbon monoxide. The nickel obtained in this step is the pure nickel. The reaction for recovery is: \[ \mathrm{Ni}(\mathrm{CO})_{4}(g) \rightarrow \mathrm{Ni}(s) + 4 \mathrm{CO}(g) \] This phenomenon is facilitated by the fact that formation of nickel tetracarbonyl is exothermic, thus the reaction is reversed by heating.

Key concepts

Nickel Purification

Nickel purification is a process that aims to obtain pure nickel from its naturally occurring ores, which often contain various impurities. One of the key methods for achieving this purification is the Mond process. This process cleverly utilizes the properties of nickel's interaction with carbon monoxide.
The principle behind the Mond Process is to convert nickel into a compound that is easy to separate from its impurities. Nickel reacts with carbon monoxide to form nickel tetracarbonyl, a volatile compound, allowing it to separate from solid impurities. The volatile nature of this compound is critical as it forms a gas even at relatively low temperatures, making it possible to distill the nickel away from its impurities.

• The Mond Process is based on volatility differences.
• It involves the formation of a gas that can be distilled.

This method is efficient in producing high-purity nickel and was considered revolutionary at the time of its development due to its ability to purify nickel in a straightforward manner.

Nickel Tetracarbonyl

Nickel tetracarbonyl (\[\text{Ni(CO)}_4\]) is a crucial compound in the Mond process. Its unique formation is what allows for the purification of nickel. Nickel tetracarbonyl is created by the reaction of nickel with carbon monoxide gas.
This compound is notable for several reasons:

• It is volatile, meaning it can easily change from liquid to gas.
• It has a boiling point of just 42.2°C.
• Its formation is exothermic, releasing energy in the process.

These properties facilitate the separation of nickel from other materials. The volatility means that you can heat the nickel-carbon monoxide system and obtain nickel tetracarbonyl gas, leaving solid impurities behind.Once separated, further heating will decompose nickel tetracarbonyl back into solid nickel and carbon monoxide gas, retrieving the purified nickel. Understanding these properties of nickel tetracarbonyl is critical in executing the Mond process effectively.

Chemical Reactions

Chemical reactions are central to the process of nickel purification using the Mond method. The reactions involve changes in the state and composition of materials, allowing the desired separation of nickel.
During the Mond process, the key reaction is:\[\text{Ni}( ext{s}) + 4 ext{CO}( ext{g}) \rightleftharpoons \text{Ni(CO)}_4( ext{g})\]This equilibrium reaction allows nickel to transform into a more volatile state as nickel tetracarbonyl. From there, this volatile compound can be separated from impurities.The reverse reaction is just as important:\[\text{Ni(CO)}_4( ext{g}) \rightarrow \text{Ni}( ext{s}) + 4 ext{CO}( ext{g})\]By increasing the temperature, nickel tetracarbonyl decomposes back into solid nickel and carbon monoxide gas. This step allows the recovery of pure nickel from its gaseous form.

• Reactions are driven by temperature changes.
• The process relies on the characteristics of exothermicity for reversibility.
• The reversible nature is key to both forming and breaking down nickel tetracarbonyl.

Each of these reactions is a fundamental example of how chemical principles are applied to industrial processes for material purification.