Question

The formula of tris (ethane -1,2- diamine) cobalt (III) sulphate is:

• A. \( [Co(H_2NCH_2CH_2NH_2)]_3SO_4 \)
• B. \( [Co(H_2NCH_2CH_2NH_2)]_2(SO_3)_3 \)
• C. \( [Co(CH_3CHNHNH_2)_3]_2(SO_4)_3 \)
• D. \( [Co(H_2NCH_2CH_2NH_2)_3]_2(SO_4)_3 \)

Hint:

Break down the IUPAC name of the coordination compound into its components: the central metal ion, the ligands, the oxidation state of the metal ion, and the counter ion. Use the charges of the complex ion and the counter ion to write the neutral formula of the compound, ensuring that the total positive and negative charges are equal. Remember the formulas and charges of common ligands and polyatomic ions.

Answer 1

The Correct Option is D

The name of the complex is tris(ethane-1,2-diamine)cobalt(III) sulphate.
Let's break down the name to determine the formula: - "tris" indicates that there are three ligands of the type mentioned in the complex ion.
- "ethane-1,2-diamine" is the IUPAC name for ethylenediamine, which has the formula \( H_2NCH_2CH_2NH_2 \).
We can abbreviate it as "en".
So, the complex ion contains three "en" ligands.
- "cobalt (III)" indicates that the central cobalt (Co) metal ion has an oxidation state of +3.
- The complex ion is enclosed in square brackets, and the ligands are attached to the central metal ion.
Thus, the complex ion is \( [Co(en)_3]^{3+} \) or \( [Co(H_2NCH_2CH_2NH_2)_3]^{3+} \).
- "sulphate" indicates that the counter ion is the sulphate ion, which has the formula \( SO_4^{2-} \) and a charge of -2.
To form a neutral compound, the total positive charge from the complex ion must balance the total negative charge from the sulphate ions.
The complex ion \( [Co(en)_3]^{3+} \) has a +3 charge.
To balance the charge with \( SO_4^{2-} \) ions, we need to find the least common multiple of the charges, which is 6.
To get a total positive charge of +6, we need 2 units of the \( [Co(en)_3]^{3+} \) ion: \( 2 \times (+3) = +6 \).
To get a total negative charge of -6, we need 3 units of the \( SO_4^{2-} \) ion: \( 3 \times (-2) = -6 \).
Therefore, the formula of the compound is \( [Co(H_2NCH_2CH_2NH_2)_3]_2(SO_4)_3 \).
Looking at the options:
Option (A) \( [Co(H_2NCH_2CH_2NH_2)]_3SO_4 \): The charges are \( +3 \times 3 = +9 \) and \( -2 \times 1 = -2 \), not balanced.

Option (B) \( [Co(H_2NCH_2CH_2NH_2)]_2(SO_3)_3 \): The counter ion is sulphite (\( SO_3^{2-} \)), not sulphate.

Option (C) \( [Co(CH_3CHNHNH_2)_3]_2(SO_4)_3 \): The ligand is incorrect (it's not ethane-1,2-diamine).

Option (D) \( [Co(H_2NCH_2CH_2NH_2)_3]_2(SO_4)_3 \): The complex ion and the counter ion are correct, and the charges are balanced (\( 2 \times (+3) + 3 \times (-2) = 0 \)).