Problem 27 - Chemistry in 30 days

Question

Nickel is purified by thermal decomposition of its (a) Hydride (b) Chloride (c) Azide (d) Carbonyl

Step-by-Step Solution

Answer

Nickel is purified by thermal decomposition of its carbonyl.

Step 1: Understand the Context

Nickel is a metal that can be purified by removing impurities. Different chemical compounds of nickel can be thermally decomposed to obtain pure nickel.

Step 2: Analyze the Options

Let's look at the given options: Hydride, Chloride, Azide, and Carbonyl. These are all compounds of nickel, and one of them, when decomposed by heat, results in the purification of nickel.

Step 3: Evaluate Carbonyl Decomposition

Nickel carbonyl is a well-known compound used in nickel purification. It can be decomposed thermally to produce pure nickel metal.

Step 4: Confirm the Correct Answer

Thermal decomposition of nickel carbonyl (Ni(CO)_4) at high temperatures breaks down into pure nickel and carbon monoxide gas: \[ \text{Ni(CO)}_4 \rightarrow \text{Ni} + 4\text{CO} \]. This process is known as the Mond process.

Key Concepts

Thermal decomposition

Thermal decomposition is a chemical process where a compound breaks down into simpler substances when heated. In the context of nickel purification, this involves using heat to decompose compounds of nickel, such as nickel carbonyl, to obtain pure nickel.
Here’s how it works: when a compound like nickel carbonyl is heated, it breaks apart into nickel metal and carbon monoxide gas. This happens because the heat provides the energy needed to break the chemical bonds within the compound.
This method is favored because it allows for the separation of nickel in a very pure form. For nickel carbonyl, the reaction can be expressed as:

• Ni(CO)_4 ightarrow ext{Ni} + 4 ext{CO}

Thermal decomposition is especially useful in metal purification, as it provides a way to isolate metals from their compounds by applying heat.

Nickel carbonyl

Nickel carbonyl, also known by its chemical formula Ni(CO)_4, is a colorless liquid compound that plays a crucial role in the purification of nickel. It was the first metal carbonyl to be discovered and is valued for its volatility and ability to decompose cleanly.
Nickel carbonyl is formed when carbon monoxide is passed over powdered nickel at room temperature. This creates a volatile compound that can easily be transported and then decomposed to release pure nickel.
Because it is volatile, nickel carbonyl can be decomposed at relatively low temperatures compared to other nickel compounds, making it very efficient for extracting nickel. When heated, it breaks down into nickel and carbon monoxide gas, making it an ideal compound for nickel purification in the Mond process.

Mond process

Named after Ludwig Mond, the Mond process is an industrial technique for purifying nickel. It exploits the chemical properties of nickel carbonyl, formed when nickel reacts with carbon monoxide. Here are the key steps in the Mond process:

• Impure nickel is converted to nickel carbonyl by exposing it to carbon monoxide. This occurs at around room temperature, forming a gas.
• The nickel carbonyl gas is then subjected to higher temperatures, causing it to decompose. This decomposition releases pure nickel, leaving carbon monoxide gas as a byproduct.

The Mond process is highly efficient because it allows nickel to be purified at a lower temperature than most other metal purification methods. It is particularly useful in producing nickel for high-purity applications, such as coinage and the production of stainless steel. The simplicity and effectiveness of using nickel carbonyl make the Mond process a cornerstone in metallurgy for nickel extraction and purification.