Chemistry Q68 – NEET-UG 2026

Home Chemistry Coordination CompoundsQuestion #358

The formula of tetraammineaquachloridocobalt(III) chloride is

Clue 1 of 3: IUPAC Nomenclature

Understand the rules for naming coordination compounds, including identifying the central metal, ligands, and their charges.

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Ninja Strategy•Systematic Nomenclature and Charge Balance

Break down the name to identify the central metal, its oxidation state, and all ligands to determine the complex ion's formula and charge, then balance with the correct number of counter ions.

🧠 Full Solution Path

Step 1: Identify Components from Name✦ Active

The name "tetraammineaquachloridocobalt(III) chloride" provides the following information: - Central metal: Cobalt (Co) - Oxidation state of Co: $+ 3$ - Ligands inside the coordination sphere: four ammine ( $N H_{3}$ ), one aqua ( $H_{2} O$ ), one chlorido ( $C l^{-}$ ). - Counter ion outside the coordination sphere: chloride ( $C l^{-}$ ).

💡 Teacher's Secret Hint

Remember that 'ammine' refers to $N H_{3}$ , 'aqua' to $H_{2} O$ , and 'chlorido' to $C l^{-}$ . The Roman numeral (III) indicates the oxidation state of the central metal.

Step 2: Determine the Charge of the Complex Ion○ Expand

The complex ion is formed by the central metal and its ligands: $[C o (N H_{3})_{4} (H_{2} O) C l]$ . Let's calculate its charge: - Charge of $C o = + 3$ - Charge of $N H_{3} = 0$ (neutral ligand) - Charge of $H_{2} O = 0$ (neutral ligand) - Charge of $C l^{-} = - 1$ Overall charge of the complex ion = $(+ 3) + 4 (0) + 1 (0) + 1 (- 1) = + 3 - 1 = + 2$ . So, the complex ion is $[C o (N H_{3})_{4} (H_{2} O) C l]^{2 +}$ .

💡 Teacher's Secret Hint

Neutral ligands like $N H_{3}$ and $H_{2} O$ do not contribute to the charge of the complex ion.

Step 3: Formulate the Complete Compound○ Expand

Since the complex ion has a $+ 2$ charge, $[C o (N H_{3})_{4} (H_{2} O) C l]^{2 +}$ , and the counter ion is chloride ( $C l^{-}$ ), two chloride ions are needed to balance the $+ 2$ charge of the complex ion. Therefore, the complete formula for the compound is $[C o (N H_{3})_{4} (H_{2} O) C l] C l_{2}$ .

💡 Teacher's Secret Hint

The total positive charge must equal the total negative charge for a neutral compound.

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Chemistry Question 68 – NEET-UG 2026

Clue 1 of 3: IUPAC Nomenclature

🧠 Full Solution Path