Question

With which cation alizarin will impart a blue colour on the fabric? (a) \(\mathrm{Fe}^{3+}\) (b) \(\mathrm{Al}^{3+}\) (c) \(\mathrm{Cr}^{3+}\) (d) \(\mathrm{Ba}^{2+}\)

Short answer

Alizarin will impart a blue color with \\(\mathrm{Fe}^{3+}\)\u00B[0m.

Step-by-step solution

Understand Alizarin

Alizarin is a dye that can form colored complexes with various metal ions. The color imparted by alizarin depends on the type of metal ion it forms a complex with.

Consideration of Metal Ions

Alizarin typically forms a range of colored complexes depending on the metal: red with some, blue with others, etc. Your task is to determine which of the given metal ions forms a blue complex with alizarin.

Review of Potential Cations

Review the properties of each cation:- \(\mathrm{Fe}^{3+}\u00B[0m\): Known for forming dark blue or black complexes.- \(\mathrm{Al}^{3+}\u00B[0m\): Typically forms colorless or light complexes.- \(\mathrm{Cr}^{3+}\u00B[0m\): Can form a variety of colors.- \(\mathrm{Ba}^{2+}\u00B[0m\): Generally forms colorless or less vivid complexes.

Identify the Blue Complex Ion

From historical chemistry knowledge and typical dye interactions, \(\mathrm{Fe}^{3+}\u00B[0m\) is known to form blue or blue-black complexes with alizarin, making it the right answer.

Key concepts

Metal-Ion Complexes

Metal-ion complexes are fascinating structures in the realm of coordination chemistry. They consist of a central metal atom or ion bonded to surrounding molecules or ions called ligands. These ligands can be a variety of substances, including small molecules like water or larger organic compounds like dyes. One such dye is alizarin, which particularly forms complexes with metal ions.

When alizarin interacts with a metal ion, it acts as a ligand, and the type of metal ion determines the color of the complex. Metal ions such as \( \chi^{3+}\) or \( \chi^{2+}\) have different capacities to attract electrons, affecting the overall geometry and color of the complex.

• The coordination number, or the number of ligand bonds a metal center forms, influences the properties of the complex.
• Different metals have specific configurations that lead to unique interactions with ligands, explaining the distinctive colors that result.

In summary, the formation of metal-ion complexes is a key principle in explaining why certain substances have particular colors when used as dyes.

Colorimetric Analysis

Colorimetric analysis is a technique used to determine the concentration of colored compounds in solution. It is based on the principle that the concentration of a compound is directly proportional to the intensity of its color.

This method is often applied when working with metal-ion complexes to identify which metal ions are present or to measure their concentration. With alizarin dyes, this technique becomes especially useful due to the vivid colors these complexes exhibit.

The process involves:

• Adding the substance to a solvent or material until a clear color change occurs, indicating the presence of the specific metal ion.
• Using instruments like spectrophotometers that measure light absorption at specific wavelengths to determine the intensity of the color.

This analysis provides quantitative data that can reinforce visual observations made through experiments, making it a powerful tool in both research and educational settings.

Chromatic Coordination

Chromatic coordination refers to the relationship between the structure of a coordination complex and its observed color. This is a central theme in understanding interactions like those between alizarin and various metal ions.

All colors perceived in metal complexes arise from the electronic transitions within the metal and between the metal and ligands. Specifically, these transitions involve the difference in energy between electron orbitals, also known as d-d transitions or charge transfer transitions.

In practice, different metal ions will create different chromatic outcomes when forming complexes with dyes like alizarin:

• Fe\(^{3+}\) with alizarin, for example, forms a blue-black complex.
• Each metal ion brings a unique electronic structure, thus impacting color.

Understanding chromatic coordination helps chemists predict which metal-dye combinations will yield desired colors, which is crucial in industries like textiles where specific hues are sought after.

In essence, chromatic coordination demonstrates the delicate interplay between chemistry and visual art, revealing the beauty in scientific phenomena.