Problem 22 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The reaction of white phosphorus with aqueous \(\mathrm{NaOH}\) gives phosphine along with another phosphorus containing compound. The reaction type; the oxidation states of phosphorus in phosphine and the other product are respectively [2012] (a) redox reaction; \(-3\) and \(-5\) (b) redox reaction; \(+3\) and \(+5\) (c) disproportionation reaction; \(-3\) and \(+5\) (d) disproportionation reaction: \(-3\) and \(+3\)

Step-by-Step Solution

Answer

Answer is flawed; suggest error in provided options.

Step 1: Understand the Reaction

The reaction of white phosphorus (P4) with aqueous NaOH gives phosphine (PH3) and a sodium salt of hypophosphite (NaH2PO2). This is the overall reaction:\[P_4 + 3 ext{NaOH} + 3 ext{H}_2 ext{O} ightarrow ext{PH}_3 + 3 ext{NaH}_2 ext{PO}_2\]

Step 2: Identify Reaction Type

The reaction in question is a disproportionation reaction. In a disproportionation reaction, a single substance is simultaneously oxidized and reduced to form different products.

Step 3: Determine Oxidation States

Calculate the oxidation states of phosphorus in the reactants and products:- In white phosphorus (P4), phosphorus has an oxidation state of 0.- In phosphine (PH3), phosphorus has an oxidation state of \(-3\).- In NaH2PO2, phosphorus has an oxidation state of \(+1\).

Step 4: Compare Given Options

The reaction has been identified as a disproportionation reaction with phosphorus showing oxidation states of \(-3\) in phosphine and \(+1\) in hypophosphite. Comparing to the options provided: the question corresponds more accurately with a reaction that forms a compound with oxidation state \(+1\) than the given options, indicating a practical error in provided options.

Key Concepts

Oxidation States of Phosphorus

Understanding the oxidation states of phosphorus is key to mastering its chemistry. The oxidation state is a concept used to describe the degree of oxidation (loss of electrons) of an atom in a chemical compound. It is crucial for determining how atoms in a compound interact and bond with each other. In the context of the white phosphorus reaction with NaOH, phosphorus undergoes changes in its oxidation states.

When white phosphorus (P4) reacts, each phosphorus initially has an oxidation state of 0. During the reaction, it is both oxidized and reduced, resulting in phosphine (PH3) with phosphorus at \(-3\) and sodium hypophosphite (NaH2PO2) with phosphorus at \(+1\). Evaluating these states illustrates the electron transfer that occurs:

• White Phosphorus (P4): All phosphorus atoms begin with an oxidation state of 0.
• Phosphine (PH3): Phosphorus gains electrons, resulting in an oxidation state of \(-3\).
• Sodium Hypophosphite (NaH2PO2): Phosphorus loses electrons, attaining an oxidation state of \(+1\).

These states are calculated using basic rules for assigning oxidation numbers, such as the known states of hydrogen and oxygen and the neutrality of compounds.

Redox Reactions in Chemistry

Redox reactions, or oxidation-reduction reactions, are essential in chemistry and involve the transfer of electrons between two substances. This electron exchange is what defines an oxidation and a reduction reaction:

• Oxidation: Loss of electrons, increasing the oxidation state.
• Reduction: Gain of electrons, decreasing the oxidation state.

In the reaction of white phosphorus with NaOH, the redox nature is evident as phosphorus is both oxidized and reduced. This specific type of redox reaction is termed a disproportionation reaction where a single substance (white phosphorus in this case) undergoes both oxidation and reduction to yield two distinct products.

The change of phosphorus' state from \(0\) in P4 to \(-3\) in PH3 represents reduction, while the change from \(0\) to \(+1\) in NaH2PO2 represents oxidation.

• Reduction: \(P_4 \rightarrow PH_3\)
• Oxidation: \(P_4 \rightarrow NaH_2PO_2\)

These are characteristic of redox processes and fundamentally explain how disparate oxidation states can occur in a single reaction.

White Phosphorus Reactions

White phosphorus (P4) is a highly reactive form of the element phosphorus. Its unique bonding and tetrahedral arrangement make it an interesting participant in chemical reactions. It tends to react easily with other substances, such as water and oxygen, due to the strain on its bonds.

In reactions with bases like NaOH, white phosphorus undergoes disproportionation, a special type of chemical reaction where the element is concurrently oxidized and reduced. Here, phosphorus's reactivity is showcased:

• Reacts with oxygen: Can result in phosphorus pentoxide, an important industrial chemical.
• Reacts with water: Typically forms phosphoric acid.
• Reacts with NaOH: Yields phosphine and sodium hypophosphite, showcasing disproportionation.

These reactions display the versatility of white phosphorus and help in illustrating how reactions can yield molecules with different oxidation states from a single element's transformative processes.