The difference between spin only magnetic moment values of [Co(H₂ O)₆]Cl₂ and [Cr(H₂ O)₆] Cl₃ is ___________.

Solution

Chemistry ma’am · 3 steps

Find the oxidation state, fill the d electrons with water as a weak-field ligand, and count unpaired ones.

1. Oxidation states. Water is neutral and each chloride is -1. So cobalt is Co²⁺ (3d⁷) and chromium is Cr³⁺ (3d³).
2. Fill the orbitals. H₂O is a weak-field ligand, so Δₒ is small and Co²⁺ stays high spin. For Cr³⁺ the three electrons go singly into t_(2g) whatever the field strength.

   Complex	d configuration	Unpaired electrons	μ = √n(n+2)
   [Co(H₂O)₆]Cl₂	t_(2g)⁵ e_g²	3	√15 = 3.87 BM
   [Cr(H₂O)₆]Cl₃	t_(2g)³ e_g⁰	3	√15 = 3.87 BM

3. So. Both complexes have 3 unpaired electrons and the same spin-only moment of 3.87 BM. The difference is 0.

The common slip: 2.14. Treating Co²⁺ as low spin with 1 unpaired electron gives 3.87 - 1.73 = 2.14, but water is too weak a ligand to pair those electrons.

The idea to keep. Spin-only moment depends only on the number of unpaired electrons. Fix the oxidation state first, then let the ligand decide high or low spin for d⁴ to d⁷ ions.

Answer from the NTA final answer key. Solution by PrepWiser.