Question

Using IUPAC norms write the formulas for the following: Hexaamminecobalt (III) sulphate.

Answer 1

Hint: IUPAC stands for International union of pure and applied chemistry. It has named the compounds according to their structural positions. A chemical complex consists of a central metal, along with surrounding ligands. The naming is done according to the rules for complexes.

Complete answer: IUPAC has made certain norms for naming of compounds. Hexaamminecobalt (III) sulphate is a complex, which is named according to its constituent central atom and ligands.
The naming of complexes, according to IUPAC is:
- Name of the cation is written before the name of the ligands. Then ligands are stated in alphabetical order.
- di, tri, tetra, penta, hexa, etc. is written before the ligand name in simple ligands. While for complex ligands, bis, tris, tetrabis, etc. are written.
- The negative ligands have ‘o’ put at the end. Like, sulphate becomes sulphato.
- Roman numeral written indicates the oxidation number of the central atom.
- For anionic complexes, the central atom name has ‘ate’ at the end, while cationic complexes remain the same name as that of the central atom.
Now we are given Hexaamminecobalt (III) sulphate, which means it contains 6 amino groups that are $N{{H}_{3}}$. Then it has a metal Cobalt with valency of 3, and the ligand sulphate.
So, according to rules, Cobalt is written first, then the ligand amino, and then sulphate. So, the formula will be written as:
\[{{[Co{{(N{{H}_{3}})}_{6}}]}_{2}}{{(S{{O}_{4}})}_{3}}\]
Hence, the formula of Hexaamminecobalt (III) sulphate is \[{{[Co{{(N{{H}_{3}})}_{6}}]}_{2}}{{(S{{O}_{4}})}_{3}}\].

Note: The subscript outside the bracket of cobalt and amine, 2 denotes the valency of sulphate, while the subscript outside the bracket of sulphate, which is 3 denotes the valency of cobalt as (III).