Animated Solution for Chemistry - s and p-Block Elements: With respect to hypochlorite, chlorate and perchlorate ions, choose the correct statement(s).

A Primer

Let's dive into this beautiful question about the oxoanions of chlorine. We have three key players here: the hypochlorite ion (${\text{ClO}}^{-}$), the chlorate ion (${\text{ClO}}_3^{-}$), and the perchlorate ion (${\text{ClO}}_4^{-}$).

We need to analyze their acidic strength, their molecular geometry, and their chemical reactions. This is a classic multi-concept problem that tests your fundamental understanding of inorganic chemistry. Let's take them one by one.

First, let's look at option A, which talks about conjugate base strength. To understand this, we must first look at their parent acids: hypochlorous acid ($\text{HClO}$), chloric acid (${\text{HClO}}_3$), and perchloric acid (${\text{HClO}}_4$).

Notice the oxidation state of chlorine in these acids. It goes from $+1$ in $\text{HClO}$, to $+5$ in ${\text{HClO}}_3$, to $+7$ in ${\text{HClO}}_4$. As the oxidation state increases, the electronegativity of the central chlorine atom increases. This pulls electron density away from the $\text{O-H}$ bond, making it easier to release an ${\text{H}}^{+}$ ion. So, perchloric acid is the strongest acid here.

Now, recall the fundamental rule of acid-base chemistry: a weaker acid always has a stronger conjugate base. Since hypochlorous acid is the weakest acid among the three, its conjugate base, the hypochlorite ion (${\text{ClO}}^{-}$), must be the strongest conjugate base. This makes perfect sense because the negative charge is least stabilized by resonance in hypochlorite. So, option A is absolutely correct.

VSEPR Theory in Action

Moving on to option B, let's analyze their molecular shapes. Look at the hypochlorite ion. It consists of just two atoms: one chlorine and one oxygen. Any molecule with only two atoms is strictly linear by default. The three lone pairs on the chlorine atom do not bend the molecule because there are no other atoms to push away. It's just a straight line.

Next, let's examine the chlorate ion (${\text{ClO}}_3^{-}$). The central chlorine atom forms three sigma bonds with oxygen atoms and has one lone pair remaining. This gives it a steric number of $4$, meaning $s{p}^3$ hybridization. Normally, $s{p}^3$ means tetrahedral, but because of that one lone pair sitting on top, the shape is distorted into a trigonal pyramid. So, the lone pair directly influences its shape.

Finally, look at the perchlorate ion (${\text{ClO}}_4^{-}$). The chlorine atom forms four sigma bonds with four oxygen atoms, and there are zero lone pairs left on the central atom. With a steric number of $4$ and no lone pairs, it adopts a perfect tetrahedral geometry. Therefore, out of the three, only the chlorate ion's shape is influenced by a lone pair. Option B is also correct.

Let's check option C, which is about disproportionation reactions. When hypochlorite ions are heated, they undergo disproportionation. This means the same species is both oxidized and reduced.

Three moles of hypochlorite react to give two moles of chloride ions and one mole of chlorate ions. Keep these products in mind.

Now, what happens when chlorate ions disproportionate?

Four moles of chlorate react to produce three moles of perchlorate ions and one mole of chloride ions. Compare the two sets of products. Hypochlorite gives chloride and chlorate, while chlorate gives chloride and perchlorate. The sets of ions are clearly not identical. So, option C is incorrect.

The Oxidizing Power of Hypochlorite

Lastly, let's evaluate option D. The hypochlorite ion is a well-known, strong oxidizing agent. When it reacts with a sulfite ion (${\text{SO}}_3^{2-}$), it oxidizes the sulfite to sulfate (${\text{SO}}_4^{2-}$), increasing the oxidation state of sulfur from $+4$ to $+6$.

In the process, hypochlorite itself gets reduced to a chloride ion. This is a classic redox reaction, making option D perfectly correct.

To wrap it all up, we have thoroughly analyzed all four statements. We found that the hypochlorite ion is indeed the strongest conjugate base, only the chlorate ion's shape is influenced by a lone pair, and hypochlorite successfully oxidizes sulfite. The only incorrect statement was about the disproportionation products. Therefore, the correct options are (A), (B), and (D).