Question

Which of the following does not give borax bead test? (a) \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\) (b) \(\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2} \mathrm{Co}\) (c) \(\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}\) (d) \(\mathrm{NiSO}_{4}\)

Short answer

(c) \(\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}\) does not give the borax bead test.

Step-by-step solution

Understand the Borax Bead Test

The borax bead test is used to identify certain metal cations. When heated with borax, some transition metal ions give characteristic colors. This test is frequently applicable to transition metals, which often have partially filled d orbitals that can impact the outcome of the test.

Analyze Each Option

Consider each compound to determine if it contains a transition metal ion that would provide a characteristic color in the borax bead test:- (a) \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\) contains copper, a transition metal known for giving a blue-green color.- (b) \(\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2} \mathrm{Co}\) contains cobalt, a transition metal known for giving a blue color.- (c) \(\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}\) contains aluminum, which is not a transition metal and does not give color in the borax bead test.- (d) \(\mathrm{NiSO}_{4}\) contains nickel, a transition metal known for giving a brown or gray color.

Identify the Exception

As the borax bead test is suitable for transition metals and options \(a\), \(b\), and \(d\) contain transition metals that provide characteristic colors, we find that option \(c\) \(\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}\), which contains aluminum—a non-transition metal—does not satisfy the criteria.

Key concepts

Transition Metals and Their Characteristics

Transition metals are a group of elements located in the d-block of the periodic table. They are unique because they typically have one or more unpaired d-electrons. This feature leads to interesting properties such as the ability to form colorful compounds and a variety of oxidation states.
Due to these characteristics, transition metals are often used in various chemical tests and applications.
One of the notable aspects of transition metals is their tendency to form colored compounds. This occurs because the d-electrons can absorb visible light, causing electronic transitions. For example, copper compounds often display a blue or green color, while cobalt can show vibrant blues. Nickel, another transition metal, can appear brown or gray when used in tests like the borax bead test.
Transition metals are not just chemically diverse; they are also key components in catalysis and have significant industrial applications. Their fascinating ability to participate in complex formation makes them invaluable in both research and practical applications.

Identifying Metal Cations

When it comes to identifying metal cations, tests like the borax bead test are very helpful. This test is particularly effective for transition metals, which tend to form distinct, colorful beads when combined with borax upon heating.
The borax bead test involves heating a mixture of a metal salt and borax under a blue flame. Different metal cations, especially those from transition metals, will impart specific colors to the resulting bead. This technique allows for the quick identification of various metals.
For example:

• Copper gives a blue-green color.
• Cobalt results in a blue bead.
• Nickel produces brown or gray shades.

This method is not applicable to all metals. Non-transition metals like aluminum do not form colored beads, making them exceptions in such tests.
Understanding these properties enables chemists to efficiently determine the presence of certain metal ions, even in a complex mixture.

Laboratory Techniques in Chemistry

Conducting experiments in the laboratory requires a basic understanding of various techniques. The borax bead test, for instance, is a fundamental method used to identify metal ions through their color production upon heating with borax.
This technique involves creating a small borax bead on a wire, which is then coated with the metal salt. Upon heating, the bead melts and combines with the metal ions. A colored bead indicates the presence of a transition metal cation.
To perform the test:

• Heat a wire loop until it glows, then dip it in powdered borax.
• Heat again to form a clear borax bead on the loop.
• Dip the bead into the powdered metal salt and reheat it in the flame.
• Observe the resulting color.

Precision in this technique is critical. The flame's intensity and even the environment can affect outcomes. Hence, conducting the test under controlled conditions is essential for accurate results.
Techniques like these are not only vital for experiments but also for developing a deeper understanding of chemical properties and reactions.