Question

In a borax bead test under hot condition, a metal salt (one from the given) is heated at point B of the flame, resulted in green colour salt bead. The spin-only magnetic moment value of the salt is ............... BM (Nearest integer) [Given atomic number of Cu = 29, Ni = 28, Mn = 25, Fe = 26]

Answer 1

5

Answer 2

The borax bead test is used to identify metal ions. A green color bead under hot conditions with the given options suggests either Copper(II) or Iron(II). Point B in the Bunsen burner flame diagram typically represents the reducing zone. In the reducing flame, Iron(II) ions (Fe²⁺) produce a pale green bead. Copper(II) ions (Cu²⁺) typically produce a green bead in the oxidizing flame. Given the options and the flame zone indicated, Iron is the more likely metal.

The atomic number of Iron (Fe) is 26. Its electronic configuration is [Ar] 3d⁶ 4s². In the reducing flame, it forms Fe²⁺, which has the electronic configuration [Ar] 3d⁶.

To find the number of unpaired electrons (n) for Fe²⁺ (3d⁶): The 3d orbitals are filled as follows: $\text{3d: } \underset{\uparrow}{\text{d}_{xy}} \quad \underset{\uparrow}{\text{d}_{yz}} \quad \underset{\uparrow}{\text{d}_{xz}} \quad \underset{\uparrow}{\text{d}_{x^2-y^2}} \quad \underset{\phantom{\uparrow}}{\text{d}_{z^2}}$ There are 4 unpaired electrons (n = 4).

The spin-only magnetic moment ($\mu_s$) is calculated using the formula: $\mu_s = \sqrt{n(n+2)} \text{ BM}$ Substituting n = 4: $\mu_s = \sqrt{4(4+2)} = \sqrt{4 \times 6} = \sqrt{24} \text{ BM}$ $\sqrt{24} \approx 4.899 \text{ BM}$ The nearest integer to 4.899 is 5.

Therefore, the spin-only magnetic moment value of the salt is 5 BM.