Problem 182 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the following \begin{tabular}{ll} \hline Column-I & Column-II \\ \hline (a) \(\mathrm{H}_{3} \mathrm{PO}_{4}\) & (p) Can react with \(\mathrm{AgNO}_{3}\) \\ (b) \(\mathrm{HPO}_{3}\) & (q) In water softener \\ (c) \(\mathrm{H}_{4} \mathrm{P}_{2} \mathrm{O}_{7}\) & (r) \(\mathrm{sp}^{3}\) hybridisation \\ (d) \(\mathrm{H}_{3} \mathrm{PO}_{2}\) & (s) Monobasic \\ \hline \end{tabular}

Step-by-Step Solution

Answer

(a)-q, (b)-p, (c)-r, (d)-s

Step 1: Examine H3PO4

Phosphoric acid, \( ext{H}_{3} ext{PO}_{4}\), is used in water treatment processes such as water softening due to its ability to remove cations. Therefore, it matches with \( ext{q})\).

Step 2: Examine HPO3

Metaphosphoric acid, \( ext{HPO}_{3}\), has a simple structure leading to a linear phosphate, and it cannot be easily matched directly to any option without context. It’s typically known to react with silver nitrate, so it aligns with \( ext{p})\).

Step 3: Examine H4P2O7

Pyrophosphoric acid, \( ext{H}_{4} ext{P}_{2} ext{O}_{7}\), has all four phosphorus atoms with \( ext{sp}^{3}\) hybridization forming a tetrahedral shape and thus, matches with \( ext{r})\).

Step 4: Examine H3PO2

Hypophosphorous acid, \( ext{H}_{3} ext{PO}_{2}\), is known to be monobasic as it contains one replaceable hydrogen atom in the form of an acid, therefore it matches with \( ext{s})\).

Key Concepts

H3PO4 (Phosphoric acid)

Phosphoric acid, chemically represented as \( \mathrm{H}_3 \mathrm{PO}_4 \), is a common oxyacid of phosphorus. It is widely used in various applications due to its ability to interact with ions in a solution. In water treatment, phosphoric acid acts as a water softener.
This is because it can effectively remove cations, which are positively charged ions found in hard water. By binding with these cations, phosphoric acid helps to prevent the formation of scale, which can accumulate and clog pipes and machinery.

• Used in water treatment
• Removes cations
• Prevents scale formation

This ability to remove cations makes \( \mathrm{H}_3 \mathrm{PO}_4 \) an important component in maintaining and improving the quality of water systems.

HPO3 (Metaphosphoric acid)

Metaphosphoric acid, represented as \( \mathrm{HPO}_3 \), is a fascinating compound with a unique structure. It is often used in contexts where dehydrating properties are needed.
Despite its simple formula, \( \mathrm{HPO}_3 \) can form long-chain structures or cyclic formations, where the phosphorus atoms connect in a loop. This structural property makes metaphosphoric acid useful in various chemical reactions.

• Has a simple structure
• Can form long chains
• React with silver nitrate

One of its notable reactions is with silver nitrate \( (\mathrm{AgNO}_3) \) where the acid helps in the precipitation of silver phosphate, a reaction useful in analytical chemistry for detecting phosphates.

H4P2O7 (Pyrophosphoric acid)

Pyrophosphoric acid, or \( \mathrm{H}_4 \mathrm{P}_2 \mathrm{O}_7 \), is known for having all its phosphorus centers in an \( \mathrm{sp}^3 \) hybridized state. This results in a tetrahedral geometry around each phosphorus atom.
The unique structure of pyrophosphoric acid enables it to participate in condensation reactions, in which it can link two molecules together with the loss of a water molecule. This makes it an important acid in chemical synthesis.

• \( \mathrm{sp}^3 \) hybridization
• Tetrahedral geometry
• Participates in condensation reactions

Its structural characteristics are integral in synthesizing various phosphate derivatives, making it a versatile component in industrial applications.

H3PO2 (Hypophosphorous acid)

Hypophosphorous acid, noted as \( \mathrm{H}_3 \mathrm{PO}_2 \), is an oxyacid of phosphorus that is distinct for being monobasic. This means it has only one hydrogen atom available to react as an acid.
This property is due to the acid's unique structure, where the hydrogen atom is bonded to a phosphorus atom, making it replaceable only under certain conditions.

• Monobasic nature
• Single replaceable hydrogen[/li]
• Used as a reducing agent

Hypophosphorous acid's monobasic nature also makes it an effective reducing agent in various chemical processes, where it helps in reducing metal salts to pure metals.