Question

The compound formed in the borax bead test of \(\mathrm{Cu}^{2+}\) ion in oxidizing flame is (a) \(\mathrm{CuBO}_{2}\) (b) \(\mathrm{Cu}\left(\mathrm{BO}_{2}\right)_{2}\) (c) \(\mathrm{Cu}\) (d)none of these

Short answer

The compound formed is (b) \( \mathrm{Cu}\left(\mathrm{BO}_{2}\right)_{2} \).

Step-by-step solution

Understand the Borax Bead Test

The borax bead test is a qualitative analysis method used to detect certain metal ions. A bead is formed by melting borax and exposing it to a flame. The color and composition of the resulting bead indicate the metal ions present.

Identify the Role of the Oxidizing Flame

In the oxidizing flame, metal ions typically react with boron compounds to form complex borates. The oxidizing conditions can lead to the formation of metal oxides and borate complexes.

Consider the Behavior of 9u^{2+} Ions

When exposed to an oxidizing flame during the borax bead test, 9u^{2+} ions form a green bead. This color results from the formation of copper borate complexes.

Determine the Correct Compound for 9u^{2+} in Oxidizing Flame

Given the choices and the behavior of 9u^{2+} ions under oxidizing conditions, the compound formed is typically 9u ext{(BO}_2 ext{)}_2, which corresponds to the formation of a copper borate complex.

Key concepts

Copper(II) ions

Copper(II) ions, represented as \(Cu^{2+}\), are metal ions that have lost two electrons, resulting in a positive charge. In chemistry, these ions are quite significant due to their vibrant blue color in solution and their ability to form various complex compounds. The presence of copper(II) ions can be detected in several ways, one of which involves qualitative analysis techniques like the borax bead test.

In the borax bead test, copper(II) ions interact with borate ions to form metal borates, producing a distinct green color under certain conditions. This color change is a useful characteristic in lab settings, allowing scientists to confirm the presence of \(Cu^{2+}\) ions in a sample. Their behavior in different tests is fundamental for teaching and learning qualitative analysis techniques in chemistry.

Oxidizing flame

An oxidizing flame is a state of a flame in which there is an excess of oxygen. In such a flame, oxygen-rich conditions lead to the full combustion of substances and formation of metal oxides when metal salts are heated.

In experiments like the borax bead test, the oxidizing flame is used to drive reactions that involve metal ions. The metal ions, when exposed to an oxidizing flame, combine with oxygen to form metal oxides or metal borates. This oxidation process is key in influencing the types of compounds a metal ion can form, as well as the colors these compounds exhibit.

• A blue or outer part of the flame typically represents an oxidizing flame condition.
• Metal ions can show varying colors when exposed to different parts of the flame, a principle used in flame tests and other qualitative analyses.

Understanding how oxidizing flames interact with metal ions is essential for accurate interpretation of results in tests like the borax bead test.

Qualitative analysis

Qualitative analysis in chemistry is the process of identifying the chemical composition of substances. Unlike quantitative analysis, which measures how much of a substance is present, qualitative analysis determines what components are in a sample.

• This analysis often involves color tests, like the borax bead test, where metal ions are identified based on color changes.
• It is widely used for metal ions detection in solutions, offering visual indicators of the presence of specific ions.

Combining techniques such as heat, flame tests, and reagents, qualitative analysis can provide informative, straightforward methods to determine a sample's components.

The borax bead test is a prime example of qualitative analysis at work. It allows students and researchers to infer the presence of metal ions by observing color changes in borax beads heated in a flame. For copper(II), observing a green bead formation indicates successful identification.

Metal borates

Metal borates are compounds formed when metal ions react with borate ions. These compounds are significant in many chemical processes and have distinct, recognizable colors that can be used for identification.

• Metal borates are formed when melted borax reacts with metal ions and are often used in bead tests.
• The formed metal borates can sometimes show luminescent properties, depending on the metal involved.

In the context of a borax bead test, copper(II) ions form a copper borate compound, \(Cu(BO_2)_2\), when exposed to an oxidizing flame. This reaction results in a distinctive green-colored bead. Understanding the formation and characteristics of metal borates helps chemists and students to use simple qualitative tests to identify metals. It's a foundational concept that enables better understanding of metal behaviors in different chemical environments.