Animated Solution for Chemistry - Coordination Compounds: The equation which is balanced and represents the correct product(s) is

A Test of Chemical Intuition

Imagine you are a chemical detective presented with four suspect equations. Your job is to find the one that is chemically feasible and stoichiometrically balanced.

This isn't just about counting atoms; it's about understanding the underlying chemical principles. We need to evaluate acid-base strength, charge conservation, and redox behavior.

Let's put these equations under the microscope.

The Battle of Bases

Our first suspect is the reaction between lithium oxide and potassium chloride.

At first glance, it looks like a simple double displacement. But we must consider the acid-base strength of the oxides.

As we move down the alkali metal group, the metal-oxygen bond becomes more ionic, making the oxide a stronger base. Therefore, potassium oxide is a much stronger base than lithium oxide.

A fundamental rule of chemistry is that a weaker base cannot spontaneously generate a stronger base. Thus, this reaction is a chemical dead end.

The Charge Trap

Next, we examine the reaction of the magnesium aqua complex with EDTA.

The reaction itself is a classic ligand substitution, but look closely at the product's charge.

Magnesium is in the $+2$ oxidation state, and the fully deprotonated EDTA ligand carries a $-4$ charge.

By simple charge conservation, the net charge of the resulting complex must be the sum of these charges: $+2+(-4)=-2$.

The equation incorrectly shows a $+2$ charge for the product. The correct product is $[\text{Mg}(\text{EDTA}){]}^{2-}$. This option is a classic trap!

The Hidden Redox Reaction

Now, let's look at the interaction between copper sulphate and potassium cyanide.

You might expect cyanide to simply replace the sulphate and water ligands to form a tetracyanocuprate(II) complex. However, cyanide is a pseudohalide and a strong reducing agent.

When it encounters the oxidizing Cu(II) ion, a redox reaction takes precedence over simple complexation. Cyanide reduces Cu(II) to Cu(I), forming insoluble copper(I) cyanide and releasing cyanogen gas.

Because of this hidden redox behavior, a stable Cu(II) cyanide complex is not formed. This equation is chemically flawed.

The Acidic Demise of Ammine Complexes

Finally, we arrive at the cobalt ammine complex in an acidic medium.

Ammonia is a Lewis base. When an ammine complex is placed in a strongly acidic environment, the abundant hydrogen ions attack the ammonia ligands.

The ammonia is protonated to form the ammonium ion (${\text{NH}}_4^{+}$). Because the ammonium ion lacks a lone pair, it can no longer act as a ligand, causing the coordination sphere to collapse.

The complex decomposes, releasing the central cobalt(II) ion and the chloride ion. This equation perfectly captures this chemical reality and is stoichiometrically balanced.

After rigorously testing each equation against the laws of chemistry, only one stands strong.

The decomposition of the ammine complex in acid is the only chemically feasible and balanced reaction.