Problem 149 - A Complete Resource Book in Chemistry for JEE Main

Question

The colour of bead \(\mathrm{Ni}\left(\mathrm{BO}_{2}\right)_{2}\) is of (a) Brown (b) Blue (c) Green (d) Violet

Step-by-Step Solution

Answer

The color of \(\mathrm{Ni}\left(\mathrm{BO}_{2}\right)_{2}\) is green.

Step 1: Understand the Composition

The compound given is nickel(II) metaborate, represented by the formula \(\mathrm{Ni}\left(\mathrm{BO}_{2}\right)_{2}\). The key component here is the nickel ion (\(\mathrm{Ni}^{2+}\)), which is known for imparting distinct colors to compounds.

Step 2: Recall Nickel Ion Characteristics

The \(\mathrm{Ni}^{2+}\) ion, typically found in various nickel compounds, often gives rise to characteristic colors. Most commonly, nickel compounds with the \(\mathrm{Ni}^{2+}\) ion are associated with green or bluish-green colors.

Step 3: Determine the Expected Color

Based on the known color characteristics of the \(\mathrm{Ni}^{2+}\) ion, and given the structure of \(\mathrm{Ni}\left(\mathrm{BO}_{2}\right)_{2}\), it's typical for nickel compounds in similar chemical environments to appear green.

Key Concepts

Nickel ion color

Nickel ions, specifically the nickel(II) ion denoted as \(\mathrm{Ni}^{2+}\), are renowned for imparting distinctive colors to various compounds. These colors are a result of transitions of electrons between different energy levels within the nickel ion. Such transitions occur when light interacts with the compound, absorbed light results in perceptible color changes.

Typically, \(\mathrm{Ni}^{2+}\) exhibits green or bluish-green hues in many compounds. The presence of \(\mathrm{Ni}^{2+}\) in different environments can slightly alter its color due to changes in the electronic surroundings.

• In aqueous solutions, \(\mathrm{Ni}^{2+}\) is often associated with a green color.
• Partial substitution or complexation, like in crystals or glass formation, can shift the observed color.

Understanding how ions like \(\mathrm{Ni}^{2+}\) interact with their environments clarifies why nickel-based compounds exhibit their characteristic hues.

Nickel(II) metaborate

Nickel(II) metaborate, chemically written as \(\mathrm{Ni(BO_2)_2}\), is a compound featuring both nickel and borate components. The structure of this compound significantly influences its properties and resulting appearance.

Nickel(II) metaborate is formed by combining nickel with boron oxide in a specific ratio, with nickel acting as a central metal ion surrounded by borate groups. These borate groups impact the electrochemical environment of the nickel ion, thereby influencing the compound's color.

• The borate group \((\mathrm{BO_2}^-)\) is integral in stabilizing the nickel ion.
• Formed through fusion, these compounds can exist in crystalline or amorphous forms, affecting color perception.

The presence of nickel in conjunction with borate impacts not only color but also the overall stability and chemical behavior of the compound.

Ni(BO2)2 color determination

Determining the color of nickel(II) metaborate \((\mathrm{Ni(BO_2)_2})\) involves understanding the distinct contributions of its components. Due to the electronic transitions of \(\mathrm{Ni}^{2+}\) ions, as mentioned earlier, the expected color typically aligns with its green hue.

In nickel(II) metaborate, the nickel ion is ensconced within the borate framework, lending it certain physical and chemical characteristics necessary for color determination. Laboratory synthesis and observation are essential to confirm and analyze these predictions.

In controlled environments where this compound is synthesized:

• Natural light or specific wavelengths can be used to view the compound color.
• Green is often the observed color, aligning with the typical characteristics of nickel compounds.

By using scientific methodologies, the expected lightweight green tint of \(\mathrm{Ni(BO_2)_2}\) can be visually confirmed.