Problem 18 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The transition metal ions responsible for colour in ruby and emerald are, respectively: (a) \(\mathrm{Co}^{3+}\) and \(\mathrm{Cr}^{3+}\) (b) \(\mathrm{Co}^{3+}\) and \(\mathrm{Co}^{3+}\) (c) \(\mathrm{Cr}^{3+}\) and \(\mathrm{Cr}^{3+}\) (d) \(\mathrm{Cr}^{3+}\) and \(\mathrm{Co}^{3+}\)

Step-by-Step Solution

Answer

The correct answer is (c) \(\mathrm{Cr}^{3+}\) and \(\mathrm{Cr}^{3+}\).

Step 1: Understand the Problem

We need to identify the transition metal ions that are responsible for the colors in both ruby and emerald. We have four options with different ions that we need to evaluate.

Step 2: Recall the Gemstone Colors

Rubies are known for their deep red color, and the main metal ion responsible for this color is chromium (\(\mathrm{Cr}^{3+}\)). Emeralds are known for their green color, which is also due to chromium (\(\mathrm{Cr}^{3+}\)).

Step 3: Analyze the Options

Based on our information that both ruby and emerald get their colors from chromium ions, we evaluate the options: - Option (a) is incorrect because it lists cobalt for ruby. - Option (b) is incorrect because it lists cobalt for both. - Option (c) lists chromium for both, which matches our information. - Option (d) is incorrect because it lists cobalt for emerald.

Step 4: Select the Correct Option

From the analysis, Option (c) is the only correct choice since it correctly identifies \(\mathrm{Cr}^{3+}\) as the ion responsible for both ruby and emerald colors.

Key Concepts

Gemstone Colors

Gemstones come in a wide array of stunning colors that catch the eye and capture the heart. The colors in gemstones are primarily due to light interacting with elements within the crystal structure. Various transition metal ions play a significant role in these colors. Transition metals are known for their ability to form various oxidation states, which can lead to different colors in minerals.

In nature:

• Ruby is renowned for its rich, deep red hue.
• Emerald captivates with its vivid, lush green tone.

These colors are not due to any surface pigments but are instead embedded within the stone itself, caused by specific metal ions. Understanding the intricacies of these colors can lead one to appreciate the beautiful science behind gemstones.

Chromium Ions

Chromium ions, particularly trivalent chromium ({\(\mathrm{Cr}^{3+}\)}), are essential for the enchanting colors of many gemstones. These ions can replace other metal ions within a crystal lattice, altering the way light is absorbed and leading to color changes. The ability of chromium ions to cause such dramatic color changes is due to crystal field theory. This theory describes how electron clouds surrounding these ions affect color.

Key properties of chromium ions include:

• Chromium ions can exist in several states, but it's the {\(\mathrm{Cr}^{3+}\)} state that's crucial for ruby and emerald.
• The element chromium itself is metallic but shines through the gems in vibrant colors when in the right oxidation state.

Thus, chromium ions play a pivotal role in the unique, natural beauty found in gemstones like rubies and emeralds.

Ruby Color

Rubies are celebrated for their remarkable red color, which is due to the presence of chromium {\(\mathrm{Cr}^{3+}\)} ions in the mineral corundum. The deep red color, often associated with passion and power, emerges when chromium ions absorb light wavelengths, allowing red light to reflect back to our eyes.

Important aspects about ruby's color origin:

• Rubies are primarily composed of the mineral corundum, which is otherwise colorless until a metal like chromium is introduced.
• The interaction of the crystalline structure with the chromium ions creates the hallmark deep red hue.
• This specific red color can vary slightly depending on the amount and type of chromium present in the ruby.

So, the enchanting red color of a ruby is a prime example of how specific ions in their crystal lattice contribute to gemstone coloration.

Emerald Color

Emeralds are treasured for their lush green color, which is fundamentally caused by chromium {\(\mathrm{Cr}^{3+}\)} ions. Just like in rubies, these ions in emeralds alter the light absorption properties of the mineral, causing us to see their iconic green color.

Some interesting points about emerald's color origin:

• Emeralds are a type of beryl that acquires its green hue from trace amounts of chromium or sometimes vanadium.
• The interaction between the chromium ions and the beryl lattice structure is what gives this gemstone its vibrant green color.
• Emeralds can range from a light to a deep green, depending on chromium concentration and the presence of other impurities.

Overall, chromium ions are again the secret ingredient that imparts emeralds with their dazzling and unique green beauty.