Tris (ethane-1,2-diammine) cobalt (III) sulphate is :

Question

Accepted Answer

Tris (ethane-1,2-diammine) cobalt (III) sulphate is a coordination compound where cobalt is coordinated with three ethane-1,2-diamine (en) ligands, and the compound is associated with sulphate ions. Let's analyze why Option 4 is the correct representation of this compound:

1. **Option 4: $[Co(en)_{3}]_{2}(SO_{4})_{3}$**
   - This option correctly represents the compound as a complex ion with cobalt (III) coordinated to three ethane-1,2-diamine ligands. The notation $[Co(en)_{3}]$ indicates that each cobalt ion is surrounded by three bidentate ethane-1,2-diamine ligands, forming a stable octahedral complex.
   - The compound is a sulphate salt, and the formula $[Co(en)_{3}]_{2}(SO_{4})_{3}$ indicates that there are two such cobalt complexes for every three sulphate ions. This stoichiometry is consistent with the charge balance, as each cobalt (III) complex carries a +3 charge, and each sulphate ion carries a -2 charge. Therefore, two cobalt complexes (+6 total charge) balance with three sulphate ions (-6 total charge), making the compound electrically neutral.

2. **Option 1: $[Co(en)_{3}]SO_{4}$**
   - This option suggests a 1:1 ratio between the cobalt complex and the sulphate ion. However, this does not satisfy the charge balance. The cobalt complex $[Co(en)_{3}]^{3+}$ would require three sulphate ions to balance the charge, not one.

3. **Option 2: $[Co(en)_{3}]_{3}(SO_{4})_{2}$**
   - This option implies a 3:2 ratio between the cobalt complexes and sulphate ions. The total positive charge from three cobalt complexes would be +9, while the total negative charge from two sulphate ions would be -4. This does not achieve charge neutrality.

4. **Option 3: $[Co(H_{2}N-CH_{2}-CH_{2}-NH_{2})_{3}]_{2}(SO_{4})_{2}$**
   - Although this option correctly represents the ethane-1,2-diamine ligands in their full chemical form, it suggests a 2:2 ratio between the cobalt complexes and sulphate ions. This would result in a total positive charge of +6 from the cobalt complexes and a total negative charge of -4 from the sulphate ions, which does not balance.

In conclusion, Option 4 is the correct representation of tris (ethane-1,2-diammine) cobalt (III) sulphate because it accurately reflects the stoichiometry and charge balance required for the compound to be electrically neutral.