Question

In borax bead test which compound is formed (a) ortho borate (b) meta borate (c) double oxide (d) tetra borate

Short answer

(b) meta borate

Step-by-step solution

Understanding the Borax Bead Test

The borax bead test is a qualitative analysis technique used to identify certain metal ions. When borax is heated in a flame, it forms a glass-like bead that can dissolve metal oxides.

Reaction of Borax in Flame

When borax, chemically sodium tetraborate ( ext{Na}_2 ext{B}_4 ext{O}_7), is heated, it loses its water of crystallization and transforms into boric anhydride ( ext{B}_2 ext{O}_3), which forms the bead.

Formation of Metal Metaborate

The boric anhydride from borax reacts with metal oxides to form metal metaborate compounds, giving the bead characteristic colors, depending on the metal ion present.

Key concepts

Qualitative Analysis

Qualitative analysis is a branch of chemistry focused on identifying the chemical constituents of substances, usually without quantifying them. One common method of qualitative analysis is the Borax Bead Test. This test is mainly used to identify specific metal ions based on their ability to form colored compounds when heated. Understanding qualitative analysis helps chemists determine the composition of a sample through simple observations.

The Borax Bead Test falls under qualitative analysis as it uses heat and a simple reagent—borax—to reveal qualitative information about metal ions. By observing the color and behavior of a heated borax bead, chemists can conclude which metal ions are present in a sample. The process does not measure how much of the ion is present, only if it exists in the sample.

Metal Ions Identification

Identifying metal ions is crucial for various applications in chemistry, such as mineral analysis and material science. In the Borax Bead Test, this identification is achieved by examining the color emitted by the bead.

When borax is heated, it forms a bead that can bind with metal ions from a sample. Each metal ion may result in a characteristic color due to the formation of metal metaborates. Here are a few examples:

• Cobalt ions yield a blue bead, indicating the presence of cobalt.
• Copper ions produce a green bead, revealing copper in the material.
• Chromium ions can result in a green bead but differ slightly from copper.

This test allows quick field identification without needing complex equipment. Various ions give different colors when tested with the borax bead method. This makes it a useful technique for initial metal ion analysis.

Metal Metaborate Formation

During the Borax Bead Test, metal metaborate formation is key to the test's ability to identify metal ions. When borax, or sodium tetraborate, is heated, it breaks down into boric anhydride and sodium metaborate.

The heat causes boric anhydride to react with metal oxides present in the sample, forming metal metaborates. This chemical transformation is essential for the test. It allows the bead to display specific colors when held in the flame.

The reaction can be simplified as:
\[ \text{B}_2\text{O}_3 + \text{MO} \rightarrow \text{M(BO}_2)_2 \]

Here, \( \text{MO} \) represents a metal oxide, and \( \text{M(BO}_2)_2 \) is the metal metaborate formed. This compound's presence is what causes the bead to exhibit characteristic colors when specific metal ions are present. The distinct colors seen during the test arise from the light absorption and emission characteristics of the metal metaborate, making it straightforward to deduce which metal ions are in a sample.