Explain borax bead test ? with suitable example ?

The Borax Bead Test is a qualitative test used to identify certain metal ions in a sample. The test involves heating a small quantity of the sample on a platinum wire, which is dipped into a mixture of borax (sodium tetraborate) and water. The bead formed is then heated in a flame, and the color of the bead indicates the presence of specific metal ions.

Procedure

1. Preparation of the Borax Bead: A small amount of borax is taken on a platinum or nichrome wire and moistened with a few drops of water to form a paste. The wire is then heated in a Bunsen burner flame to form a clear, colorless bead.
2. Adding the Sample: A small amount of the metal salt or solution (containing metal ions) is taken and placed on the borax bead. The bead is then heated again in the flame, and the color of the bead changes based on the metal ion present in the sample.
3. Observation: The color of the bead is observed and compared with standard colors for different metals. The color change occurs due to the formation of a metal borate complex.

Examples

• Copper (Cu²⁺): The bead turns blue when heated.
• Iron (Fe³⁺): The bead may turn yellow in an oxidizing flame and green in a reducing flame.
• Chromium (Cr³⁺): The bead turns green.
• Cobalt (Co²⁺): The bead turns blue in a reducing flame.

Principle

The principle behind the Borax Bead Test lies in the fact that borax forms a colorless bead in the flame. When a metal salt is added, it forms a metal borate complex, which imparts a characteristic color to the bead. The color of the bead depends on the oxidation state of the metal ion and its interaction with borax.

Example

1. Copper Salt (Cu²⁺) in Borax Bead Test: A few drops of copper sulfate solution are added to the borax bead. Upon heating in the flame, the bead turns a bright blue. This indicates the presence of copper ions in the sample.
2. Iron Salt (Fe³⁺) in Borax Bead Test: Iron (III) chloride solution is used, and when placed on the borax bead and heated, the bead may turn yellow in an oxidizing flame and green in a reducing flame.

Uses:

• It is used primarily for the detection of transition metals, especially for ions of copper, iron, chromium, and cobalt.
• This test is helpful in qualitative inorganic analysis, where it helps in confirming the identity of metal ions in a given sample.