Question

In the metallurgical process of refining nickel, the metal is first combined with carbon monoxide to form tetracarbonylnickel, which is a gas at \(43^{\circ} \mathrm{C}\) : $$\mathrm{Ni}(s)+4 \mathrm{CO}(g) \longrightarrow \mathrm{Ni}(\mathrm{CO})_{4}(g)$$ This reaction separates nickel from other solid impurities. (a) Starting with \(86.4 \mathrm{~g}\) of \(\mathrm{Ni}\), calculate the pressure of \(\mathrm{Ni}(\mathrm{CO})_{4}\) in a container of volume \(4.00 \mathrm{~L}\). (Assume the above reaction goes to completion.) (b) On further heating the sample above \(43^{\circ} \mathrm{C}\), it is observed that the pressure of the gas increases much more rapidly than predicted based on the ideal gas equation. Explain.

Short answer

a) The pressure of Ni(CO)₄ is approximately 9.57 atm. b) The pressure increases rapidly because tetracarbonylnickel decomposes to form more gaseous molecules, and because the gases deviate from ideal behaviour at high pressures.

Step-by-step solution

Reactant to Product Conversion

Calculate the number of moles \(n\) of Ni used in the reaction using its molar mass. As \(n = \frac{mass}{molar~mass}\), and the molar mass of Ni is approximately \(58.69 \mathrm{g/mol}\), so \(n = \frac{86.4g}{58.69g/mol} = 1.47 mol\). In the reaction, 1 mol of Ni forms 1 mol of Ni(CO)₄. Hence, \(1.47 mol\) of Ni forms \(1.47 mol\) of Ni(CO)₄.

Calculate Pressure of Ni(CO)₄

The pressure \(P\) of the Ni(CO)₄ can be calculated using the ideal gas equation \(PV=nRT\), where \(R = 0.0821 L·atm/mol·K\) and temperature \(T = 43^{\circ} \mathrm{C} = 273 + 43 = 316K\). Rearranging for \(P\), we get \(P = \frac{nRT}{V}\) = \(\frac{1.47 * 0.0821 * 316}{4.00}\) ≈ 9.57 atm.

Explain Deviation

At temperatures above \(43^{\circ} \mathrm{C}\), pressure increases rapidly due to the breakdown of tetracarbonylnickel into nickel and carbon monoxide, thus increasing the number of gas molecules beyond what is expected for an ideal gas behaving according to \(PV=nRT\). Additionally, at higher pressures, the gases no longer behave ideally due to factors such as intermolecular interactions and the non-zero volumes of gas particles.

Key concepts

Nickel Refining

Nickel refining is a fascinating and complex metallurgical process. It all begins with raw nickel, which isn't pure by nature. To refine nickel, it is subjected to various processes that extract it from ore and separate it from impurities. One key method involves transforming nickel into a more volatile compound that can be easily separated.

In one of these processes, nickel is mixed with carbon monoxide to form tetracarbonylnickel ( Ni(CO)_4 ). This compound is gaseous at relatively low temperatures, specifically at about 43°C.

This phase change allows for the pure nickel to be isolated from its impurities, as the gaseous form is easier to handle and transport. Once isolated, the compound can be further treated to release the pure nickel, completing the refining process. This method, known as the "Mond Process," exploits the unique properties of tetracarbonylnickel to achieve high-purity nickel.

Ideal Gas Law

The Ideal Gas Law is a fundamental equation in chemistry, represented as PV=nRT. It describes the relationship between pressure (P), volume (V), and temperature (T) of a gas, with n being the number of moles of the gas, and R representing the ideal gas constant.

This law simplifies calculations for gases under ideal conditions—when the gas particles are assumed to have no volume and no interactions with each other. It is used in the nickel refining process to predict the behavior of gaseous tetracarbonylnickel.

• P: Pressure of the gas
• V: Volume of the container
• T: Temperature, converted into Kelvin
• n: Moles of gas
• R: Ideal gas constant (0.0821 L·atm/mol·K)

For instance, in a scenario where the volume and temperature are known, and the number of moles is calculated, the Ideal Gas Law can determine the pressure exerted by the gas. However, real gases may deviate from the predictions of this law, especially under high pressures or low temperatures, where gas molecules interact more.

Tetracarbonylnickel

Tetracarbonylnickel, or Ni(CO)_4 , is a crucial compound in the nickel refining process due to its unique properties. It is formed by the reaction of solid nickel with carbon monoxide gas. This compound displays exceptional volatility, boiling at relatively low temperatures of around 43°C, which transforms it into a gaseous state.

This volatile nature is particularly useful in metallurgical processes. When heated above its boiling point, it breaks down into nickel and carbon monoxide, allowing the nickel to be extracted in its pure form. The process utilizes the decomposition to retrieve the nickel, while the carbon monoxide can be used in a closed-loop system, minimizing waste.

Moreover, the molecular structure of Ni(CO)_4 , comprised of a nickel atom surrounded by four carbon monoxide molecules, contributes to its stability and volatility. This property is exploited in industries for efficient nickel purification, utilizing physical and chemical characteristics of tetracarbonylnickel.