MCQ Detailed View

The borax bead test is a classical method used in qualitative inorganic analysis to detect the presence of certain metal ions, especially transition metals. In this test, borax (Na₂B₄O₇·10H₂O) is heated in a flame until it melts and forms a clear, colorless bead.

Upon heating, borax loses water and forms sodium metaborate (NaBO₂), commonly referred to as meta borate. The reaction involves the dehydration of borax:

Na₂B₄O₇ → 2 NaBO₂ + B₂O₃ + H₂O (on heating)

The molten bead of meta borate can then react with metal salts to produce colored complexes, which helps in the identification of metal ions. For example, cobalt gives a deep blue bead, while chromium produces a green bead.

Other compounds, such as ortho borate or tetra borate, are not formed in the borax bead test under typical heating conditions. The formation of meta borate is critical because it acts as a flux, lowering the melting point of metal oxides and allowing the formation of colored glass-like complexes in the bead.

This test is widely used in inorganic chemistry laboratories to qualitatively identify metal ions based on characteristic flame colors or bead color changes. Understanding the chemical changes in the borax bead test, specifically the formation of meta borate, helps students learn analytical techniques, coordination chemistry, and qualitative methods.

The borax bead test demonstrates how chemical transformations under heat can aid in identifying elements in compounds and provides a practical application of inorganic chemistry principles in metal analysis.