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 (A) redox reaction; \(-3\) and \(-5\) (B) redox reaction; \(+3\) and \(+5\) (C) disproportionation reaction; \(-3\) and \(+5\) (D) disproportionation reaction; \(-3\) and \(+3\)

Short answer

The reaction is a disproportionation reaction; the oxidation states of phosphorus in phosphine and the other product are -3 and +5, respectively.

Step-by-step solution

Identify the type of reaction

Phosphorus reacts with aqueous NaOH producing phosphine (PH3) and another phosphorus containing compound. Since white phosphorus (P4) is being both oxidized to phosphine and another higher oxidation state phosphorus compound, this is a disproportionation reaction where the same element is simultaneously oxidizing and reducing.

Find the oxidation states of phosphorus in phosphine

In phosphine (PH3), phosphorus is bonded to hydrogen, which typically has an oxidation state of +1. Since there are three hydrogen atoms, and the overall charge of the compound is neutral, phosphorus must have an oxidation state of -3 to balance the +3 charge from hydrogen.

Determine the oxidation state of phosphorus in the other product

In the other product, phosphorus is at a higher oxidation state than in phosphine. White phosphorus starts with an oxidation state of 0. Since this is a disproportionation reaction, phosphorus must end up in both a lower and higher oxidation state. The higher oxidation state of phosphorus in compounds is typically +5, which is found in phosphate compounds.

Key concepts

Oxidation States

Understanding oxidation states is crucial for grasping many chemical reactions, especially redox processes. An oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. It denotes the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic, and it helps chemists keep track of electron transfer.
The scale of oxidation states ranges from highly negative to highly positive. For example, in a neutral molecule like phosphine ((PH_3)), the oxidation state of phosphorus is found by calculating the total number of electrons it would own if the molecule were ionic. Hydrogen generally has an oxidation state of +1, so for three hydrogens, it's a total of +3. To balance this out, phosphorus gets an oxidation state of -3 to maintain the electrically neutral state of the molecule.

Redox Reaction

Redox reactions are a family of chemical reactions that involve the transfer of electrons between two species. The term 'redox' is a shorthand for 'reduction-oxidation' reaction. In any redox reaction, one species undergoes oxidation (loss of electrons) while the other undergoes reduction (gain of electrons). These two processes always occur simultaneously in a coupled fashion.
For example, when white phosphorus reacts with sodium hydroxide, it ends up in two different phosphorus-containing compounds with varying oxidation states. This transformation from one oxidation state to another signifies that a redox reaction is taking place, with electrons being transferred from one atom to another.

Phosphine Production

Phosphine ((PH_3)) is a toxic and flammable gas that is produced industrially and in certain chemical reactions, including the reaction between white phosphorus and sodium hydroxide. In the laboratory, phosphine can be prepared by this method. The key is to provide conditions that favour the formation of the (PH_3) molecule, typically in the presence of an alkali.
During the production process, the oxidation state of phosphorus in white phosphorus ((P_4)) is 0. When it reacts with sodium hydroxide ((NaOH)) in water, a differential conversion occurs: some of the phosphorus atoms reduce to form (PH_3) with a -3 oxidation state, while others oxidize to a higher oxidation state, often as part of phosphate ions like (PO_4)^{3-}, where phosphorus has an oxidation state of +5.

White Phosphorus Chemistry

White phosphorus is an allotrope of phosphorus that is highly reactive and is typically stored under water to prevent spontaneous ignition in air. It's composed of (P_4) tetrahedrons, where each phosphorus atom donates and accepts electrons from the other phosphorus atoms, resulting in an oxidation state of 0. This allotrope is reactive because of the high strain within the (P_4) molecule and the weakness of the (P-P) bonds.
In chemistry, white phosphorus exhibits interesting reactions because of its ability to show different oxidation states under varying conditions. When it reacts with sodium hydroxide, a disproportionation reaction occurs, which is a type of redox reaction where white phosphorus is both oxidized and reduced, leading to phosphine production and other phosphorus-containing compounds with higher oxidation states, thus demonstrating the versatility of white phosphorus in chemical reactions.